Mitochondrial localization and oligomeric structure of HClpP, the human homologue of E-coli ClpP

A bacterially expressed recombinant HClpP protein, the human homologue of E scherichia coli ClpP protease, was used to obtain specific polyclonal antib odies. Those antibodies identify a 26 kDa polypeptide in mitochondrial subc ellular fractions of rat and human liver. Immunofluorescence and electron m icroscopic studies demonstrate that the mammalian homologue of ClpP is loca ted in the mitochondrial matrix with a tendency to be found in association with the inner mitochondrial membrane. An HClpP recombinant protein with a truncated NH, terminus (missing the first 58 amino acid residues) shows a m olecular mass of 26 kDa under denaturing conditions. This N-truncated HClpP recombinant protein shows a native molecular mass of 340 kDa that is ident ical with the native molecular mass of the partially purified protein from rat liver mitochondria. Electron microscopy shows that the N-truncated reco mbinant HClpP has a ring shape with seven identical morphological units in the periphery, exhibiting a 7-fold symmetry. The native molecular mass and the electron microscopic studies suggest that mitochondrial ClpP is compose d of two heptameric rings with 7-fold symmetry, similar to E, coli ClpP. (C ) 1999 Academic Press.