Peptide Bond Formation in Water Mediated by Carbon Disulfide.

Demonstrating plausible nonenzymatic polymerization mechanisms for prebiotic monomers represents a fundamental goal in prebiotic chemistry. While a great deal is now known about the potentially prebiotic synthesis of amino acids, our understanding of abiogenic polymerization processes to form polypeptides is less well developed. Here, we show that carbon disulfide (CS2), a component of volcanic emission and sulfide mineral weathering, and a widely used synthetic reagent and solvent, promotes peptide bond formation in modest yields (up to ∼20%) from α-amino acids under mild aqueous conditions. Exposure of a variety of α-amino acids to CS2 initially yields aminoacyl dithiocarbamates, which in turn generate reactive 2-thiono-5-oxazolidone intermediates, the thio analogues of N-carboxyanhydrides. Along with peptides, thiourea and thiohydantoin species are produced. Amino acid stereochemistry was preserved in the formation of peptides. Our findings reveal that CS2 could contribute to peptide bond formation, and possibly other condensation reactions, in abiogenic settings.

Chemically programmed antibodies targeting multiple alpha(v) integrins and their effects on tumor-related functions in vitro.

Integrins αvß3 and αvß6 are highly expressed on tumor cells and/or by the tumor vasculature of many human cancers, and represent promising targets for anticancer therapy. Novel chemically programmed antibodies (cpAbs) targeting these integrins were prepared using the catalytic aldolase Antibody (Ab) programming strategy. The effects of the cpAbs on cellular functions related to tumor progression were examined in vitro using tumor cell lines and their cognate integrin ligands, fibronectin and osteopontin. The inhibitory functions of the conjugates and their specificity were examined based on interference with cell-cell and cell-ligand interactions related to tumor progression. Cell binding analyses of the anti-integrin cpAbs revealed high affinity for tumor cells that overexpressed αvß3 and αvß6 integrins, and weak interactions with αvß1 and αvß8 integrins, in vitro. Functional analyses demonstrated that the cpAbs strongly inhibited cell-cell interactions through osteopontin binding, and they had little or no immediate effects on cell viability and proliferation. On the basis of these characteristics, the cpAbs are likely to have a broad range of activities in vivo, as they can target and antagonize one or multiple αv integrins expressed on tumors and tumor vasculatures. Presumably, these conjugates may inhibit the establishment of metastastatic tumors in distant organs through interfering with cell adhesion more effectively than antibodies or compounds targeting one integrin only. These anti-integrin cpAbs may also provide useful reagents to study combined effect of multiple αv integrins on cellular functions in vitro, on pathologies, including tumor angiogenesis, fibrosis, and epithelial cancers, in vivo.

Multiple catalytic aldolase antibodies suitable for chemical programming.

Chemical programming of nine murine antibodies with catalytic aldolase activity was examined using compounds, equipped with diketone or pro-vinyl ketone linkers that inhibit integrin adhesion receptor functions. The results showed that most Abs were programmed using the diketone compounds in a manner similar to previously reported catalytic antibody 38C2. On the other hand, only those antibodies, which catalyzed the retro aldol reaction of the pro-vinyl ketone linkers efficiently, were programmed. Conjugated to integrin targeting compounds, at least three new antibodies, including 84G3, 85H6, and 90G8, exhibited high specific binding to human tumor cells expressing integrin alpha(v)beta(3.).

Alteration of the bis-tetrahydrofuran core stereochemistries in asimicin can affect the cytotoxicity.

A systematic analysis using 10 synthetic asimicin stereoisomers revealed that the stereochemistry of the bis-tetrahydrofuran core, including the tetrahydrofuran rings and the adjacent hydroxy functions, had significant effect on its cytotoxicity. Our findings set to rest the highly controversial perception that the stereochemistry of the tetrahydrofuran core has little effect on the activity, which is not true for its cytotoxic effect, and also reinforces the previous conclusion that asimicin is a highly potent anticancer compound.

Functional and mechanistic analyses of biomimetic aminoacyl transfer reactions in de novo designed coiled coil peptides via rational active site engineering.

Ribosomes and nonribosomal peptide synthetases (NRPSs) carry out instructed peptide synthesis through a series of directed intermodular aminoacyl transfer reactions. We recently reported the design of coiled-coil assemblies that could functionally mimic the elementary aminoacyl loading and intermodular aminoacyl transfer steps of NRPSs. These peptides were designed initially to accelerate aminoacyl transfer mainly through catalysis by approximation by closely juxtaposing four active site moieties, two each from adjacent noncovalently associated helical modules. In our designs peptide self-assembly positions a cysteine residue that is used to covalently capture substrates from solution via transthiolesterification (substrate loading step to generate the aminoacyl donor site) adjacent to an aminoacyl acceptor site provided by a covalently tethered amino acid or modeled by the epsilon-amine of an active site lysine. However, through systematic functional analyses of 48 rationally designed peptide sequences, we have now determined that the substrate loading and intermodular aminoacyl transfer steps can be significantly influenced (up to approximately 103-fold) by engineering changes in the active site microenvironment through amino acid substitutions and variations in the inter-residue distances and geometry. Mechanistic studies based on 15N NMR and kinetic analysis further indicate that certain active site constellations furnish an unexpectedly large pK(a) depression (1.5 pH units) of the aminoacyl-acceptor moiety, helping to explain the observed high rates of aminoacyl transfer in those constructs. Taken together, our studies demonstrate the feasibility of engineering efficient de novo peptide sequences possessing active sites and functions reminiscent of those in natural enzymes.