Role of Lectin in the Pea-Rhizobium Symbiosis

Abstract

Pea lectin (Pisum sativum lectin, Psl) is a 49 kDa protein with two high affinity binding sites for oligosaccharides containing a trimannoside core with a neighbouring fucosyl-α- 1,6-N-acetylglucosamine group (Kornfeld et al 1981, Debray et al 1981). Psl is a tetramer and can dissociate into two a subunits and two β subunits with molecular weights of 5800 Da and 17 000 yDa, respectively (Trowbridge 1974). Amino acid residues in one αβ-subunit pair contribute to the structure of one sugar-binding site (Van Driessche 1988). Psl is encoded by a family of four genes of which only one gene appears to be functional (Kaminski et al 1987). The sequence of the functional psl gene (LecA, Gatehouse et al 1987; Psll, Kaminski et al 1987) corresponds with the nucleotide sequence of cloned DNA complementary to Psl mRNA (Higgins et al 1983a). Furthermore, the deduced amino acid sequences correspond with previously reported amino acid sequences of parts of Psl (Van Driessche et al 1976, Foriers et al 1977, Richardson et al 1978). Psl is synthesized as a single translation product and post- translational cleavage of the Psl precursor yields one α and one β subunit (Higgins et al 1983a, 1983b, Lauwereys et al 1983, Van Driessche et al 1988).