Identification of histidine residues in the sugar binding site of snake gourd (Trichosanthes anguina) seed lectin.

摘要

Chemical modification studies were used to identify the amino acid side chains involved in the saccharide-binding activity of snake gourd (T. anguina [T. cucumerina]) seed lectin (SGSL). Modification of the side chain amino groups of lysine residues, hydroxyl groups of tyrosine residues and the thiol groups of cysteine residues did not alter the agglutinating activity of SGSL. However, modification of the imidazole side chains of histidyl residues of SGSL completely inhibited its haemagglutinatingactivity. Presence of galactose resulted in partial protection of the modification reaction. Modification of histidine residues was reversed either by treating histidine-modified lectin with hydroxylamine or by incubating the sample at 37deg C for 2 h. It is suggested that histidine side chains are directly involved in the carbohydrate-binding and haemagglutinating activities of SGSL.