(10) A COMPARISON OF THE ACTIVITIES OF MCC AND PSC, THE PROTEIN TRANSLOCATING CHANNELS OF MITOCHONDRIA

M.L. Campo (1), C. Muro (1), A. Gazquez (1) and K.W. Kinnally (2)
(1) Dpto. de Bioquimica, Univ. de Extremadura, Spain
(2) Division of Molecular Medicine, Wadsworth Center, Empire State Plaza, Albany, NY and Department of Biomedical Sciences, University at Albany, Albany, NY

About 95% of all mitochondrial proteins are encoded in the nucleus and synthesized in the cytosol. These precursor proteins are imported into mitochondria by import complexes called Tim and Tom in the inner and outer membranes, respectively. MCC and PSC are the water-filled channels that putatively function in protein translocation in these Timand Tom complexes.

We have conducted a comparative study of the single channel characteristics of MCC and PSC from S. cerevisiae mitochondria reconstituted in proteoliposomes using patch-clamp techniques. We determined the functional effects on MCC and PSC behavior of structurally modifying the Tim and Tom complexes by deleting or proteolytically cleaving components. Tim23p and Tom22p are thought to be the receptors of the Tim and Tom complexes, respectively, that recognize the mitochondrial targeting region of precursor proteins. Importantly, intact Tim23p and Tom22p were requisite for regulation of MCC and PSC by targeting peptides. Loss of Tom70p and Tom20p had no effect on PSC or MCC. These data are consistent with the idea that MCC and PSC are distinct entities whose activities are regulated by presequence peptides and by modifications to the Tim and Tom complexes, respectively, and that MCC and PSC are the protein translocation channels of mitochondria.

This work was supported by DGICYT grant PB95-0456 and Junta de Extremadura y Fondo Social Europeo grant EIA94-11 to MLC and NSF grant MCB9513439 to KWK.