Isolation and characterization of two chitinase-encoding genes ( cts1, cts2) from the fungus Coccidioides immitis

Abstract

Two chitinase(CTS)-encoding genes ( cts) from Coccidioides immitis (CI), a respiratory fungal pathogen of humans, were cloned and sequenced. Both the genomic and cDNA sequences are presented. The transcription start points and poly(A)-addition sites were confirmed. The cts1 gene contains five introns and a 1281-bp ORF which translates a 427-amino-acid (aa) protein of 47.4 kDa. The cts2 gene contains two introns and a 2580-bp ORF which translates a 860-aa protein of 91.4 kDa. The deduced CTS1 protein showed highest homology to the Aphanocladium album and Trichoderma harzianum CTS (74% and 76%, respectively), while CTS2 showed highest homology to the CTS of Saccharomyces cerevisiae (Sc) and Candida albicans (47% and 51%, respectively). The putative N-terminal sequence of the mature CTS1 protein also showed 89% homology to the reported N-terminal sequence of a 48-kDa complement fixation antigen (CF-Ag) of Ci which has demonstrated chitinase activity. The CFAg is a clinically important antigen used in serodiagnosis of this fungal disease. CTS2 showed several of the conserved features of the Sc CTS, including putative catalytic and Ser/Thr-rich domains, and a C-terminal Cys-rich region. We propose that CTS1 and CTS2 of Ci are members of two distinct classes of fungal chitinases, an observation not previously reported for a single fungus.