The effect of nucleotides and mitochondrial chaperonin 10 on the structureand chaperone activity of mitochondrial chaperonin 60

Mitochondrial chaperonins are necessary for the folding of newly imported a nd stress-denatured mitochondrial proteins. The goal of this study was to i nvestigate the structure and function of the mammalian mitochondrial chaper onin system. We present evidence that the 60 kDa chaperonin (mt-cpn60) exis ts in solution in dynamic equilibrium between monomers, heptameric single r ings and double-ringed tetradecamers. In the presence of ATP and the 10 kDa cochaperonin (mt-cpn10), the formation of a double ring is favored. ADP at very high concentrations does not inhibit malate dehydrogenase refolding o r ATP hydrolysis by mt-cpn60 in the presence of mt-cpn10. We propose that t he cis (mt-cpn60)(14).nuleotide.(mt-cpn10)(7) complex is not a stable speci es and does not bind ADP effectively at its trans binding site.