Cloning and expression of the gene which encodes a tube precipitin antigenand wall-associated beta-glucosidase of Coccidioides immitis

We report the structure and expression of the Coccidioides immitis BGL2 gen e,which encodes a previously characterized 120-kDa glycoprotein of this fun gal respiratory pathogen. The glycoprotein is recognized by immunoglobulin M tube precipitin (TP) antibody present in sera of patients with coccidioid omycosis, a reaction which has been used for serodiagnosis of early coccidi oidal infection. The deduced amino acid sequence of BGL2 shows 12 potential N glycosylation sites and numerous serine-threonine-rich regions which cou ld function as sites for O glycosylation. In addition, the protein sequence includes a domain which is characteristic of family 3 glycosyl hydrolases. Earlier biochemical studies of the purified 120-kDa TP antigen revealed th at it functions as a beta -glucosidase (EC 3.2.1.21). Its amino acid sequen ce shows high homology to several other reported fungal beta -glucosidases which are members of the family 3 glycosyl hydrolases. Results of previous studies have also suggested that the 120-kDa beta -glucosidase participates in wall modification during differentiation of the parasitic cells (spheru les) of C. immitis. In this study we showed that expression of the BGL2 gen e is elevated during isotropic growth of spherules and the peak of wall ass ociated BGL2 enzyme activity correlates with this same phase of parasitic c ell differentiation. These data support our hypothesis that the 120-kDa bet a -glucosidase plays a morphogenetic role in the parasitic cycle of C. immi tis.