Biological and Biochemical Basis of Thermotolerance

Abstract

When living cells are exposed to non-lethal heat shock, they acquire a transient resistance to a subsequent heat challenge as determined by the increase in cell survival. This phenomenon is termed thermotolerance. In addition, it has recently been demonstrated that non-lethal mild heat shock induced a transient thermotolerant state of cellular structures and functions such as protein and RNA synthesis, RNA splicing, cytoskeletons and cell morphology. On the other hand, a brief heat shock and other environmental stresses are known to induce a family of proteins, called heat shock or stress proteins (hsps). There is much evidence to support the correlation between the development of thermotolerance and the enhanced synthesis of heat shock proteins, but some reports do not concur. Recently, some hsps (especially hsp70) has been shown to have a molecular chaperoning activity involved in folding and unfolding of proteins and assembly and disassembly of protein complexes under normal growth temperature. Also, hsp70 and DnaK protein (prokaryotic homologue of eukaryotic hsp70) have been suggested to associate with heat- or stress-denatured (unfolded) proteins and repair (fold) them using the energy of ATP.
In this review, we attempted to interprete the phenomenon of thermotolerance based on the putative functions of hsps (especially hsp70) which have a molecular chaperoning activity and a protein repair enzyme activity.