SOLUTION CONFORMATIONS OF A BIANTENNARY GLYCOPEPTIDE AND A SERIES OF ITS EXOGLYCOSIDASE PRODUCTS FROM SEQUENTIAL TRIMMING OF SUGAR RESIDUES

Linkages between sugar residues in branched oligo saccharides exhibit various degrees of flexibility. This flexibility, together with other forces, determines the overall solution conformation of oligosaccharid es. We used the method of time-resolved resonance energy transfer to s tudy the solution conformations of a biantennary glycopeptide and its partially trimmed products by exoglycosidases. The N-terminal of the g lycopeptide was labeled with 2-naphthyl acetic acid as a fluorescent d onor. Either terminal sugar residue, Gal6', on the branch bearing 6-li nked Man (antenna 6'), or Neu5Ac on the branch bearing 3-linked Man (a ntenna 6) was labeled with 5-dimethylaminonaphthalene-1-sulfonyl as an acceptor. The distance and distance distributions between the termina ls were measured. In the intact biantennary glycopeptide, the donor-ac ceptor distance distribution of antenna 6' is bimodal with a majority of the population in the extended conformation and that of antenna 6 i n one very broad population. The Neu5Ac on antenna 6 is oriented towar d the N-terminal at low temperature and adopts a more extended form at high temperature. The removal of individual sugar residues along one of the two antenna in the biantennary oligosaccharide has a small effe ct on the distance distribution of the remaining antenna for both ante nnae 6 and 6'. Together with previous studies of the triantennary glyc opeptides (Rice, K. G., Wu, P. G., Brand, L., and Lee, Y. C. (1993) Bi ochemistry 32, 7264-7270), our results suggest that both steric hindra nce and inter-residue hydrogen bonding are very important in the foldi ng pattern in oligosaccharide structures.