CARBOHYDRATE PROTECTION OF ENZYME STRUCTURE AND FUNCTION AGAINST GUANIDINIUM CHLORIDE TREATMENT DEPENDS ON THE NATURE OF CARBOHYDRATE AND ENZYME

Baker's yeast cells accumulate osmolytes as a response to several stre ss conditions such as high-temperature and low-temperature shifts, deh ydration, or osmotic stress. One of the major osmolytes that accumulat es is trehalose, which plays an essential role affecting the survival of yeast at the time of stress. In this report, we show that trehalose efficiently protects the function and the structure of two yeast cyto solic enzymes against chemical denaturation by guanidinium chloride. O ther sugars tested also protected yeast pyrophosphatase and glucose-6- phosphate dehydrogenase structure against guanidinium chloride effects , but were not as efficient at protecting enzyme activity. The thermos table pyrophosphatase from Bacillus stearothermophilus was also protec ted by several sugars against the chaotropic properties of guanidinium chloride, but was only protected by trehalose against functional inac tivation. The function of the membrane-embedded H+-ATPase from yeast c ould not be protected by any of the tested sugars, although all of the sugars protected its structure from guanidinium-chloride-induced unfo lding. The results presented in this study suggest that several sugars are able to prevent protein unfolding induced by a chaotropic compoun d. However, prevention of functional inactivation depends on the natur e of the sugar. Trehalose was the most efficient, being able to protec t many cytosolic enzymes against guanidinium chloride. The efficiency of protection also depended on the nature of the protein tested. This might explain why trehalose is one of the osmolytes accumulated in yea st and also why it is not the only osmolyte to accumulate.