INFLUENCE OF CORE FUCOSYLATION ON THE FLEXIBILITY OF A BIANTENNARY N-LINKED OLIGOSACCHARIDE

Fluorescence energy transfer was used to study the conformation of eac h antenna of a complex biantennary oligosaccharide. A core fucosylated biantennary oligosaccharide was converted to a glycosylamine which al lowed coupling of a naphthyl donor fluorophore directly to the reducin g-end GlcNAc 1. After generating an aldehyde at C-6 of residue 6 or 6' using galactose oxidase, a dansyl ethylenediamine acceptor fluorophor e was coupled to either antenna of the oligosaccharide resulting in tw o donor-acceptor pairs. [GRAPHICS] The fluorescence properties of the naphthyl group allowed determination of the end-to-end donor-acceptor distance and antenna flexibility of each isomer by steady-state and ti me-resolved fluorescence energy transfer at temperatures ranging from 0 to 40 degrees C. Extended(20.6 Angstrom) and folded (11.4 Angstrom) donor-acceptor distance populations were identified for the isomer con taining dansyl attached to Gal 6', whereas only a single extended popu lation (19.7 Angstrom) was determined when dansyl was attached to Gal 6. The presence of Fuc 1' had a dramatic effect on the conformation of the 6' antenna, Temperature modulation failed to alter the ratio of e xtended/folded populations when fucose was present. However, following the removal of fucose, the ratio of the extended/folded populations f or 6' exhibited a temperature dependent conformational equilibrium all owing calculation of the enthalpy and entropy of unfolding. These resu lts established a unique conformational property for the 6' antenna of a biantennary oligosaccharide that is influenced by core fucosylation . Comparison of the results obtained for the 6 antenna of biantennary with previous fluorescence energy transfer studies on a triantennary g lycopeptide also established conformational differences in this antenn a which are dependent on oligosaccharide structure.