Conformational transitions in N-linked oligosaccharides

Abstract

An assignment strategy involving 1H-1H correlated spectroscopy (COSY), relayed correlation spectroscopy (RECSY), nuclear Overhauser effect spectroscopy (NOESY). and triple quantum filtered correlated spectroscopy (TQCOSY) is described for six related N-linked oligosaccharides. These are of three "types", i.e., complex, bisected complex, and oligomannose. Using spin-spin coupling constant data derived from these assignments, together with semiempirical quantum mechanical energy calculations, we have examined the rotamer distributions at the Man.alpha.1-6Man.beta.-linkage in each structure, and additionally at the Man.alpha.1-6Man.alpha.-linkage in oligomannose oligosaccharides. We show that while several primary sequence differences are "passive", certain key residues modulate the orientation of the .alpha.1-6 arms. These residues may be proximal or distal to the site of the conformational change. There is no direct correlation between these perturbations and the oligosaccharide type. These data are discussed in terms of the proposed recognition fucntion of oligosaccharides in biological systems.