title: A structural comparison of the A and B subunits of Griffonia simplicifolia I isolectins.
abstract: A structural comparison between the A and B subunits of the five tetrameric Griffonia simplicifolia I isolectins (A4, A3B, A2B2, AB3, B4) was undertaken to determine the extent of homology between the subunits. The first 25 N-terminal amino acids of both A and B subunits were determined following the enzymatic removal of N-terminal pyroglutamate blocking groups with pyroglutamate aminopeptidase. Although 21 amino acids were common to both subunits, there were four unique amino acids in the N-terminal sequence of A and B. Residues 8, 9, 17, and 19 were asparagine, leucine, lysine, and asparagine in subunit A and threonine, phenylalanine, glutamic acid, and serine in subunit B. The last six C-terminal amino acids, released by digestion with carboxypeptidase Y, were the same for both subunits: Arg-(Phe, Val)-Leu-Thr-Ser-COOH. Subunit B, which contains one methionyl residue, was cleaved by cyanogen bromide into two fragments, a large (Mr = 31,000) and a small (Mr = 2700) polypeptide. Failure of the small fragment to undergo manual Edman degradation indicated an N-terminal blocking group, presumably pyroglutamate. Both subunits were digested with trypsin and the tryptic peptides were analyzed using reverse-phase HPLC. Tryptic glycopeptides were identified by labeling the carbohydrate moiety of the A and B subunit using sodium [3H] borohydride. Cysteine-containing tryptic peptides were similarly identified by using [1-14C]iodoacetamide. Approximately 30% of the tryptic peptides were common to both subunits. Thus, although the N- and C-terminal regions of A and B are similar, the subunits each possess unique sequences.
mesh_terms: D000595:Amino Acid Sequence; D002268:Carboxypeptidases; D002851:Chromatography, High Pressure Liquid; D003488:Cyanogen Bromide; D037102:Lectins; D046911:Macromolecular Substances; D008970:Molecular Weight; D010446:Peptide Fragments / Q000302:isolation & purification; D011751:Pyroglutamyl-Peptidase I; D014357:Trypsin
chemical_list: D037102:Lectins; D046911:Macromolecular Substances; D010446:Peptide Fragments; D002268:Carboxypeptidases; C022633:serine carboxypeptidase; D011751:Pyroglutamyl-Peptidase I; D014357:Trypsin; D003488:Cyanogen Bromide