Grp75, also known as mortalin, is a member of Hsp70 family of chaperone proteins that is not heat inducible (1, 2). Grp75 is actually induced under conditions of low glucose and other nutritional and environmental stresses. Grp75 resides primarily in the mitochondrial matrix, where it collaborates with Hsp60 in the re-folding of proteins translocated into this organelle (3, 4). Related forms may also be found in the cytosol or on the surface of the extracellular membrane.
Other Grp75 functions include its ability to inactivate the tumor suppressor p53 (5). Studies have found that Grp75 is over-expressed in many tumor tissues and immortalized human cell lines, suggesting its role in the tumor formation (6). Grp75 is also implicated in cell aging, as its overexpression appears to prolong the life span of human fibroblasts (7). And finally, like its E.coli homolog DnaK (8), GRP75 possesses a cation-dependent ATPase activity considered central to its function as a chaperone (9, 10).