THE ROLE OF TREHALOSE SYNTHESIS FOR THE ACQUISITION OF THERMOTOLERANCE IN YEAST .2. PHYSIOLOGICAL CONCENTRATIONS OF TREHALOSE INCREASE THE THERMAL-STABILITY OF PROTEINS IN-VITRO

In-baker's yeast (Saccharomyces cerevisiae), accumulation of the non-r educing disaccharide, trehalose, is triggered by stimuli that activate the heat-shock response. Previously, trehalose levels have been shown to be closely correlated with thermotolerance, suggesting a protectiv e function of this substance. Genetic evidence in support of this view is presented in an accompanying paper [De Virgilio, C., Hottiger, T., Dominguez, J., Boller, T. & Wiemken, A. (1993) Eur. J. Biochem. 219, 179-186]. In this study, we have examined the effect of trehalose:on t he thermal stability of proteins, a parameter thought to be a major de terminant of thermotolerance. Physiological concentrations of trehalos e (up to 0.5 M) were found to efficiently protect enzymes of yeast (gl ucose-6P-dehydrogenase, phosphoglucose-isomerase) as well as enzymes o f non-yeast origin (bovine. glutamic dehydrogenase, EcoRI) against hea t inactivation in vitro. Trehalose also reduced the heat-induced forma tion of protein aggregates. The disaccharide proved to be a compatible solute, as even at very high concentrations (up to 1 M) it did not si gnificantly interfere with the activity of test enzymes. Trehalose was at least as good of better a protein stabilizer than any of a number of other compatible solutes (including sugars, polyalcohols and amino acids), while the structurally related trehalose-6P was devoid of any protective effect. Thermoprotection of enzymes by trehalose was eviden t even in solutions containing high concentrations of yeast protein or substrate. The data-indicate that trehalose accumulation may-increase -the thermotolerance of yeast-by enhancing protein stability in intact cells.