Signal presequences increase mitochondrial permeability and open the multiple conductance channel

We have reported that the signal presequence of cytochrome oxidase subunit IV from Neurospora crassa increases the permeability of isolated rat liver mitochondria [P. M. Sokolove and K. W. Kinnally (1996) Arch. Biochem. Bioph ys, 336, 69] and regulates the behavior of the mutiple conductance channel (MCC) of yeast inner mitochondrial membrane [T. A. Lohret and K. W. Kinnall y (1995) J. Biol. Chem, 270, 15950], Here we examine in greater detail the action of a number of mitochondrial presequences from various sources and o f several control peptides on the permeability of isolated rat liver mitoch ondria and on MCC activity monitored via patch-clamp techniques in both mam malian mitoplasts and a reconstituted yeast system. The data indicate that the ability to alter mitochondrial permeability is a property of most, but not all, signal peptides, Furthermore, it is clear that, although signal pe ptides are characterized by positive charge and the ability to form amphiph ilic cu helices, these two characteristics are not sufficient to guarantee mitochondrial effects, Finally, the results reveal a strong correlation bet ween peptide effects on the permeability of isolated mitochondria and on MC C activity: peptides that induced swelling of mouse and rat mitochondria al so activated the quiescent MCC of mouse mitoplasts and induced flickering o f active MCC reconstituted from yeast mitochondrial membranes. Moreover, re lative peptide efficacies were very similar for mitochondrial swelling and both types of patch-clamp experiments. We propose that patch-clamp recordin gs of MCC activity and the high-amplitude swelling induced by signal peptid es reflect the opening of a single channel. Based on the selective responsi veness of that channel to signal peptides and the dependence of its opening in isolated mitochondria on membrane potential, we further suggest that th e channel is involved in the mitochondrial protein import process. (C) 1999 Acaaemic Press.