PROSITE documentation PDOC00269

Heat shock hsp70 proteins family signatures

Prokaryotic and eukaryotic organisms respond to heat shock or other environmental stress by the induction of the synthesis of proteins collectively known as heat-shock proteins (hsp) [1]. Amongst them is a family of proteins with an average molecular weight of 70 Kd, known as the hsp70 proteins [2,3,4]. In most species, there are many proteins that belong to the hsp70 family. Some of them are expressed under unstressed conditions. Hsp70 proteins can be found in different cellular compartments (nuclear, cytosolic, mitochondrial, endoplasmic reticulum, etc.). Some of the hsp70 family proteins are listed below:

• In Escherichia coli and other bacteria, the main hsp70 protein is known as the dnaK protein. A second protein, hscA, has been recently discovered. dnaK is also found in the chloroplast genome of red algae.
• In yeast, at least ten hsp70 proteins are known to exist: SSA1 to SSA4, SSB1, SSB2, SSC1, SSD1 (KAR2), SSE1 (MSI3) and SSE2.
• In Drosophila, there are at least eight different hsp70 proteins: HSP70, HSP68, and HSC-1 to HSC-6.
• In mammals, there are at least eight different proteins: HSPA1 to HSPA6, HSC70, and GRP78 (also known as the immunoglobulin heavy chain binding protein (BiP)).
• In the sugar beet yellow virus (SBYV), a hsp70 homolog has been shown [5] to exist.
• In archaebacteria, hsp70 proteins are also present [6].

All proteins belonging to the hsp70 family bind ATP. A variety of functions has been postulated for hsp70 proteins. It now appears [7] that some hsp70 proteins play an important role in the transport of proteins across membranes. They also seem to be involved in protein folding and in the assembly/ disassembly of protein complexes [8].

We have derived three signature patterns for the hsp70 family of proteins; the first centered on a conserved pentapeptide found in the N-terminal section of these proteins; the two others on conserved regions located in the central part of the sequence.