CLONING AND EXPRESSION OF A GENE ENCODING AN INTEGRIN-LIKE PROTEIN INCANDIDA-ALBICANS

The existence of integrin-like proteins in Candida albicans has been p ostulated because monoclonal antibodies to the leukocyte integrins alp ha M and alpha X bind to blastospores and germ tubes, recognize a cand idal surface protein of approximate to 185 kDa, and inhibit candidal a dhesion to human epithelium. The gene alpha/NT1 was isolated from a li brary of C. albicans genomic DNA by screening with a cDNA probe from t he transmembrane domain of human alpha M. The predicted polypeptide (a lpha Int1p) of 188 kDa contains several motifs common to alpha M and a lpha X: a putative I domain, two EF-hand divalent cation-binding sites , a transmembrane domain, and a cytoplasmic tail with a single tyrosin e residue. An internal RGD tripeptide is also present. Binding of anti -peptide antibodies raised to potential extracellular domains of alpha Int1p confirms surface localization in C. albicans blastospores. By S outhern blotting, alpha INT1 is unique to C. albicans. Expression of a lpha INT1 under control of a galactose-inducible promoter led to the p roduction of germ tubes in haploid Saccharomyces cerevisiae and in the corresponding ste12 mutant. Germ tubes were not observed in haploid y east transformed with vector alone, in transformants expressing a gala ctose-inducible gene from Chlamydomonas, or in transformants grown in the presence of glucose or raffinose, Transformants producing alpha In t1p bound an anti-alpha M monoclonal antibody and exhibited enhanced a ggregation. Studies of alpha Int1p reveal novel roles for primitive in tegrin-like proteins in adhesion and in STE12-independent morphogenesi s.