Lynn E. Bretscher

Bio: Lynn E. Bretscher is an academic researcher from University of Wisconsin-Madison. The author has contributed to research in topics: Triple helix & Peptide bond. The author has an hindex of 6, co-authored 8 publications receiving 1482 citations.

Code for collagen's stability deciphered

Abstract: The most abundant protein in animals is collagen In connective tissue, this protein is present as chains wound in tight triple helices which are organized into fibrils of great tensile strength and thermal stability1,2 We propose a new explanation for this stability

Conformational Stability of Collagen Relies on a Stereoelectronic Effect

Abstract: A polypeptide chain can adopt many conformations. Yet, the sequence of its amino acid residues directs folding to a particular native state.1 The loss of conformational entropy associated with folding destabilizes the native state. This destabilization is overcome by the hydrophobic effect, hydrogen bonds, other noncovalent interactions, and disulfide bonds.2 We have identified another force that can contribute to the conformational stability of a protein. The structure and reactivity of an organic molecule can rely on the stereochemistry of its electron pairs, bonded or nonbonded.3 Such stereoelectronic effects, which arise from the mixing of an electron pair with the antibonding σ* of an adjacent polar bond (C-X, where X ) N or O), endow nucleic acids and carbohydrates with conformational stability.4 For example, the multiple gauche effects (X-C-C-X) arising from a 2′ oxygen distinguish RNA‚RNA and RNA‚DNA duplexes from DNA‚DNA duplexes.5 The anomeric effect (X-C-X) enhances the stability of the R anomer of glycosides.6 Here, we demonstrate for the first time that a stereoelectronic effect is critical for the conformational stability of a protein. Collagen is the most abundant protein in animals.7 For example, collagen comprises one-third of the protein in humans and threefourths of the weight of human skin. The polypeptide chains of collagen are composed of approximately 300 repeats of the sequence XaaYaaGly, where Xaa is often an L-proline (Pro) residue and Yaa is often a 4(R)-hydroxy-L-proline (Hyp) residue. These chains are wound in tight triple helices, which are organized into fibrils of great tensile strength. Pro and Hyp comprise nearly one-fourth of the residues in common types of collagen.8 This prevalence of tertiary amides has dichotomous consequences for conformational stability. Pro and Hyp residues are constrained by their pyrrolidine rings, and this rigidity stabilizes triple-helical collagen.9 Yet, the trans and cis conformations of the peptide bonds to Pro and Hyp residues are of nearly equal free energy, which destabilizes collagen because all peptide bonds in triple-helical collagen are in the trans conformation (Figure 1).10 The 4(R)-hydroxyl group of the prevalent Hyp residues increases dramatically the conformational stability of collagen.11 We had shown previously that this increase arises from inductive effects.12 Can a stereoelectronic effect influence Ktrans/cis? To answer this question, we synthesized residue mimics of the form AcYaaOMe, where Yaa is Pro, Hyp, 4(S)-hydroxy-L-proline (hyp), 4(R)-fluoroL-proline (Flp), or 4(S)-fluoro-L-proline (flp).13 We chose Flp and flp because fluorine is small and electronegative and forms only weak hydrogen bonds when bound to carbon.14,15 We chose a methyl ester rather than an amide to prevent γ-turn formation, as had been observed in AcProNHMe.16 We find that the electronegativity and stereochemistry of the 4-substituent in the Yaa mimics has a significant effect on Ktrans/cis (Table 1). Compared to a flp residue, a Pro residue is twice as likely and a Flp residue is 3 times as likely to have a trans peptide bond. Does the value of Ktrans/cis have an impact on collagen stability? To answer this question, we synthesized (ProYaaGly)7 strands containing Flp or flp residues in the Yaa position.19 These strands are diastereomeric, differing only in the stereochemistry at Cγ of the Yaa residues. We found that a (ProFlpGly)7 triple helix has a Tm of 45 °C.20 In contrast, a (ProflpGly)7 triple helix has a Tm of <2 °C (Table 1). A (ProHypGly)7 triple helix has an intermediate Tm of 36 °C. Thus, both the electronegativity and

Collagen stability: insights from NMR spectroscopic and hybrid density functional computational investigations of the effect of electronegative substituents on prolyl ring conformations

Abstract: Collagen-like peptides of the type (Pro-Pro-Gly)10 fold into stable triple helices. An electron-withdrawing substituent at the Hγ3 ring position of the second proline residue stabilizes these triple helices. The aim of this study was to reveal the structural and energetic origins of this effect. The approach was to obtain experimental NMR data on model systems and to use these results to validate computational chemical analyses of these systems. The most striking effects of an electron-withdrawing substituent are on the ring pucker of the substituted proline (Proi) and on the trans/cis ratio of the Xaai-1−Proi peptide bond. NMR experiments demonstrated that N-acetylproline methyl ester (AcProOMe) exists in both the Cγ-endo and Cγ-exo conformations (with the endo conformation slightly preferred), N-acetyl-4(R)-fluoroproline methyl ester (Ac-4R-FlpOMe) exists almost exclusively in the Cγ-exo conformation, and N-acetyl-4(S)-fluoroproline methyl ester (Ac-4S-FlpOMe) exists almost exclusively in the Cγ-endo co...

Effect of 3-hydroxyproline residues on collagen stability.

Abstract: Collagen is an integral part of many types of connective tissue in animals, especially skin, bones, cartilage, and basement membranes. A fibrous protein, collagen has a triple-helical structure, which is comprised of strands with a repeating Xaa-Yaa-Gly sequence. l-Proline (Pro) and 4(R)-hydroxy-l-proline (4-Hyp) residues occur most often in the Xaa and Yaa positions. The 4-Hyp residue is known to increase markedly the conformational stability of a collagen triple helix. In natural collagen, a 3(S)-hydroxy-l-proline (3-Hyp) residue occurs in the sequence: 3-Hyp-4-Hyp-Gly. Its effect on collagen stability is unknown. Here, two host−guest peptides containing 3-Hyp are synthesized: (Pro-4-Hyp-Gly)3-3-Hyp-4-Hyp-Gly-(Pro-4-Hyp-Gly)3 (peptide 1) and (Pro-4-Hyp-Gly)3-Pro-3-Hyp-Gly-(Pro-4-Hyp-Gly)3 (peptide 2). The 3-Hyp residues in these two peptides diminish triple-helical stability in comparison to Pro. This destabilization is small when 3-Hyp is in the natural Xaa position (peptide 1). There, the inductive ...

Collagen Structure and Stability

Abstract: Collagen is the most abundant protein in animals. This fibrous, structural protein comprises a right-handed bundle of three parallel, left-handed polyproline II-type helices. Much progress has been made in elucidating the structure of collagen triple helices and the physicochemical basis for their stability. New evidence demonstrates that stereoelectronic effects and preorganization play a key role in that stability. The fibrillar structure of type I collagen—the prototypical collagen fibril—has been revealed in detail. Artificial collagen fibrils that display some properties of natural collagen fibrils are now accessible using chemical synthesis and self-assembly. A rapidly emerging understanding of the mechanical and structural properties of native collagen fibrils will guide further development of artificial collagenous materials for biomedicine and nanotechnology.

Understanding organofluorine chemistry. An introduction to the C–F bond

Abstract: Fluorine is the most electronegative element in the periodic table. When bound to carbon it forms the strongest bonds in organic chemistry and this makes fluorine substitution attractive for the development of pharmaceuticals and a wide range of speciality materials. Although highly polarised, the C–F bond gains stability from the resultant electrostatic attraction between the polarised Cδ+ and Fδ– atoms. This polarity suppresses lone pair donation from fluorine and in general fluorine is a weak coordinator. However, the C–F bond has interesting properties which can be understood either in terms of electrostatic/dipole interactions or by considering stereoelectronic interactions with neighbouring bonds or lone pairs. In this tutorial review these fundamental aspects of the C–F bond are explored to rationalise the geometry, conformation and reactivity of individual organofluorine compounds.

Applications of Fluorine in Medicinal Chemistry

Abstract: The role of fluorine in drug design and development is expanding rapidly as we learn more about the unique properties associated with this unusual element and how to deploy it with greater sophistication. The judicious introduction of fluorine into a molecule can productively influence conformation, pKa, intrinsic potency, membrane permeability, metabolic pathways, and pharmacokinetic properties. In addition, 18F has been established as a useful positron emitting isotope for use with in vivo imaging technology that potentially has extensive application in drug discovery and development, often limited only by convenient synthetic accessibility to labeled compounds. The wide ranging applications of fluorine in drug design are providing a strong stimulus for the development of new synthetic methodologies that allow more facile access to a wide range of fluorinated compounds. In this review, we provide an update on the effects of the strategic incorporation of fluorine in drug molecules and applications in po...

Differential Roles of M1 and M2 Microglia in Neurodegenerative Diseases

Abstract: One of the most striking hallmarks shared by various neurodegenerative diseases, including Parkinson's disease, Alzheimer's disease (AD), and amyotrophic lateral sclerosis, is microglia-mediated neuroinflammation. Increasing evidence indicates that microglial activation in the central nervous system is heterogeneous, which can be categorized into two opposite types: M1 phenotype and M2 phenotype. Depending on the phenotypes activated, microglia can produce either cytotoxic or neuroprotective effects. In this review, we focus on the potential role of M1 and M2 microglia and the dynamic changes of M1/M2 phenotypes that are critically associated with the neurodegenerative diseases. Generally, M1 microglia predominate at the injury site at the end stage of disease, when the immunoresolution and repair process of M2 microglia are dampened. This phenotype transformation is very complicated in AD due to the phagocytosis of regionally distributed β-amyloid (Aβ) plaque and tangles that are released into the extracellular space. The endogenous stimuli including aggregated α-synuclein, mutated superoxide dismutase, Aβ, and tau oligomers exist in the milieu that may persistently activate M1 pro-inflammatory responses and finally lead to irreversible neuron loss. The changes of microglial phenotypes depend on the disease stages and severity; mastering the stage-specific switching of M1/M2 phenotypes within appropriate time windows may provide better therapeutic benefit.

Fluorine in medicinal chemistry and chemical biology

Abstract: Introduction Chapter 1 "Unique Properties of Fluorine and Their Relevance to Medicinal Chemistry and Chemical Biology" by Takashi Yamazaki, Takeo Taguchi and Iwao Ojima Medicinal Chemistry Chapter 2 "Fluorinated Prostanoids: Development of Tafluprost, a New Anti-glaucoma Agent" by Yasushi Matsumura Chapter 3 "Fluorinated conformationally restricted glutamate analogs for CNS drug discovery and development" by Atsuro Nakazato Chapter 4 "Fluorinated Inhibitors of Matrix Metalloproteinases" by Roberta Sinisi, Monika Jagodzinska, Gabriele Candiani, Florent Huguenot, Monica Sani, Alessandro Volonterio, Raffaella Maffezzoni and Matteo Zanda Chapter 5 "Fluoro-Taxoid Anticancer Agents" by Antonella Pepe, Larisa Kuznetsova, Liang Sun and Iwao Ojima Chapter 6 "Antimalarial Fluoroartemisinins: Increased Metabolic and Chemical Stability"by Jean-Pierre Begue, Daniele Bonnet-Delpon Chapter 7 "Synthesis and Biological Activity of Fluorinated Nucleosides" by Tokumi Maruyama, Masahiro Ikejiri, Kunisuke Izawa and Tomoyuki Onishi Synthetic methods for medicinal chemistry and chemical biology Chapter 8 "Synthesis of gem -Difluoromethylenated Nucleosides via gem -Difluoromethylene-Containing Building Blocks" by Wei-Dong Meng and Feng-Ling Qing Chapter 9 "Recent Advances in the Syntheses of Fluorinated Amino Acids" by Kenji Uneyama Chapter 10 "Fluorinated Moieties for Replacement of Amide and Peptide Bonds" by Takeo Taguchi and Hikaru Yanai Chapter 11 "Perfluorinated Heteroaromatic Systems as Scaffolds for Drug Discovery" by David Armstrong, Matthew W. Cartwright, Emma L. Parks, Graham Pattison, Graham Sandford, Rachel Slater, John A. Christopher, David D. Miller, Paul W. Smith and Antonio Vong Chapter 12 " gem -Difluorocyclopropanes as key building blocks for novel biologically active molecules" by Toshiyuki Itoh Chapter 13 "Fluorous Mixture Synthesis (FMS) of Drug-Like Molecules and Enantiomers, Stereoisomers, and Analogs of Natural Products" by Wei Zhang Chapter 14 "Fluorine-18 Radiopharmaceuticals" by Michael R. Kilbourn and Xia Shao Applications of fluorinated amino acids and peptides to chemical biology and pharmacology Chapter 15 "Application of Artificial Model Systems to Study the Interactions of Fluorinated Amino Acids within the Native Environment of Coiled Coil Proteins" by Mario Salwiczek, Toni Vagt and Beate Koksch Chapter 16 "Fluorinated Amino Acids and Biomolecules in Protein Design and Chemical Biology" by He Meng, Ginevra A. Clark , and Krishna Kumar Chapter 17 "Effects of Fluorination on the Bioorganic Properties of Methionine" by John F. Honek Chapter 18 "Structure analysis of membrane-active peptides using 19 F-labeled amino acids and solid state NMR" by Parvesh Wadhwani and Erik Strandberg Chapter 19 "Metabolism of Fluorine-containing Drugs using in vivo Magnetic Resonance Spectroscopy" by Erika Schneider Appendix "FDA-Approved Active Pharmaceutical Ingredients Containing Fluorine" by Elizabeth Pollina-Cormier, Manisha Das, and Iwao Ojima