Conformational lability of two molecular chaperones Hsc70 and gp96: effects of pH and temperature.

Hsc70 and gp96 are two heat shock proteins with molecular chaperone and immune-related activities. The dynamic conformational properties of heat shock proteins appear to play a critical role in their biological activities. In this study, we investigated the effects of pH and temperature on the conformational states of Hsc70 and gp96. The quaternary, tertiary, and secondary structures of both proteins are evaluated by a variety of spectroscopic techniques, including far-UV circular dichroism, Trp fluorescence, ANS fluorescence, and derivative UV absorption spectroscopy. The results are summarized and compared employing an empirical phase diagram approach. Very similar behaviors are seen for both proteins despite their differences in sequence and tertiary structure. Both proteins show substantial conformational lability in responses to the pH and temperature changes of their environment. This study suggests a natural selection for related functional properties through common conformational dynamics rather than immediate structural homology.