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Journal ArticleDOI

Modulators of Protein-Protein Interactions

15 Apr 2014-Chemical Reviews (American Chemical Society)-Vol. 114, Iss: 9, pp 4695-4748
TL;DR: This research presents a novel and scalable approaches called “Smart Gene Regulation” that allows for real-time annotation of the FISH signal in the Eindhoven–Borff–Seiden cellular automaton.
Abstract: Lech-Gustav Milroy,† Tom N. Grossmann,‡,§ Sven Hennig,‡ Luc Brunsveld,† and Christian Ottmann*,† †Laboratory of Chemical Biology and Institute of Complex Molecular Systems, Department of Biomedical Engineering, Technische Universiteit Eindhoven, Den Dolech 2, 5612 AZ Eindhoven, The Netherlands ‡Chemical Genomics Centre of the Max Planck Society, Otto-Hahn Straße 15, 44227 Dortmund, Germany Department of Chemistry and Chemical Biology, Technical University Dortmund, Otto-Hahn-Strasse 6, 44227 Dortmund, Germany

Summary (1 min read)

■ INTRODUCTION

  • Protein−protein interactions (PPIs) are important in almost all biological processes.
  • The targeting of PPIs will be particularly valuable for diseases that cannot be addressed via "conventional" targets such as enzymes, receptors, or ion channels.
  • 44 By binding to other proteins, 14-3-3 can assist in protein folding, protein localization, and stimulation or inhibition of other PPIs.
  • 14-3-3 proteins from this parasite were shown to play a crucial role in the early stages of the infection by maintaining the host−parasite relationship.

Journal of Medicinal Chemistry

  • Residues from 14-3-3σ important for binding are shown as labeled sticks; polar contacts are depicted as black dotted lines (PDB ID: 4FL5).
  • A similar pyridoxal phosphate derivative 15C was reported by Ottmann and co-workers as a 14-3-3 proteinbinding ligand.

■ CONCLUSIONS AND FUTURE DIRECTIONS

  • The authors demonstrated that 14-3-3 proteins are highly relevant targets in drug discovery and provide a valuable tool in chemical biology.
  • Importantly, in addition to structural insights on the molecular mechanisms of the different small molecules, in a number of cases the influence on biological pathways has been studied, resulting in promising findings in cell-based model systems relevant to treating a variety of diseases (e.g., Alzheimer's disease, various cancers, asthma, and cystic fibrosis).
  • The great number of similar binding modes of 14-3-3 PPI partners makes it difficult for small molecule modulation to achieve specificity for one partner over the others.
  • By studying the "hot spots" responsible for the binding of the two partner proteins in these binary structures, the authors observe that there is a considerable variety of potentially distinct druggable pockets.
  • They act as molecular glue and thereby provide better opportunities for selectivity.

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Modulators of 14-33 ProteinProtein Interactions
Loes M. Stevers,
Eline Sijbesma,
Maurizio Botta,
Carol MacKintosh,
§
Tomas Obsil,
Isabelle Landrieu,
Ylenia Cau,
Andrew J. Wilson,
#,
Anna Karawajczyk,
Jan Eickho,
Jeremy Davis,
Michael Hann,
Gavin OMahony,
$
Richard G. Doveston,
Luc Brunsveld,
and Christian Ottmann*
,,@
Laboratory of Chemical Biology, Department of Biomedical Engineering and Institute for Complex Molecular Systems (ICMS),
Eindhoven University of Technology, P.O. Box 513, 5600 MB, Eindhoven, The Netherlands
Department of Biotechnology, Chemistry and Pharmacy, University of Siena, Via Aldo Moro 2, 53100 Siena, Italy
§
Division of Cell and Developmental Biology, School of Life Sciences, University of Dundee, Dundee DD1 4HN, United Kingdom
Department of Physical and Macromolecular Chemistry, Faculty of Science, Charles University, Prague 116 36, Czech Republic
Universite
deLille, CNRS, UMR 8576, F 59 000 Lille, France
#
School of Chemistry, University of Leeds, Woodhouse Lane, Leeds LS2 9JT, United Kingdom
Astbury Center For Structural Molecular Biology, University of Leeds, Woodhouse Lane, Leeds LS2 9JT, United Kingdom
Taros Chemicals GmbH & Co. KG, Dortmund 44227, Germany
Lead Discovery Center GmbH, Dortmund 44227, Germany
UCB Celltech, 216 Bath Road, Slough SL1 3WE, United Kingdom
GlaxoSmithKline, Gunnels Wood Road, Stevenage, Hertfordshire SG1 2NY, United Kingdom
$
Cardiovascular and Metabolic Diseases, Innovative Medicines and Early Development Biotech Unit, AstraZeneca Gothenburg,
Pepparedsleden 1, SE-431 83 Mo
lndal, Sweden
@
Department of Chemistry, University of Duisburg-Essen, Universita
tstraße 7, 45141 Essen, Germany
*
S
Supporting Information
ABSTRACT: Direct interactions between proteins are essential for the
regulation of their functions in biological pathways. Targeting the complex
network of proteinprotein interactions (PPIs) has now been widely
recognized as an attractive means to therapeutically intervene in disease
states. Even though this is a challenging endeavor and PPIs have long been
regarded as undruggable targets, the last two decades have seen an
increasing number of successful examples of PPI modulators, resulting in
growing interest in this eld. PPI modulation requires novel approaches and
the integrated eorts of multiple disciplines to be a fruitful strategy. This
perspective focuses on the hub-protein 14-3-3, which has several hundred
identied protein interaction partners, and is therefore involved in a wide
range of cellular processes and diseases. Here, we aim to provide an
integrated overview of the approaches explored for the modulation of 14-3-3
PPIs and review the examples resulting from these eorts in both inhibiting
and stabilizing specic 14-3-3 protein complexes by small molecules, peptide mimetics, and natural products.
INTRODUCTION
ProteinProtein Interactions (PPIs). Proteinprotein
interactions (PPIs) are important in almost all biological
processes. Most proteins do not function as single isolated
entities but rather are engaged in a dynamic physical network
with other proteins in the biomolecular context of a cell and its
environment, often as part of a multiprotein complex. This
makes the interactions of prot eins as important as the
biochemical activity of the protein itself. To understand the
biological role of a protein, it is of great importance to understand
and manipulate its underlying PPI network. An excellent example
of this can be found in cancer biology, where the oncogenic
kinase B-Raf can activate or inhibit the MAPK pathway by
mechanisms that involve changes in the interactions of B-Raf
with other members of the Raf kinase family.
13
The druggable genome has been initially estimated to
comprise approximately 1,500 single protein targets.
4
Although
this is still many more than the 266 human protein targets
addressed by currently approved drugs,
5
intentionally targeting
Received: April 14, 2017
Published: October 2, 2017
Perspective
pubs.acs.org/jmc
© XXXX American Chemical Society A DOI: 10.1021/acs.jmedchem.7b00574
J. Med. Chem. XXXX, XXX, XXXXXX
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J. Med. Chem.
XXXX, XXX, XXX-XXX
This is an open access article published under a Creative Commons Non-Commercial No
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PPIs signicantly enlarges this number. The targeting of PPIs will
be particularly valuable for diseases that cannot be addressed via
conventional targets such as enzymes, rece ptors, or ion
channels. By considering PPIs occurring in the human body,
this situation can undoubtedly be improved given the size of the
so-called proteinprotein interactome with estimates lying
between 130,000
6
and 650,000
7
protein complexes. Successfully
addressing PPIs will vastly expand our opportunit ies for
pharmacological intervention, especially by exploiting natural
products.
8
However, our understanding of biological mecha-
nisms, and thus also which PPIs are relevant to disease, is still
rudimentary. No further evidence of this is needed other than to
reect on the fact that the highest attrition rate during the drug-
discovery process occurs during phase II clinical trials when it
also becomes more costly.
9
This attrition all too often arises
because the desired biological eect is not observed with a given
lead candidate. The availability of a good chemical probe, in
contrast to genetic methods, uniquely allows temporary and
titratable knockdown of a protein of interest, permitting its
druggability and relevance to disease to be evaluated.
1012
Such
probes can drive fundamental biology; for instance, publications
on BRD4 (bromodomain) and hDM2 (ubiquitin ligase) have
increased dramatically since the discovery of the PPI inhibitors
bromodomain inhibitor (JQ1)
13
and Nutlin.
14
The issue of druggability is not unique to PPIs. However,
their extensive regulatory role in biological mechanisms dictates
that high-quality tool compounds modulating PPIs are urgently
required as probes of healthy/disease biology and to provide
starting points for drug discovery. Here, PPIs present a further
challenge in that the interacting surfaces are larger, atter, and
generally decient in the binding-pockets that dene conven-
tional ligandable
15,16
proteins,
9
although identication of hot-
spots
17
permits a binding site to be dened. This challenge is
suciently daunting that, until recently, PPIs were considered
too challenging to modulate using small-molecules and amenable
only to modulation using biologics.
18
However, the emergence of
PPIs as small-molecule targets has now been conclusively
demonstrated by the Nutlin series (Roche)
14
and Navitoclax
(Abbott).
22
Although traditional approaches (e.g., high-
throughput s creening, fragment-based drug d iscovery, and
computer-aided ligand design) are recognized as having
limitations in terms of the identication of hit matter,
19,20
the
development of d esign-based approaches, e.g., based on
foldamers, is encouraging.
21
A number of strategic approaches
to modulation can be envisioned comprising competitive (or
orthosteric) inhibition, allosteric inhibition, and stabilization
(Figure 1AC) with general progress in this area summarized in
numerous well-cited reviews.
16,19,20,2327
In terms of interven-
tion within a pathway, the biological eect might be complex in
that competitive inhibition of a PPI might result in stabilization
of a PPI elsewhere within the pathway. Similarly, allostery aects
not only the activation state of a given protein but the entire
pathway in which it is embedded.
28
For instance, the GTPase
activity of Ras is modulated through its PPI with SOS at a remote
site, and modulation of this interaction aects downstream PPI-
mediated kinase activity within the entire pathway.
29
In terms of ligand approaches, competitive, allosteric, and
stabilization modulatio n o f PPIs are e xtremely di erent.
Competitive inhibition is reasonably well established, and a
number of inhibitors have been identied using conventional
drug-discovery and design approaches. Prominent examples
include a Nutlin follow-up from Roche (RG7112),
30
Abbott
(ABT-199),
31
and GSK (I-BET762),
32
which all entered clinical
trials (Figure 2AC). Challenges associated with competitive
inhibition center on achieving suciently potent and selective
recognition of either protein surface for inhibition to occur and
the concomitant liability that might be introduced in terms of
inhibiting all PPIs of the target protein. The biological response is
proportional to the quality of the competitor. Allosteric
inhibition may be more challenging to achieve by design and
more likely to be identied by chance; however, allosteric
inhibitors oer increased selectivity and self-limiting activity and,
where PPIs are concerned, are much more likely to have the
Lipinski properties
33
characteristic of traditional small molecule
drugs. A number of natural products have been identied to act
through allosteric eects such as Taxol, which stabilizes tubulin
so as to retard its polymerization.
34
Drug-discovery and chemical
biology programs have also delivered allosteric modulators. For
instance, allosteric inhibitors of HIF-2 complex formation have
been identied, which act through recognition of the PAS-B
domain of the HIF-2α subunit (Figure 2D).
35
Such compounds
have been used to validate HIF-2 as a viable cancer target in renal
cell cancer.
36,37
Stabilization is less well established; however, it
features prominently among natural products Brefeldin A,
38
Forskolin,
39
and Rapamycin
40
(among others), which all act
through stabilization of a PPI (Figure 2E and F). In addition,
Tafamidis, one of the few PPI modulators to successfully reach
the clinic, stabilizes the PPI transthyretin, which normally exists
as a functional tetramer and aggregates in neurodegenerative
diseases such as transthyretin amyloidosis. Small molecules such
as Tafamidis that recognize and stabilize the tetrameric complex
have been shown to kinetically retard aggregation and thus
amyloid bril formation.
41,42
It should be noted that stabilizers of
PPIs should also exhibit self-limiting biological response and
greater selectivity because they also rely on ternary complex
formation.
Despite these advances, PPI modulation remains a largely
unsolved problem with inhibitors against only a few targets in
current clinical trials.
20
Progress is hampered by low success rates
in identifying high-quality starting points for drug discovery
19
and by a poor understanding of which PPIs may be targeted by
small molecules.
16
Improved ligand-discovery approaches and
better conceptual understanding might well arise from the study
of certain privileged protein classes. With several hundred
identied protein interaction partners in eukaryotic cells, the
family of the so-called 14-3-3 proteins is an especially interesting
case for small-molecule PPI modulation. This protein family
represents an outstanding testing ground for new conceptual
approaches to PPI modulation and the elaboration of novel
Figure 1. Schematic depicting dierent strategies for modulation of
PPIs: competitive (orthosteric) inhibition (A), allosteric inhibition (B),
and stabilization (C).
Journal of Medicinal Chemistry Perspective
DOI: 10.1021/acs.jmedchem.7b00574
J. Med. Chem. XXXX, XXX, XXXXXX
B

therapeutic approaches. PPIs of 14-3-3 proteins play key roles in
numerous disease-relevant biological pathways and oer clear
opportunities in terms of inhibition and stabilization. This
perspective will highlight the state of the art in both areas with
examples from diverse disease pathways.
14-3-3 Proteins. 14-3-3 proteins are eukaryotic adaptor
proteins involved in many cellular processes such as cell-cycle
control, signal transduction, protein tracking, and apoptosis.
44
By binding to other proteins, 14-3-3 can assist in protein folding,
protein localization, and stimulation or inhibition of other
PPIs.
45
Seven di erent mammalian 14-3-3 isoforms exist (α/β, γ,
σ, δ/ζ, η, ε, and τ), which are highly conserved throughout
species and mainly exist as dimers. Each monomer consists of
nine alpha helices forming an amphipathic groove that can bind
to (mostly phosphorylated) protein partners (Figure 3).
46
Among the several hundred 14-3-3 interaction partners
described so far, there are many disease-relevant proteins
involved in key cellular processes, like the Raf kinases,
47,48
cell-
cycle phosphatase Cdc,
49,50
transcriptional modulator YAP
51,52
and tumor suppressor p53.
53,54
This widespread involvement in
human disease makes 14-3-3 proteins a highly interesting case for
the development of technology to modulate their PPIs in a
specic and ecient manner. Because both inhibition and
stabilization of 14-3-3 PPIs have been sh own with small
molecules, the possibilities for novel pharmacological inter-
vention by addressing this protein class are substantial. In this
context, stabilization of 14-3-3 PPIs is an especially promising
approach because the problem of specicity might be solved
more easily than with inhibitors. This is due to the relatively high
variability between the respective PPI interfaces. This variability
might allow for the development of compounds that specically
bind to unique composite pockets at the PPI interfaces. In this
Figure 2. Representative examples of competitive, allosteric, and stabilizing PPI ligands (X-ray structure (above), chemical structure (below)). (A) p53/
hDM2 inhibitor RG7112 (PDB ID: 4IPF).
43
(B) BH3/Bcl-2 inhibitor ABT-199 (PDB ID: 4MAN).
31
(C) Fragment of BRD4/Histone inhibitor I-
BET762 (PDB ID: 4C66).
32
(D) HIF-2 PAS domain allosteric modulator (PDB ID: 4GHI).
35
(E) FKBP12/Rapamycin/FRAP stabilizer complex
(PDB ID: 1FAP).
40
(F) Transthyretin stabilizer (PDB ID: 2FLM).
42
Journal of Medicinal Chemistry Perspective
DOI: 10.1021/acs.jmedchem.7b00574
J. Med. Chem. XXXX, XXX, XXXXXX
C

way, not only can tool compounds be developed for the study of
the underlying biology in, e.g., cancer, neurodegeneration,
metabolic diseases, infection, and cystic brosis, but the approach
can also be exploited in terms of drug discovery. Here, control of
subcellular localization, enzymatic activity, and biological half-life
can be envisioned as modes by which 14-3-3 PPI modulators
could act, e.g., on transcription factors (YAP, c-Jun, MLF1,
FOXOs), enzymes shuttling between cytoplasm and nucleus
(Cdc25 phosphatases, HDACs), or kinases (B, C-Raf, LRRK2).
In recent years, a growing number of crystal structures of 14-3-
3 in complex with dierent binding partner motifs have been
published, for example, the cystic brosis ion channel CFTR,
55
the small heat shock protein HSPB6,
56
phosducin,
57
and the
Parkinsons disease-related kinase LRRK2.
58
As dimeric species
that dock onto pairs of specic phosphorylated serine- or
threonine-containing motifs, 14-3-3 proteins are endowed with
special signaling, mechanical, and evolutionary properties.
Although there are a few cases where a 14-3-3 dimer interacts
simultaneously with phosphorylated sites in two dierent targets,
in most documented cases a single 14-3-3 dimer binds to two
phosphorylated sites that lie in tandem in the same target protein.
This means that a 14-3-3 dimer can act as a signaling integrator
when two binding sites on a target are phosphorylated by
dierent kinases. The mechanical eect of 14-3-3 will depend on
the location of the two docking sites. For example, these paired
sites may straddle a domain or motif whose function is masked by
the 14-3-3, or 14-3-3 binding to a disordered region can force a
disorder-to-order transition that creates a new functional site in
the target.
59,60
14-3-3 binding sites lie within motifs that are phosphorylated
by basophilic protein kinases such as PKB/Akt, p90RSK, PKA,
and AMPK.
57
This means that 14-3-3 anity capture and
quantitative mass spectrometry procedures can be used to
identify targets of, for example, regulation by insulin, growth
factors, energy stress, and adrenalin that activate these respective
kinases. In this way, new 14-3-3-based mechanisms have been
identied to explain how insulin and growth factors regulate
synchronized shifts in glucose uptake, glycolysis, mTORC1
signaling, protein translation, and other regulatory events that
promote cell growth and proliferation.
6264
Their roles as
mediators of growth factor and nutrient signaling pathways are
consistent with further ndings that connect 14-3-3 proteins to a
variety of human diseases. In addition to their participation in
diverse cancers,
44
they have been associated with the develop-
ment of neurodegenerative diseases
65
and virulence of human
pathogenic organisms.
66,67
The role of 14-3-3 proteins in parasitic organisms has only
recently emerged. The rising interest in this eld is justied by
the limited panel of eective drugs currently available to treat
parasite infections, the relevant side eects associated with these
compounds, and the growing number of treatment-refractory
cases.
68
A survey of the recent literature has highlighted a number
of reports showing the role of, and in a few cases the structural
features of, 14-3-3 from parasites, which are briey reviewed here.
Plasmodium falciparum and Plasmodium knowlesi are two
species of protozoan parasites that can cause severe malaria
infection in humans.
69
In P. falciparum and P. knowlesi, the single
isoform of 14-3-3 was shown to act as a chaperone only in specic
life stages of the parasite.
68
In Plasmodium berghei, the host
skeletal protein dematin is translocated from the erythrocyte
membrane within the parasite, where it interacts with the
Plasmodium 14-3-3, thus inuencing the remodeling of the
Figure 3. 14-3-3 structure and binding of partner protein peptides exemplied by the 14-3-3ζ/C-Raf complex (PDB ID: 4FJ3).
61
Top: the physiological
14-3-3 dimer can accommodate two phosphorylated peptide motifs. In the case of C-Raf, two of these motifs (pSer233 and pSer259) are located in the
N-terminal region of this protein kinase. When synthesized as a diphospho peptide (C-RafpS233pS259) and crystallized with 14-3-3ζ dimer, a
signicant proportion of the peptide does not engage an intimate contact with 14-3-3 and is thus not visible in the X-ray crystal structure (right dimer:
green dotted line). Bottom: C-RafpS259 site accommodated in the groove of a 14-3-3ζ monomer.
Journal of Medicinal Chemistry Perspective
DOI: 10.1021/acs.jmedchem.7b00574
J. Med. Chem. XXXX, XXX, XXXXXX
D

erythrocytic cytoskeleton and modulating the host erythrocyte
invasion.
70
Eimeria tenella is a coccidian parasite that causes a serious
intestinal disease in chickens. Although human infection by E.
tenella has not been reported yet, this parasite has a signicant
economic impact with an estimated cost to the poultry industry
of around $2.4 billion per annum worldwide, thus justifying the
in depth study of its lifecycle and infection mechanisms.
71
In E.
tenella, a single isoform of 14-3-3 seems to be involved in the
regulation of the mannitol pathway. In particular, the binding of
14-3-3 to the mannitol-1-phosphate dehydrogenase (M1PDH)
was shown to inactivate the enzyme as soon as mannitol
biosynthesis is complete. From a drug discovery perspective, it is
important to note that this pathway is missing in higher
eukaryotes, thus r epresenting an attractive target for the
development of selective drugs.
68
Toxoplasma gondii is a protozoan parasite that causes a disease
known as toxoplasmosis, a generally asymptomatic infection.
Despite this, the parasite is known to cause severe congenital
infection in humans and animals. The sexual reproduction of this
parasite occurs in the intestine of denitive hosts (cats) while
asexual multiplication takes place in various hosts, including
humans.
72
14-3-3 proteins have been detected in the asexual
form of the parasite, namely the tachyzoite stage, that is virulent
in humans.
73
Moreover, it was demonstrated that, in this stage,
14-3-3 proteins from T. gondii induce hypermotility in infected
host cells.
74
Alveolar echinococcosis (AE) is a rare parasitic disorder that
occurs after ingestion of eggs of Echinococcus multilocularis.AEis
a tumorlike chronic disease, which can be fatal if left untreated.
75
In E. multilocularis, 14-3-3 proteins have been reported to be
implicated in the tumor-like growth process.
76
Furthermore, it
has been hypothesized that overexpressed 14-3-3 proteins may
be involved in the promotion and/or maintenance of the
progressive growth capacity of E. multilocularis larvae.
77
Schistosoma mansoni is one of the major intestinal parasites that
can cause schistosomiasis, the most widespread parasitic disease
after malaria. This parasite encodes four 14-3-3 isoforms that
have roles in host immunity, parasite development, and
survival.
78
Trichinella spiralis is a nematode parasite that is responsible for
the development of trichinellosis, which is an important
foodborne parasitic disease worldwide. The infection in humans
is generally acquired by eating raw or inadequately cooked meat
that contains encysted larvae of T. spiralis. 14-3-3 proteins from
this parasite were shown to play a crucial role in the early stages of
the infection by maintaining the hostparasite relationship.
79
Cryptosporidium parvum is a parasite responsible for
cryptosporidiosis, a diarrheal disease that aect humans and
animals especially in developing countries.
80
This infection is
mainly caused by the ingestion of contaminated water, and an
estimated 748,000 cryptosporidiosis cases occur annually.
81
Unfortunately, only a limited number of drugs can be used to
treat infections by C. parvum and most of them have low ecacy
and an unknown mechanism of action. The three isoforms of 14-
3-3 found in C. parvum (Cp14ε, Cp14a, and Cp14b) were
crystallized in 2011, and two of them showed some interesting
features that are unique among 14-3-3 proteins.
80
In particular, in
the isoform Cp14a, the substrate pocket is much more open
compared to the classical folding of 14-3-3, leading to the
hypothesis that this isoform can accommodate large substrates.
The Cp14b isoform was able to bind a phosphorylated copy of
the last six amino acid residues of its own C-terminus. This
binding is much stronger when the C-terminus is truncated, thus
suggesting a competition between C-terminus and its
phosphorylated mimic.
80
Even if other studies are necessary to
understand the role of 14-3-3 in the C. parvum life cycle, these
unique features described above can be exploited to develop
novel strategies for cryptosporidiosis treatment.
Giardia duodenalis is a protozoan parasite that causes giardiasis
by colonizing the upper portion of the small intestine in
mammals. Giardiasis is the most common gastr ointestinal
diarrheal illness worldwide, and more than 200 million
symptomatic human cases are reported annually.
82,83
In this
parasite, the single 14-3-3 isoform (g14-3-3) is essential for the
development of cysts (the infective stage).
84
Three crystallographic structures of G. duodenalis are available,
which makes this protein amenable to study through structure-
based computational methods. The crystal structure of g14-3-3 in
the apo form revealed an unusual open conformation,
85
whereas computational studies (supported by crystallographic
evidence) proved that the post-translational modication
(phosphorylation) on Thr214 of g14-3-3 induces a conforma-
tional rearrangement that leads to the closed and stable g14-3-3
conformation.
84
This form corresponds to the peptide-bound
g14-3-3 structure.
In summary, all these ndings demonstrate that 14-3-3
proteins have substantial involvement in parasites life cycles.
Even if the molecular basis for the role of 14-3-3 in pathogenicity
is not well understood, we can speculate that this protein family
could represent an alternative and promising axis to treat parasite
infections. Despite rising interest in the role of 14-3-3 in
parasites, signicant advancement in basic research is required.
Specically, the development of a 14-3-3 modulator could be
essential for unravelling the contribution of 14-3-3 proteins to
parasite growth and survival in the host.
In general, the ubiquity of 14-3-3 protein involvement in
numerous human diseases has sparked interest in their use as
novel targets for drug discovery.
44,49,65,86
The fact that 14-3-3
proteins serve purely as adapter proteins means that active
compounds against 14-3-3 alone will impact several binding
partners and thus likely give rise to unwanted pharmacology.
However, if the drugs target the complex formation between 14-
3-3 and a protein partner, either by inhibition or stabilization,
then intrinsic specicity should be possible.
24
Structural Biology of 14-3-3 PPIs. Most PDB entries of 14-
3-3 crystal structures represent binary complexes of 14-3-3 with a
peptide mimic of the phosphorylated binding site of the PPI
partner protein. Only in a limited number of cases has
crystallization of 14-3-3 with a larger part of the partner protein
been possible. One reason for the diculty in obtaining full-
length structures of these complexes is the fact that the partner
proteins themselves are often multidomain proteins and thus
challenging to crystallize. A second reason is that the 14-3-3
binding sequences are prevalently localized in disordered regions
of their target proteins and only undergo a disorder-to-order
transition when binding to 14-3-3. In this transition, it is
common for only the directly neighboring parts of the
phosphorylated anchor residues to be involved. Thus, large
parts of the partner protein regions remain disordered, which is a
disadvantage for crystal growth. A commonly adopted alternative
strategy therefore centers on using synthetic peptides comprising
around 1040 amino acid residues to mimic the partner protein
binding motif. It is of course vital that the activity of any stabilizer
or inhibitor found using the simplied 14-3-3/partner-protein-
peptide system is also shown in the context of more
Journal of Medicinal Chemistry Perspective
DOI: 10.1021/acs.jmedchem.7b00574
J. Med. Chem. XXXX, XXX, XXXXXX
E

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Journal Article
TL;DR: Why interactome networks are important to consider in biology, how they can be mapped and integrated with each other, what global properties are starting to emerge from interactome network models, and how these properties may relate to human disease are detailed.
Abstract: Complex biological systems and cellular networks may underlie most genotype to phenotype relationships. Here, we review basic concepts in network biology, discussing different types of interactome networks and the insights that can come from analyzing them. We elaborate on why interactome networks are important to consider in biology, how they can be mapped and integrated with each other, what global properties are starting to emerge from interactome network models, and how these properties may relate to human disease.

1,323 citations

Journal ArticleDOI
TL;DR: The past 20 years have seen many advances in understanding of protein-protein interactions (PPIs) and how to target them with small-molecule therapeutics; since then, potent inhibitors have been developed for diverse protein complexes, and compounds are now in clinical trials for six targets.

834 citations


Cites background from "Modulators of Protein-Protein Inter..."

  • ...Building on the function of natural products, there will also be greater emphasis on synthetic stabilizers of PPIs (Milroy et al., 2014)....

    [...]

Journal ArticleDOI
TL;DR: A new classification of peptidomimetics (classes A–D) is introduced that enables a clear assignment of available approaches for the structure-based design of PPI inhibitors through stabilizing or mimicking turns, β-sheets, and helices.
Abstract: Protein–protein interactions (PPIs) are involved at all levels of cellular organization, thus making the development of PPI inhibitors extremely valuable The identification of selective inhibitors is challenging because of the shallow and extended nature of PPI interfaces Inhibitors can be obtained by mimicking peptide binding epitopes in their bioactive conformation For this purpose, several strategies have been evolved to enable a projection of side chain functionalities in analogy to peptide secondary structures, thereby yielding molecules that are generally referred to as peptidomimetics Herein, we introduce a new classification of peptidomimetics (classes A–D) that enables a clear assignment of available approaches Based on this classification, the Review summarizes strategies that have been applied for the structure-based design of PPI inhibitors through stabilizing or mimicking turns, β-sheets, and helices

491 citations

Journal ArticleDOI
TL;DR: A previously understudied benefit of small molecule proteolysis-targeting chimeras (PROTACs) that recruit E3 ubiquitin ligases to target proteins for their ubiquitination and subsequent proteasome-mediated degradation is reported.

487 citations


Cites background from "Modulators of Protein-Protein Inter..."

  • ...In this situation, high-throughput techniques to screen a larger volume of compounds for ternary complex formation, rather than degradation, could be employed (Milroy et al., 2014)....

    [...]

References
More filters
Journal ArticleDOI
TL;DR: In this article, a quantenmechanische behandlung des Ubergangs von Elektronenanregungsenergie zwischen gleichartigen Molekulen in Losung gegeben.
Abstract: In Weiterentwicklung fruherer Theorien von J. und F. Perrin und klassischphysikalischer Uberlegungen des Verfassers wird eine quantenmechanische Behandlung des Ubergangs von Elektronenanregungsenergie zwischen gleichartigen Molekulen in Losung gegeben. Der kritische Molekulabstand, unterhalb dessen der ubergang wahrend der Anregungsdauer stattfindet, last sich aus den Absorptions- und Fluoreszenzspektren und der Anregungsdauer der Molekule berechnen. Fur Fluorescein und Chlorophyll a ergeben sich Werte von 50 bzw. 80 AE, entsprechend den mittleren Molekulabstanden in Losungen von 3,2 · 10−3 bzw. 7,7 · 10−4 Molen/Liter. Fur die Bereiche oberhalb und unterhalb der kritischen Konzentration werden Formeln zur Berechnung der Energieabwanderung vom Primarmolekul angegeben, die mit den vorliegenden Messungen der Konzentrationsdepolarisation der Fluoreszenz gut ubereinstimmen. Die Anwendung auf analoge Energiewanderungsprobleme in Molekulkristallen und im Assimilationsapparat der Pflanze wird diskutiert.

7,177 citations

Journal ArticleDOI
15 Dec 1995-Cell
TL;DR: This research presents a new probabilistic procedure called ‘spot-spot analysis’ to characterize the response of the immune system to the presence of E.coli.

6,818 citations

Journal ArticleDOI
TL;DR: The relative importance of the common main-chain and side-chain interactions in determining the propensities of proteins to aggregate is discussed and some of the evidence that the oligomeric fibril precursors are the primary origins of pathological behavior is described.
Abstract: Peptides or proteins convert under some conditions from their soluble forms into highly ordered fibrillar aggregates. Such transitions can give rise to pathological conditions ranging from neurodegenerative disorders to systemic amyloidoses. In this review, we identify the diseases known to be associated with formation of fibrillar aggregates and the specific peptides and proteins involved in each case. We describe, in addition, that living organisms can take advantage of the inherent ability of proteins to form such structures to generate novel and diverse biological functions. We review recent advances toward the elucidation of the structures of amyloid fibrils and the mechanisms of their formation at a molecular level. Finally, we discuss the relative importance of the common main-chain and side-chain interactions in determining the propensities of proteins to aggregate and describe some of the evidence that the oligomeric fibril precursors are the primary origins of pathological behavior.

5,897 citations

Journal ArticleDOI
06 Feb 2004-Science
TL;DR: In this article, the authors identify potent and selective small-molecule antagonists of MDM2 and confirm their mode of action through the crystal structures of complexes, leading to cell cycle arrest, apoptosis, and growth inhibition of human tumor xenografts.
Abstract: MDM2 binds the p53 tumor suppressor protein with high affinity and negatively modulates its transcriptional activity and stability. Overexpression of MDM2, found in many human tumors, effectively impairs p53 function. Inhibition of MDM2-p53 interaction can stabilize p53 and may offer a novel strategy for cancer therapy. Here, we identify potent and selective small-molecule antagonists of MDM2 and confirm their mode of action through the crystal structures of complexes. These compounds bind MDM2 in the p53-binding pocket and activate the p53 pathway in cancer cells, leading to cell cycle arrest, apoptosis, and growth inhibition of human tumor xenografts in nude mice.

4,397 citations

Journal ArticleDOI
TL;DR: This review is an updated and expanded version of the three prior reviews and adds a new designation, "natural product botanical" or "NB", to cover those botanical "defined mixtures" that have now been recognized as drug entities by the FDA and similar organizations.
Abstract: This review is an updated and expanded version of the three prior reviews that were published in this journal in 1997, 2003, and 2007. In the case of all approved therapeutic agents, the time frame has been extended to cover the 30 years from January 1, 1981, to December 31, 2010, for all diseases worldwide, and from 1950 (earliest so far identified) to December 2010 for all approved antitumor drugs worldwide. We have continued to utilize our secondary subdivision of a “natural product mimic” or “NM” to join the original primary divisions and have added a new designation, “natural product botanical” or “NB”, to cover those botanical “defined mixtures” that have now been recognized as drug entities by the FDA and similar organizations. From the data presented, the utility of natural products as sources of novel structures, but not necessarily the final drug entity, is still alive and well. Thus, in the area of cancer, over the time frame from around the 1940s to date, of the 175 small molecules, 131, or 74...

4,271 citations

Frequently Asked Questions (4)
Q1. What have the authors contributed in "Modulators of 14-3‐3 protein−protein interactions" ?

Here, the authors aim to provide an integrated overview of the approaches explored for the modulation of 14-3-3 PPIs and review the examples resulting from these efforts in both inhibiting and stabilizing specific 14-3-3 protein complexes by small molecules, peptide mimetics, and natural products. 

Research topics he likes to dive into together with group members and colleagues include nuclear receptors, protein−protein interactions, synthetic signaling systems, and supramolecular protein assemblies. 

He obtained his Ph.D. in Organic Chemistry from Southampton University under the guidance of Professor Richard Whitby before joining Celltech as a medicinal chemist in 1993. 

Carol MacKintosh is Professor of Molecular Signaling in the University of Dundee, where she is also Head of Postgraduate Studies in the School of Life Sciences.