Molecular properties of the partially SDS-resistant lectin from the albumen gland of Helix pomatia and demonstration of lectin-related molecules on the surface of H. pomatia haemocytes

Abstract

Lectins (agglutinins) are components of the immunobiological recognition system of vertebrates and invertebrates. The present study focused on the molecular properties of the agglutinin from the albumen gland of Helix pomatia (HPA) and on the occurrence of lectin-related molecules on the surface of H. pomatia haemocytes. According to the current model (Hammarstrom et al., 1972, Scandinavian Journal of Immunology, 1: 259-301), the hexameric HPA of about 79 kDa is composed of three non-covalently associated dimers (26 kDa), each consisting of two disulphide-bridged 13 kDa monomers. However, on native-gradient polyacrylamide gel electrophoresis (PAGE), we obtained high molecular weight bands representing lectin polymers. The stepwise dissociation of these was achieved by incubation with SDS at temperatures from 20 to 408C (1 h) and at 1008C (10 min). The results obtained on SDS-PAGE included the occurrence of partially SDS-resistant hexamers of about 66 kDa, of two dimer bands of 22 and 19 kDa, and of two minor heteromonomer fractions. Complete dissociation into heteromonomers of 13 and 11 kDa was achieved by boiling the lectin (10 min) with SDS under reducing conditions. For native lectin molecules, both monomers occurred as disulphide-linked homodimers. Monomers or dimers electroeluted from an SDS -gel, reassociated to SDS-resistant oligomers upon re-electrophoresis. Finally, molecules antigenetically related to the lectin were extracted from the membrane of H. pomatia haemocytes. Anti-HPA antibodies recognized peptides with an apparent molecular weight of about 30 and 56 kDa, which were shown to represent cell-surface molecules.