Dehydration of yeast: Changes in the intracellular content of Hsp70 family proteins

Yeast is known to experience in natural and industrial conditions cycles of dehydration–rehydration. Several molecular mechanisms can be triggered in response to this and other environmental stressors and to rescue yeast cells of the cytotoxic effect. Since heat shock proteins constitute one of the most important systems of the response to stress we studied whether the pre-induced major stress protein, Hsp70, can cope with yeast cell drying. To induce Hsp70 expression the cells of two yeast species, Saccharomyces cerevisiae and Debaryomyces hansenii, were subjected to non-lethal heat shock. It was found that during yeast culture growth Hsp70 accumulation occurred at the exponential growth phase, and there was no marked change in the protein level at the stationary phase both in aerobic and anaerobic conditions. Interestingly, dehydration of sensitive to this kind of stress S. cerevisiae grown in anaerobic conditions led to the increase of Hsp70 expression; to our knowledge this finding was presented for the first time. Dehydration of yeast taken from the stationary growth phase did not cause the induction of Hsp70 expression. Irrespective of the inducer, Hsp70 did not rescue yeast cells from dehydration stress damages. This result well coincides with data of other groups found that Hsp70 in yeast possesses chaperonic activity, and the latter does not impact to an increase in protective power of the protein demonstrated in many other organisms.