12 Functions of the hsp70 Protein Family: An Overview

Abstract

There has been speculation about the function of heat shock proteins ever since their discovery (Tissières et al. 1974). An early assumption was that they somehow serve to restore the status quo in cells that have experienced an acute and potentially damaging stress, and to protect against further injury. In 1980, Hightower noted that most inducers of the stress response lead to the accumulation of denatured or damaged proteins in cells and suggested that hsps somehow help to deal with this material. In recent years, these generalizations have been backed up by more specific studies of hsp function that have led to plausible molecular models for the mechanism of action of at least some of them. It has also become clear that hsps or closely related proteins are present in unstressed cells and perform functions essential for normal growth. In this chapter, I discuss the hsp70 family and argue that the role of these proteins (as well as that of some other hsps) is to promote the refolding and reassembly of proteins that have become denatured as a result of hyperthermia or other abuse. This role is an extension of one of the functions of the hsp70 family in unstressed cells, which is to aid the assembly of newly synthesized proteins.

I. LOCALIZATION OF HSP70 IN STRESSED CELLS
hsp70 is often the most prominent product of protein synthesis in stressed cells, and in heat-shocked Drosophila cells, most incorporation of [³⁵S]methionine is into this protein. It is thus easy to follow...