The hexopyranosyl residue that is C-glycosidically linked to the side chain of tryptophan-7 in human RNase Us is α-mannopyranose

Abstract

Recently, the novel C-glycosidic linkage of a hexopyranosyl residue to the indole ring of tryptophan residue 7 of human RNase Us was reported [Hofsteenge, J., Muller, D. R., de Beer, T., Loffler, A., Richter, W. J., & Vliegenthart, J. F. G. (1994) Biochemistry 33, 13524-135301. Identification of this monosaccharide is a prerequisite for studies of its biosynthesis and its biological relevance. Using vicinal proton-proton coupling constants and rotating-frame nuclear Overhauser enhancements, we demonstrate that the C-linked substituent is a-mannopyranose. Furthermore, the nuclear magnetic resonance (NMR) data indicate that the mannopyranose moiety in a glycopeptide derived from RNase Us adopts several conformations on the NMR time scale.