Oligomeric states of the voltage-dependent anion channel and cytochrome c release from mitochondria

Abstract

The VDAC (voltage-dependent anion channel) plays a central role in apoptosis, participating in the release of apoptogenic factors including cytochrome c. The mechanisms by which VDAC forms a protein-conducting channel for the passage of cytochrome c are not clear. The present study approaches this problem by addressing the oligomeric status of VDAC and its role in the induction of the permeability transition pore and cytochrome c release. Chemical cross-linking of isolated mitochondria or purified VDAC with five different reagents proved that VDAC exists as dimers, trimers or tetramers. Fluorescence resonance energy transfer between fluorescently labelled VDACs supports the concept of dynamic VDAC oligomerization. Mitochondrial cross-linking prevented both permeability transition pore opening and release of cytochrome c, yet had no effect on electron transport or Ca 2+ uptake. Bilayer-reconstituted purified cross-linked VDAC showed decreased conductance and voltage-independent channel activity. In the dithiobis(succinimidyl propionate)-cross-linked VDAC, these channel properties could be reverted to those of the native VDAC by cleavage of the cross-linking. Cross-linking of VDAC reconstituted into liposomes inhibited the release of the proteoliposome-encapsulated cytochrome c. Moreover, encapsulated, but not soluble cytochrome c induced oligomerization of liposome-reconstituted VDAC. Thus the results indicate that VDAC exists in a dynamic equilibrium between dimers and tetramers and suggest that oligomeric VDAC may be involved in mitochondriamediated apoptosis.

Structure of the human voltage-dependent anion channel

“…Previous studies have indicated that VDAC from several species can exist in different oligomerization states from monomers to dimers, trimers, tetramers, hexamers, and higher oligomers (27)(28)(29). A transient dimerization is in agreement with chemical crosslinking experiments where dimers and higher-order oligomers were found in diluted solutions of hVDAC1.…”

The voltage-dependent anion channel-1 modulates apoptotic cell death

“…VDAC, a major mitochondrial outer membrane transporter, plays an important role in apoptosis by participating in the release of intermembrane space proteins including cytochrome c. 3,4,6,[8][9][10][33][34][35] Investigating the role of VDAC in cellular processes is, however, limited by a lack of tools such Figure 3 RuR inhibits channel activity of native but not E72Q-mutated mVDAC1. Purified native or E72Q-mVDAC1 was reconstituted into a PLB.…”

“…Nevertheless, it seems that the closed/open configuration of VDAC with respect to transport of ions and metabolites is not directly applied to movement of intermembranal space proteins such as cytochrome c. A distinct VDACassociated pathway, an internal VDAC pore for movement of small molecules and a large channel formed by VDAC monomers for cytochrome c release have recently been suggested. 35 …”

“…35 As such, VDAC overexpression, which leads to increase in its concentration, would encourage VDAC oligomerization, and thus allow for release of proapoptotic proteins (such as cytochrome c) from the mitochondrial intermembrane space. Support for involvement of VDAC oligomerization in apoptosis is presented in recent studies on the reagent As 2 O 3 , where its apoptosis-inducing effect was attributed to an induction of homodimerization of VDAC molecules.…”

Proapoptotic multidomain Bcl-2/Bax-family proteins: mechanisms, physiological roles, and therapeutic opportunities

“…95,96 Interestingly, VDAC1 has been reported to bind Bax, but the significance of this interaction is controversial. [97][98][99][100] Altogether, the available data indicate that while MDPs may be interchangeable in terms of many or most of their effector functions, the upstream afferent inputs into these proteins vary considerably thus giving each MDP its unique biology (Figure 3). …”