Life in the pressure cooker: The thermal unfolding of proteins from hyperthermophiles

Abstract Xieported here are the first results of a qcantitative ther-modynamic st-dy involvixg a series of proteins isolated from the anaerobic sulfur-reducixg archaebacterium Pyrococcus furiosus which grows near submrize geotherml vents on the deep ocean floor. The proteins isolated and investigated here are the two non-henie iron proteins rubredoxin (Kid 5400), and ferredoxin (Mw 7 5 0 0) , and the er-zyine glutamate dehydrogeriase GDH (Xw 270000). The enzyme is inactive at 4OoC and fully activated at 3 0 OC. Independent of their particular primary structure ax! independent of the molecular weight (Mw) all three proteins investigated unfold at exactly the same temperature (113OC) The experimentally observed transition temperature Tm coincides with the extrapolated conversion temperature T * (Privalov, Privalov & Gill, Murphy and Gill, lreire and Murphy, 1-4) of 112OC. It is readily accepted that at this temperature the hydrophobic interactions will cease to contribute to the overall stability of the ordered secondary and/or tertiary structure causing the core of any globular protein to unfold to the denatured state. Thus 1 1 3 O C seems to be the threshold temperature for sustantation of life on earth