Compatible solutes, as defined by Brown [1], are part of a general response to environmental osmotic changes by mesophilic microorganisms. In recent years, investigation on the response of thermophiles and hyperthermophiles to osmotic and temperature stress have led to the identification of novel organic solutes [2]. There is a growing body of evidence for the role played by these unusual organic solutes (hypersolutes) in adaptation to thermophily [2]. Diglycerol phosphate is a solute that accumulates under salt stress in the hyperthermophilic archaeon Archaeoglobus fulgidus [3]. Both the optically active and the optically inactive (racemic) forms of the compound were synthesized, and the ability of the solute to act as a protecting agent against thermal denaturation was tested on several proteins. Diglycerol phosphate exerted a considerable stabilizing effect against thermal inactivation of rabbit muscle lactate dehydrogenase, baker's yeast alcohol dehydrogenase and T. litoralis glutamate dehydrogenase. Highly homologous rubredoxins from Desulfovibrio gigas, Desulfovibrio desulfuricans (ATCC 27774) and Clostridium pasteurianum were examined for their thermal stabilities at 90oC in the presence or absence of diglycerol phosphate, glycerol and inorganic phosphate [4]. These proteins showed different intrinsic thermostability and half-lives in the range 30 to 100 min. Diglycerol phosphate exerted a strong protecting effect with 3 to 4-fold increase in the half-lives for the loss of the visible spectra of D. gigas and C. pasteurianum rubredoxins. In contrast, the stability of D. desulfuricans rubredoxin was not significantly affected by diglycerol phosphate. The data show that diglycerol phosphate is a potentially useful protein stabilizer in biotechnological applications.

[1] Brown, A. D. 1976. Microbial water stress. Bacteriol. Rev. 40:803-846.

[2] Santos, H., and M. S. da Costa. 1999. Unusual organic solutes from thermophiles and hyperthermophiles. Meth. Enzymol., in press.

[3] Martins, L. O., R. Huber, H. Huber, K. O. Stetter, M. S. da Costa, and H. Santos. 1997. Organic solutes in hyperthermophilic archaea. Appl. Environ. Microbiol. 63:896-902.

[4] Sieker, L. C., R. E. Stenkamp, L. H. Jensen, B. Prickril, and J. LeGall. 1986. Struture of rubredoxin from the bacterium Desulfovibrio desulfuricans. FEBS Lett. 208:73-76.