Title : New type of linkage between
a carbohydrate and a
protein: C-glycosylation of a specific
tryptophan residue in human
RNase Us
Abstract :
- We report a new type of linkage between a carbohydrate and a protein, involving the rarely modified side chain of a tryptophan residue
- An aldohexopyranosyl residue was found to be linked via a C-C bond to the indole ring of the tryptophan residue at position 7 of human RNase Us
- Mass spectrometric analysis of peptides containing this residue showed a molecular mass 162 Da higher than that expected for tryptophan
- The fragmentation pattern of the modified amino acid side chain was reminiscent of that of aromatic C-glycosides, suggesting a direct attachment of a hexose residue to a C- position of the tryptophan indole moiety
- 1H and 13C NMR spectroscopic data confirmed this inference and unequivocally demonstrated the substituent to be an aldohexopyranosyl residue , C-glycosidically linked to the C2 atom of the indole
- This mode of attachment differs from the ones known so far, in which carbohydrates are linked to an amino acid side chain by N- or O-glycosidic bonds