Evidence for an extracellular acid proteolytic activity secreted by living cells of Saccharomyces cerevisiae PlR1: impact on grape proteins

In this work, Saccharomyces cerevisiae PlR1, a strain isolated from Pinot noir grapes in the Champagne area, was shown to secrete an acid proteolytic activity against bovine serum albumin. This proteolytic activity was detectable in cell-free culture supernatants at the beginning of the exponential growth phase and increased with yeast growth. Using a zymography method, only one protease band with a molecular mass of 72 kDa was observed. This extracellular proteolytic activity was detected in the pH range from 2 to 4 with a maximal value at pH 2.5 and 38 °C and was completely inhibited by pepstatin A. The secretion of this protease did not need any protein inducer and seemed to be insensitive to nitrogen catabolic repression. S. cerevisiae PlR1 was also able to secrete this proteolytic activity during alcoholic fermentation, and it was found to be active against grape proteins, with a molecular mass around 25 kDa, at optimal conditions of 38 °C, pH 3.5.