Cloning and expression of a gene encoding an integrin-like protein in Candida albicans

Abstract

The existence of integrin-like proteins in Candida albicans has been postulated because monoclonal antibodies to the leukocyte integrins αM and αX bind to blastospores and germ tubes, recognize a candidal surface protein of κ 185 kDa, and inhibit candidal adhesion to human epithelium. The gene αINT1 was isolated from a library of C. albicans genomic DNA by screening with a cDNA probe from the transmembrane domain of human αM. The predicted polypeptide (αInt1p) of 188 kDa contains several motifs common to αM and αX: a putative I domain, two EF-hand divalent cation-binding sites, a transmembrane domain, and a cytoplasmic tail with a single tyrosine residue. An internal RGD tripeptide is also present. Binding of anti-peptide antibodies raised to potential extracellular domains of αInt1p confirms surface localization in C. albicans blastospores. By Southern blotting, αINT1 is unique to C. albicans. Expression of αINT1 under control of a galactose-inducible promoter led to the production of germ tubes in haploid Saccharomyces cerevisiae and in the corresponding ste12 mutant. Germ tubes were not observed in haploid yeast transformed with vector alone, in transformants expressing a galactose-inducible gene from Chlamydomonas, or in transformants grown in the presence of glucose or raffinose. Transformants producing αInt1p bound an anti-αM monoclonal antibody and exhibited enhanced aggregation. Studies of αInt1p reveal novel roles for primitive integrin-like proteins in adhesion and in STE12-independent morphogenesis.