Chemo-enzymatic synthesis of bioactive glycopeptide using microbial endoglycosidase.

The chemo-enzymatic synthesis of a glycopeptide, which involves the chemical synthesis of N-acetylglucosaminyl peptide and the enzymatic transfer of oligosaccharide, is described. The first step of the chemo-enzymatic method is the chemical synthesis of N-acetylglucosaminyl peptide with an N-acetylglucosamine moiety bound to the asparaginyl residue of the peptide by a solid-phase method. The second step is transglycosylation of a complex-type oligosaccharide derived from a glycopeptide to an N-acetylglucosaminyl peptide by endo-beta-N-acetylglucosaminidase of Mucor hiemalis (Endo-M). Peptide T can block HIV infection of human T cells. We added the sialo-complex-type oligosaccharide to chemically synthesized N-acetylglucosaminyl Peptide T using the transglycosylation activity of Endo-M. The glycosylated Peptide T thus produced showed a higher degree of resistance to protease digestion than Peptide T. We also prepared calcitonin glycopeptide. Calcitonin is a calcium-regulating hormone that is widely used in therapy for hypercalcemia, and is glycosylated by the chemo-enzymatic method described above. This glycopeptide demonstrated sufficient physiological activity. Comparison of NMR data between native calcitonin and calcitonin glycopetide revealed that the glycosylation does not affect the binding topology of the peptide. N-Acetylglucosaminyl glutamine was also a good glycoside acceptor of Endo-M. We were able to add the sialo-complex-type oligosaccharide to the glutamine residue of the Substance P neuropeptide using the transglycosylation activity of Endo-M. The glycosylated Substance P was biologically active, although its activity was rather low, and stable against peptidase digestion. The oligosaccharide moiety attached to the l-glutamine residue of the peptide was not liberated by PNGase that liberated asparagine-linked oligosaccharide from glycopeptides.