The amino acid sequence of an atypical single‐chain lectin from seeds of <i>Lathyrus sphaericus</i> (Retz)

Abstract

The major lectin from seeds of Lathyrus spaericus (Retz) was purified by fractional precipitation with (NH 4 ) 2 SO 4 , affinity chromatography on Sephadex G‐100, chromatofocusing on PBE 94 and gel filtration on Biogel P‐100 in the presence of 6 M guanidine HCl. The protein was found to be atypical of the lectins found in the Vicieae in that it was a dimer of two identical single polypeptide chains whose monomer molecular mass was estimated to be 27–28 kDa by SDS‐PAGE. The complete amino acid sequence of the monomer was determined by analysis of peptides derived from the protein by digestion with trypsin, chymotrypsin, pepsin, the S.aureus V8 protease and a lysine‐specific protease from Lysobacter enzymogenes , as well as fragments produced by cleavage with iodosobenzoic acid. The polypeptide chain contained 244 amino acids and exhibited overlapping homology with the β (heavy) and α (light) chains of the two‐chain lectins found in other Lathyrus species and in genera belonging to the tribe Vicieae, but was unusual in containing additional amino acids at the N‐terminus and in two other regions (insertions), some deletions, and alterations in 44 previously conserved amino acid positions.