The positions of the disulfide bonds and the glycosylation site in a lectin of the acorn barnacle Megabalanus rosa

Abstract

The positions of the interchain and intrachain disulfide bonds and the glycosylation site in a lectin of the acorn barnacle Megabalanus rosa were determined. The lectin ( M r 140000 ) is composed of the same subunit ( M r 22000 ) which is cross-linked by disulfide bonds to form a dimer. Intact lectin yielded two fragments, CB1 and CB2, by cleavage with cyanogen bromide. One intrachain and two interchain disulfide bonds were identified as Cys-53-Cys-61, Cys-14-Cys-50′ and Cys-50-Cys-14′, respectively, by enzymatic digestion and Edman degradation of CB1. Two interchain disulfide bonds were determined as Cys-78-Cys-168 and Cys-144-Cys-160 by enzymatic digestion of CB2. The two interchain disulfide bonds are well conserved through all invertebrate lectins and calcium-dependent animal lectins. S- Carboxaminodomethylated lectin was digested with Staphylococcus aureus V8 proteinase and separated by reversed-phase HPLC. Glycopeptides were detected by the 4-N,N- dimethylamino-4′- azobenzene sulfonyl hyrazide method. Sequence analyses of the glycopeptides showed that a carbohydrate chain attached to Asn-39.