Modulation of the Channel Activity of the C-Subunit of the ATP Synthase by Polyphosphate and Polyhydroxybutyrate

Abstract

C subunit of the ATP synthase has been proposed to be the main constituent of the channel part of the mitochondrial Permeability Transition Pore (mPTP) complex. Our earlier work demonstrated that when c subunit is co-purified from mitochondria together with polyphosphate (polyP) and polyhydroxybutyrate (PHB), it forms channels resembling native mPTP. Our work is aimed at better understanding the interactions among these three macromolecules and their role in the formation of the pore. We extracted c subunit from rat liver mitochondria in physiological conditions and from mitochondria after the induction of permeability transition by a method that excludes formation of complex with polyP. This was followed by the study of ion channel activity in planar lipid membranes and its modulation by the addition of synthetic polyP and PHB. We observed channel activity in all preparations. Moreover, the presence of polyP together with Ca2+ led to the increase in channel conductance from ∼600 pS up to ∼1.7 nS. Circular dichroism spectroscopy indicated that, unlike native c subunit being primarily in an α-helical conformation, under our reconstitution conditions c subunit possessed a significant amount of β-sheet. We hypothesize that channel activity of the c subunit might be related to its misfolding under pathological conditions and that this process can be modulated by polyP and PHB.