Intracellular Disposition of Mitochondrial Molecular Chaperones: Hsp60, mHsp70, Cpn10 and TRAP-1

Introduction This chapter reviews work on the intracellular disposition of a number of molecular chaperones that are generally believed to be localised and function mainly within the mitochondria of eukaryotic cells. However, in recent years, compelling evidence has accumulated from many lines of investigation indicating that several of these mitochondrial (m-) chaperones are also localised and perform important functions at a variety of other sites/compartments within cells (see [1, 2]). The four chaperone proteins that are the subjects of this chapter include the following: (i) the 60-kDa heat shock chaperonin protein (Hsp60, also known as chaperonin 60, Cpn60), which is a major protein in both stressed and unstressed cells and plays an essential role in the proper folding and assembly into oligomeric complexes of other proteins [3–6]; (ii) the 10-kDa heat shock chaperonin (Hsp10 or Cpn10), which is a co-chaperone for Hsp60 in the protein folding process [7]; (iii) the mitochondrial homologue of the major 70-kDa heat shock protein (mHsp70), which plays a central role in the import of various proteins into mitochondria and their proper folding [4, 6]; and (iv) the mitochondrial Hsp90 protein, which was originally identified in mammalian cells as the tumour necrosis factor receptor-associated protein-1 (TRAP-1) [8, 9] and is commonly referred to by this latter name. All of these proteins are encoded by nuclear genes, and, after translation of their transcripts in the cytosol, their protein products are then imported into mitochondria.