We report a study on the adaptive response of a wild-type wine Saccharomyces cerevisiae strain, isolated from natural spontaneous grape must, to mild and progressive physiological stresses due to fermentation. We observed by two-dimensional electrophoresis how the yeast proteome changes during glucose exhaustion, before the cell enters its complete stationary phase. On the basis of their identification, the proteins representing the S. cerevisiae proteomic response to fermentation stresses were divided into three classes: repressed proteins, induced proteins and autoproteolysed proteins. In an overall view, the proteome adaptation of S. cerevisiae at the time of glucose exhaustion seems to be directed mainly against the effects of ethanol, causing both hyperosmolarity and oxidative responses. Stress-induced autoproteolysis is directed mainly towards specific isoforms of glycolytic enzymes. Through the use of a wild-type S. cerevisiae strain and PMSF, a specific inhibitor of vacuolar proteinase B, we could also distinguish the specific contributions of the vacuole and the proteasome to the autoproteolytic process.
Abbreviations used: 2D, two-dimensional; Hsp26 (etc.), heat-shock protein 26 (etc.); YPD, yeast peptone dextrose.