Immune Response to Heat Shock Proteins

Abstract

Species as diverse as bacteria and humans respond quite uniformly to environmental assaults: their cells produce a well-defined and highly conserved group of proteins, termed stress proteins or heat shock proteins (HSP). These hsp can be grouped into different families according to their apparent molecular weight, e.g., the hsp 60 family which is in the focus of this small treatise has an apparent molecular mass of 60 kDa [1]. Members of this family are extremely conserved and the bacterial and human cognates share about 60% sequence homology [2]. Although hsp levels are normally increased under stress, many hsp already perform important functions in the normal cell (see Fig. 1). Hsp 60 have a high peptide-binding activity which allows them to interact with other proteins in the cell [1]. In eukaryotes, hsp 60 is primarily localized in mitochondria where it facilitates unfolding and folding steps of protein translocation from the cytoplasmic into the mitochondrial compartment as well as the assembly of high molecular weight complexes [3]. The hsp 60 cognate of Escherichia coli has been termed GroEL. Together with another hsp, GroES, it facilitates protein folding and unfolding, protein translocation across membrane barriers, and protein secretion. Hsp 60 is an abundant bacterial polypeptide which makes up 1% -2% of the total protein content under normal conditions and increases up to Fivefold in certain stress situations.