Author
Leah S. Witus
Other affiliations: Northwestern University, Lawrence Berkeley National Laboratory, University of California, Berkeley ...read more
Bio: Leah S. Witus is an academic researcher from Macalester College. The author has contributed to research in topics: Bioconjugation & Transamination. The author has an hindex of 13, co-authored 17 publications receiving 607 citations. Previous affiliations of Leah S. Witus include Northwestern University & Lawrence Berkeley National Laboratory.
Topics: Bioconjugation, Transamination, Rotaxane, Carbon nanotube, Pairing
Papers
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TL;DR: This Account discusses protein-based carriers that can deliver drugs and imaging agents to diseased tissues, and a series of chemical strategies that can install dyes, radiolabels, MRI contrast agents, and anticancer drugs on the inside surface of these capsids.
Abstract: The uniquely diverse structures and functions of proteins offer many exciting opportunities for creating new materials with advanced properties. Exploiting these capabilities requires a set of versatile chemical reactions that can attach nonnatural groups to specific locations on protein surfaces. Over the years, we and others have developed a series of new techniques for protein bioconjugation, with a particular emphasis on achieving high site selectivity and yield. Using these reactions, we have been able to prepare a number of new materials with functions that depend on both the natural and the synthetic components. In this Account, we discuss our progress in protein bioconjugation over the past decade, focusing on three distinct projects.We first consider our work to harness sunlight artificially by mimicking features of the photosynthetic apparatus, with its beautifully integrated system of chromophores, electron transfer groups, and catalytic centers. Central to these photosystems are light-harvesti...
137 citations
TL;DR: N-Methylpyridinium-4-carboxaldehyde benzenesulfonate salt (Rapoport's salt, RS) was identified as a highly effective transamination reagent when paired with glutamate-terminal peptides and proteins and demonstrated that RS can be used to modify the heavy chains of the wild-type antibody or to modify both the heavy and the light chains after N- terminal sequence mutation to add additional glutamate residues.
Abstract: The controlled attachment of synthetic groups to proteins is important for a number of fields, including therapeutics, where antibody–drug conjugates are an emerging area of biologic medicines. We have previously reported a site-specific protein modification method using a transamination reaction that chemoselectively oxidizes the N-terminal amine of a polypeptide chain to a ketone or an aldehyde group. The newly introduced carbonyl can be used for conjugation to a synthetic group in one location through the formation of an oxime or a hydrazone linkage. To expand the scope of this reaction, we have used a combinatorial peptide library screening platform as a method to explore new transamination reagents while simultaneously identifying their optimal N-terminal sequences. N-Methylpyridinium-4-carboxaldehyde benzenesulfonate salt (Rapoport’s salt, RS) was identified as a highly effective transamination reagent when paired with glutamate-terminal peptides and proteins. This finding establishes RS as a transa...
98 citations
TL;DR: A highly reactive alanine-lysine motif emerged, which was confirmed to promote the modification of peptide substrates with PLP and appears to provide a significant improvement in the reliability with which the PLP-mediated bioconjugation reaction can be used.
Abstract: Chemical reactions that facilitate the attachment of synthetic groups to proteins are useful tools for the field of chemical biology and enable the incorporation of proteins into new materials. We have previously reported a pyridoxal 5'-phosphate (PLP)-mediated reaction that site-specifically oxidizes the N-terminal amine of a protein to afford a ketone. This unique functional group can then be used to attach a reagent of choice through oxime formation. Since its initial report, we have found that the N-terminal sequence of the protein can significantly influence the overall success of this strategy. To obtain short sequences that lead to optimal conversion levels, an efficient method for the evaluation of all possible N-terminal amino acid combinations was needed. This was achieved by developing a generalizable combinatorial peptide library screening platform suitable for the identification of sequences that display high levels of reactivity toward a desired bioconjugation reaction. In the context of N-terminal transamination, a highly reactive alanine-lysine motif emerged, which was confirmed to promote the modification of peptide substrates with PLP. This sequence was also tested on two protein substrates, leading to substantial increases in reactivity relative to their wild-type termini. This readily encodable tripeptide thus appears to provide a significant improvement in the reliability with which the PLP-mediated bioconjugation reaction can be used. This study also provides an important first example of how synthetic peptide libraries can accelerate the discovery and optimization of protein bioconjugation strategies.
80 citations
TL;DR: A series of peptides that non-covalently solubilize carbon nanotubes in water using a design motif that combines a combinatorial library sequence to bind to nanot tubes with a rationally designed section to create environmentally tuned solubility characteristics are presented.
Abstract: Methods which solubilize single-walled carbon nanotubes (SWNTs) in water as individuals, not bundles, while retaining their unique electronic, photonic and mechanical properties are highly desirable. Furthermore, functionalization with a diverse array of selectable chemical moieties would allow the range of useful applications to be significantly extended and may permit the designed assembly of SWNT networks. This paper presents a series of peptides that non-covalently solubilize carbon nanotubes in water using a design motif that combines a combinatorial library sequence to bind to nanotubes with a rationally designed section to create environmentally tuned solubility characteristics. The ability of the peptides to individually disperse carbon nanotubes without altering their electronic structure is shown by vis-NIR absorbance, fluorescence, and regular and vitreous ice cryo-TEM. Identification of the species composition of each sample by NIR fluorescence reveals that the peptides exhibit some diameter selectivity. Additionally, one of the rationally designed modifications addresses the poor stability of non-covalently solubilized SWNT suspensions by including cysteine residues for covalent crosslinking between adjacent peptides.
75 citations
TL;DR: Photometric and spectral measurements revealed that emission in the common biocompatible coating agents Pluronic F127, ss-DNA, and BSA is approximately an order of magnitude weaker than in the bioincompatible ionic surfactant SDBS.
Abstract: A series of self-assembling multidomain peptides have been designed, synthesized, and tested for their ability to individually suspend single-walled carbon nanotubes (SWCNTs) in water while preserving strong near-IR nanotube luminescence. Photometric and spectral measurements on individual SWCNTs revealed that emission in the common biocompatible coating agents Pluronic F127, ss-DNA, and BSA is approximately an order of magnitude weaker than in the bioincompatible ionic surfactant SDBS. By contrast, one of the engineered peptides gave SWCNT emission ∼40% as intense as in SDBS. A strong inverse correlation was also found between the spectral line widths of coated SWCNTs and the efficiency of their emission. Peptides with rationally designed self-assembly properties appear to be promising coatings that may enable SWCNT optical sensing applications in biological environments.
67 citations
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TL;DR: It is shown here how CNTs formed following Halogenation, followed by Direct Formation on Defect Sites, and the subsequent Encapsulation of Inorganic Substances led to the formation of CNT’s with Metal Nanoparticles.
Abstract: 2.3. Ionic Liquids (ILs) 5374 2.4. Complexation Reactions on Oxidized CNTs 5375 2.5. Halogenation 5376 2.6. Cycloaddition Reactions 5377 2.7. Radical Additions 5379 2.8. Nucleophilic Additions 5381 2.9. Electrophilic Additions 5381 2.10. Electrochemical Modifications 5381 2.11. Plasma-Activation 5381 2.12. Mechanochemical Functionalizations 5382 3. Noncovalent Interactions 5382 3.1. Polynuclear Aromatic Compounds 5382 3.2. Interactions with Other Substances 5384 3.3. Interactions with Biomolecules 5385 4. Endohedral Filling 5386 4.1. Encapsulation of Fullerenes 5386 4.2. Encapsulation of Organic Substances 5387 4.3. Encapsulation of Inorganic Substances 5387 5. Decoration of CNTs with Metal Nanoparticles 5388 5.1. Covalent Linkage 5388 5.2. Direct Formation on Defect Sites 5388 5.3. Electroless Deposition 5388 5.4. Electrodeposition 5389 5.5. Chemical Decoration 5390 5.6. Deposition of Nanoparticles onto CNTs 5391 5.7. π-π Stacking and Electrostatic Interactions 5391 6. Concluding Remarks 5392 7. Acknowledgments 5392 8. References 5392
1,127 citations
TL;DR: In this paper, the authors present an overview of the relationship between organic chemistry and natural products, focusing on the Stereochemistry and the Chemistry of Natural Products (SCHP).
Abstract: Organic Chemistry By Dr. I. L. Finar. Vol. 2: Stereochemistry and the Chemistry of Natural Products. Pp. xi + 733. (London and New York: Longmans, Green and Co., Ltd., 1956.) 40s. net.
1,037 citations
830 citations
TL;DR: This work is funded by the European Commission (Marie Curie CIG) and Ministerio de Ciencia e Innovacion, Spain (Juan de la Cierva Fellowship).
Abstract: O.B. thanks the European Commission (Marie Curie CIG) and Ministerio de Ciencia e Innovacion, Spain (Juan de la Cierva Fellowship). G.J.L.B. thanks his generous sources of funding: Royal Society, FCT Portugal (FCT Investigator), European Commission (Marie Curie CIG), and the EPSRC. G.J.L.B. is a Royal Society University Research Fellow. The authors thank Paula Boutureira Regla and Francisco Pinteus da Cruz Lopes Bernardes for inspiration.
781 citations
TL;DR: There are now various methods for achieving selective modification of both natural and unnatural amino acids--each with merits and limitations--providing a 'toolkit' that until 20 years ago was largely limited to reactions at nucleophilic cysteine and lysine residues.
Abstract: Chemical modification of proteins is an important tool for probing natural systems, creating therapeutic conjugates and generating novel protein constructs. Site-selective reactions require exquisite control over both chemo- and regioselectivity, under ambient, aqueous conditions. There are now various methods for achieving selective modification of both natural and unnatural amino acids--each with merits and limitations--providing a 'toolkit' that until 20 years ago was largely limited to reactions at nucleophilic cysteine and lysine residues. If applied in a biologically benign manner, this chemistry could form the basis of true Synthetic Biology.
745 citations