CONSERVATION OF RAPID 2-STATE FOLDING IN MESOPHILIC, THERMOPHILIC ANDHYPERTHERMOPHILIC COLD SHOCK PROTEINS

The cold shock protein CspB from Bacillus subtilis is only marginally stable, but it folds extremely fast in a simple N reversible arrow U t wo-state reaction. The corresponding cold shock proteins from the ther mophile Bacillus caldolyticus and the hyperthermophile Thermotoga mari tima show strongly increased conformational stabilities, but unchanged very fast two-state refolding kinetics. The absence of intermediates in the folding of B. subtilis CspB is thus not a corollary of its low stability. Rather, two-state folding and an unusually native-like acti vated state of folding seem to be inherent properties of these small a ll-beta proteins. There is no link between stability and folding rate, and numerous sequence positions exist which can be varied to modulate the stability without affecting the rate and mechanism of folding.