Acid proteinase secreted by Candida tropicalis: Functional analysis of preproregion cleavages in C-tropicalis and Saccharomyces cerevisiae

The 40 kDa secreted aspartyl proteinase (Sapt1) of Candida tropicalis is a pepsin-like enzyme encoded by the SAPT1 gene. According to the deduced amino acid sequence, Sapt1 has a putative preproregion of 60 amino acids preceding the mature enzyme. Maturation and processing of Sapt1 was analysed in C. tropicalis and Saccharomyces cerevisiae strains expressing wildtype or mutated forms of SAPT1. In S. cerevisiae, the glycosylated 46 kDa proenzyme was converted to the mature 40 kDa form of Saptl by KEX2-dependent proteolytic cleavage following the Lys(59)-Arg(60) sequence. The replacement of Lys(59)-Arg(60) by Lys(59)-Gly(60) revealed that the precursor can be processed by an autocatalytic cleavage. This alternative processing pathway to produce mature Saptl is less efficient than the Kex2-mediated pathway. Finally, it was shown that in C. tropicalis and S. cerevisiae the removal of the proregion was a prerequisite for the secretion of Sapt1.