A strategy for probing the autonomy of cross-domain stereochemical communication in glycoconjugates

Chemical synthesis of highly congested gp120 V1V2 N-glycopeptide antigens for potential HIV-1-directed vaccines

Critical to the search for an effective HIV-1 vaccine is the development of immunogens capable of inducing broadly neutralizing antibodies (BnAbs). A key first step in this process is to design immunogens that can be recognized by known BnAbs. The monoclonal antibody PG9 is a BnAb that neutralizes diverse strains of HIV-1 by targeting a conserved carbohydrate-protein epitope in the variable 1 and 2 (V1V2) region of the viral envelope. Important for recognition are two closely spaced N-glycans at Asn(160) and Asn(156). Glycopeptides containing this synthetically challenging bis-N-glycosylated motif were prepared by convergent assembly, and were shown to be antigenic for PG9. Synthetic glycopeptides such as these may be useful for the development of HIV-1 vaccines based on the envelope V1V2 BnAb epitope.

Recent Departures in the Synthesis of Peptides and Glycopeptides

In this account, we describe the results of a research program directed to the proposition that chemical synthesis can play a valuable role in identifying biologic level molecules worthy of pharma level development. We recount our journey towards the chemical synthesis of homogeneous erythropoietin, the challenges we encountered, and our efforts to address deficiencies in the current "state of the art" of glycopeptide synthesis. Here we describe new methods for the synthesis of glycopeptides that have emerged from the erythropoietin adventure, including the development of unique C-terminal acyl donors, novel amide bond forming methods, and new ligation and coupling strategies.

Carbohydrate post-glycosylational modifications

Carbohydrate modification is a common phenomenon in nature. Many carbohydrate modifications such as some epimerization, O-acetylation, O-sulfation, O-methylation, N-deacetylation, and N-sulfation, take place after the formation of oligosaccharide or polysaccharide backbones. These modifications can be categorized as carbohydrate post-glycosylational modifications (PGMs). Carbohydrate PGMs further extend the complexity of the structures and the synthesis of carbohydrates and glycoconjugates. They also increase the capacity of the biological regulation that is achieved by finely tuning the structures of carbohydrates. Developing efficient methods to obtain structurally defined naturally occurring oligosaccharides, polysaccharides, and glycoconjugates with carbohydrate PGMs is essential for understanding the biological significance of carbohydrate PGMs. Combined with high-throughput screening methods, synthetic carbohydrates with PGMs are invaluable probes in structure-activity relationship studies. We illustrate here several classes of carbohydrates with PGMs and their applications. Recent progress in chemical, enzymatic, and chemoenzymatic syntheses of these carbohydrates and their derivatives are also presented.

The interplay of glycosylation and disulfide formation influences fibrillization in a prion protein fragment

It is now accepted that the structural transition from cellular prion protein (PrPC) to proteinase K-resistant prion protein scrapie (PrPSc) is the major event leading to transmissible spongiform encephalopathies. Although the mechanism of this transition remains elusive, glycosylation has been proposed to impede the PrPC to PrPSc conversion. To address the role of glycosylation, we have prepared glycosylated and unglycosylated peptides derived from the 175-195 fragment of the human prion protein. Comparison of the structure, aggregation kinetics, fibril formation capabilities, and redox susceptibility of Cys-179 has shown that the N-linked glycan (at Asn-181) significantly reduces the rate of fibrillization by promoting intermolecular disulfide formation via Cys-179. Further-more, the aggressive fibrillization of a C179S mutant of this fragment highlights the significant role of disulfide stability in retarding the rate of fibril formation. The implications of these studies are discussed in the context of fibril formation in the intact prion protein.

Homogeneous glycopeptides and glycoproteins for biological investigation

Protein glycosylation is widely recognized as a modulator of protein structure, localization, and cell-cell recognition in multicellular systems. Glycoproteins are typically expressed as mixtures of glycoforms, their oligosaccharides being generated by a template-independent biosynthetic process. Investigation of their function has been greatly assisted by sources of homogeneous material. This review summarizes current efforts to obtain homogeneous glycopeptide and glycoprotein materials by a variety of methods that draw from the techniques of recombinant expression, chemical synthesis, enzymatic transformation, and chemoselective ligation. Some of these techniques remove obstacles to glycoprotein synthesis by installing nonnative linkages and other modifications for facilitated assembly. The end purpose of the described approaches is the production of glycosylated materials for experiments relevant to the biological investigation of glycoproteins, although the strategies presented apply to other posttranslational modifications as well.