Structures of sugar chains of abrin a obtained from Abrus precatorius seeds

The amino acid sequences around the glycosylation sites and the structures of the sugar chains of abrin a (a lectin derived from Abrus precatorius) were determined. Two glycopeptides were isolated from pronase digests of the B-chain of abrin a after gel filtration and ion-exchange chromatography. The amino acid sequences of these glycopeptides were determined to be Asp-Asn(CHO)-Gly-Thr and Gly-Asn(CHO)-Asn. The sugar chains of each glycopeptide were liberated by hydrazinolysis and then free amino groups were N-acetylated. The reducing-end residues were coupled with 2-aminopyridine and the resulting pyridylamino (PA-) derivatives of sugar chains were purified by reversed-phase HPLC. The structures of the purified PA-sugar chains were estimated by component analysis, comparison of elution positions with those of standard PA-sugar chains by two kinds of HPLC (Hase, S. et al. (1986) J. Biochem. 100, 1-100), stepwise exoglycosidase digestions, and partial acetolysis. Abrin a was shown to contain the following sugar chains. {A figure is presented}.