Dr. Daniel E. Kahne will be supported as a Presidential Young Investigator by the Organic Synthesis Program. He will be studying how the attachment of carbohydrates to a peptide alters its structure and in so doing modulates the biological activity. New methods of synthesizing glycopeptides will be developed in order to facilitate the necessary structure-function studies. The first step involves working out strategies to synthesize glycopeptides. Currently a glycosylation method is being developed that can be used to attach sugars to amino acids rapidly and in good yield. Glycopeptides will be incorporated using solid phase synthesis. This will primarily involve manipulation of protecting group schemes so that the carbohydrate moiety can be deprotected and the glycopeptide cleaved from the resin without hydrolysis of glycosidic bonds. The glycopeptide sequences will have been chosen from systemswhere there is evidence that the carbohydrate induces a conformational change in the peptide. Initial studies will be confined to peptide sequences of six to eight amino acids. Proton NMR will be used to compare the structure of the glycopeptide with its nonglycosylated analogue to evaluate the effects of the attached carbohydrate. Assignments and coupling constants can be obtained from homonuclear (phase-sensitive) and heteronuclear correlation spectroscoyy. Through-space interactions (dipolar coupling) obtained from NOESY or spin-locked (transverse) NOE spectroscopy will give information about the solution conformations. Additional information about conformational structure and dynamics can be obtained by measuring amide exchange rates and relaxation times. The studies should begin to give a better understanding of how attached carbohydrates can modulate secondary structure in glycosylated regions of proteins.
