Persistence of the mitochondrial permeability transition in the absence of subunit c of human ATP synthase

Abstract

The permeability transition in human mitochondria refers to the opening of a nonspecific channel, known as the permeability transition pore (PTP), in the inner membrane. Opening can be triggered by calcium ions, leading to swelling of the organelle, disruption of the inner membrane, and ATP synthesis, followed by cell death. Recent proposals suggest that the pore is associated with the ATP synthase complex and specifically with the ring of c-subunits that constitute the membrane domain of the enzyme's rotor. The c-subunit is produced from three nuclear genes, ATP5G1, ATP5G2, and ATP5G3, encoding identical copies of the mature protein with different mitochondrial-targeting sequences that are removed during their import into the organelle. To investigate the involvement of the c-subunit in the PTP, we generated a clonal cell, HAP1-A12, from near-haploid human cells, in which ATP5G1, ATP5G2, and ATP5G3 were disrupted. The HAP1-A12 cells are incapable of producing the c-subunit, but they preserve the characteristic properties of the PTP. Therefore, the c-subunit does not provide the PTP. The mitochondria in HAP1-A12 cells assemble a vestigial ATP synthase, with intact F 1 -catalytic and peripheral stalk domains and the supernumerary subunits e, f, and g, but lacking membrane subunits ATP6 and ATP8. The same vestigial complex plus associated c-subunits was characterized from human 143B ρ 0 cells, which cannot make the subunits ATP6 and ATP8, but retain the PTP. Therefore, none of the membrane subunits of the ATP synthase that are involved directly in transmembrane proton translocation is involved in forming the PTP.human mitochondria | ATP synthase | permeability transition pore | subunit c | ATP5G

Permeability transition in human mitochondria persists in the absence of peripheral stalk subunits of ATP synthase

“…Pore Opening in HAP1-Δb and HAP1-ΔOSCP Cells. Under the optimum conditions established previously (24), PTP opening in intact HAP1-WT cells was demonstrated in the presence of both thapsigargin and the calcium ionophore ferutinin, and was prevented by the addition of CsA. Similar results were obtained with HAP1-Δb and HAP1-ΔOSCP cells (Fig.…”

“…6). Previously, this mitochondrial import precursor protein has been observed intact in association with another related but distinct vestigial ATPase complex inside the mitochondria derived from human ρ 0 cells (24,37). Whether IF 1 -P follows the same pathway of entry into the mitochondria of these cells as IF 1 -M1, or whether indeed IF 1 -P is capable of inhibiting ATP hydrolysis, is unknown.…”

“…One specific proposal, that the PTP is provided by a ring of eight c subunits in the membrane sector of the enzyme's rotor (22,23), has been disproved in a clonal cell line in which the three genes encoding subunit c have been disrupted (24). Although these cells are incapable of making subunit c, the characteristic properties of the PTP persist (24). Another idea, that two other membrane components of the ATP synthase, subunits a (or ATP6) and A6L (or ATP8), might participate in PTP formation has been disproved as well.…”

“…Another idea, that two other membrane components of the ATP synthase, subunits a (or ATP6) and A6L (or ATP8), might participate in PTP formation has been disproved as well. In human ρ o cells, which lack the mitochondrial genome and thus are devoid of both subunits, the PTP persists (24,25).…”

Structure and function of the intermembrane space domain of mammalian FoF1ATP synthase

“…Accordingly, the mammalian IMD might be involved in gating of the mitochondrial permeability pore by controlling the lipid plug [38] or the dimer interface. A function of the rotor-ring lumen as the pore is currently a matter of debate [39,40].…”