A secreted serine protease of Paracoccidioides brasiliensis and its interactions with fungal proteins

Abstract

Abstract Background Paracoccidioides brasiliensis is a thermodimorphic fungus, the causative agent of paracoccidioidomycosis (PCM). Serine proteases are widely distributed and this class of peptidase has been related to pathogenesis and nitrogen starvation in pathogenic fungi. Results A cDNA (Pb sp) encoding a secreted serine protease (Pb SP), was isolated from a cDNA library constructed with RNAs of fungal yeast cells recovered from liver of infected mice. Recombinant Pb SP was produced in Escherichia coli, and used to develop polyclonal antibodies that were able to detect a 66 kDa protein in the P. brasiliensis proteome. In vitro deglycosylation assays with endoglycosidase H demonstrated that Pb SP is a N-glycosylated molecule. The Pb sp transcript and the protein were induced during nitrogen starvation. The Pb sp transcript was also induced in yeast cells infecting murine macrophages. Interactions of Pb SP with P. brasiliensis proteins were evaluated by two-hybrid assay in the yeast Saccharomyces cerevisiae. Pb SP interacts with a peptidyl prolyl cis-trans isomerase, calnexin, HSP70 and a cell wall protein PWP2. Conclusions A secreted subtilisin induced during nitrogen starvation was characterized indicating the possible role of this protein in the nitrogen acquisition. Pb SP interactions with other P. brasiliensis proteins were reported. Proteins interacting with Pb SP are related to folding process, protein trafficking and cytoskeleton reorganization.