heat shock proteins

Heat-shock proteins (otherwise known as HSPs or stress proteins) are molecular chaperones, present in all cells at all biological levels. They appear when the cell is under heat stress (or other environmental stress).

Heat-shock proteins also occur under non-stressful conditions, monitoring the cell's proteins. Some examples of their role as "monitors", or chaperones are the transport of old proteins to the cell's proteasomes. Further, HSPs correct folding of newly synthesized proteins. These activities are part of cell's self-monitoring and repair system, termed the 'cellular stress response' or the 'heat-shock response.' The function of heat-shock proteins is similar in virtually all living organisms, from bacteria to humans.

As molecular chaperones for other protein molecules, heat shock proteins are usually cytoplasmic proteins. They play an important role in protein-protein interactions such as folding and assisting in the establishment of proper protein conformation (shape), and the prevention of unwanted protein aggregation. By helping to stabilize partially unfolded proteins, HSPs aid in the transportation proteins across membranes within the cell. Some members of the HSP family are expressed at low to moderate levels in all organisms because of their essential role in protein maintenance. The HSPs are named according to their molecular weights, for example Hsp70 and Hsp90 each define families of chaperones.