Isolation and Characterization of a cDNA Clone Encoding a Lectin Gene from Agaricus bisporus

Aguricus bisporus, the common commercial golden white mushroom, has been reported to have between two and four hemagglutinin proteins (ABAS) (Presant and Kornfeld, 1972; Ahmad et al., 1984; Sueyoshi et al., 1985). These lectins, which differ in their pIs, have been purified and characterized. They exist as tetramers of mo1 wt 58,000 to 64,000, composed of identical subunits of mo1 wt 16,000 (Sueyoshi et al., 1985; Presant and Kornfeld, 1972). Isolectins often either reflect heterogeneity of posttranslational modification or may be products of different genes (Van Damme and Peumans, 1987; Van Damme et al., 1991; Zenteno et al., 1991). Like many lectins, those from Aguricus have been reported to be glycosylated (Ahmad et al., 1984). A11 ABA isoforms have similar carbohydrate binding specificities and binding is not inhibited by simple monosaccharides. Many lectins are useful as probes for differentiating between normal and malignant cell surfaces. The availability of lectin genes may allow design of hybrid genes whose products would have useful applications. Here we describe the cloning of a cDNA for ABA (Table I). Southern blot analysis indicated that at least two ABA genes were present. The sequences of the three cDNA clones isolated were identical. N-terminal amino acid sequence information for the four ABA isolectins indicated that a11 were identical for their first 21 amino acids. Potentia1 O-glycosylation sites were identified at Thr”, Ser’, and Sers8 because none gave standard elution profiles during phenylthiohydantoin-amino acid separations. Only one consensus N-glycosylation site was found (Asp8*); however, peptide sequencing through this region gave a normal Asp signal. The amino acid composition deduced from the cDNA sequence is very similar to that reported for the isolectins except that Ile, Ser, and Pro were previously underestimated (Sueyoshi et al., 1985).