Bacterial Expression, Purification and Characterization of a Rice Voltage-Dependent, Anion-Selective Channel Isoform, OsVDAC4

The voltage-dependent anion-selective channel (VDAC) is the most abundant protein in the mitochondrial outer membrane and forms the major conduit for metabolite transport across this membrane. VDACs from different sources show varied primary sequence but conserved functional properties. Here, we report on the characterization of a rice channel, OsVDAC4, which complements a VDAC1 deficiency in yeast. We present a consensus secondary structure prediction of an N-terminal alpha-helix and 19 beta-strands. Bacterially expressed OsVDAC4 was purified from inclusion bodies into detergent-containing solution, where it is largely helical. Detergent-solubilized OsVDAC4 inserts spontaneously into artificial membranes of two topologies-spherical liposomes and planar bilayers. Insertion into liposomes results in an increase in beta-structure. Transport of polyethylene glycols was used to estimate a pore diameter of similar to 2.6 nm in liposomes. Channels formed in planar bilayers exhibit large conductance (4.6 +/- A 0.3 nS in 1 M KCl), strong voltage dependence and weak anion selectivity. The open state of the channel is shown to be permeable to ATP. These data are consistent with a large beta-barrel pore formed by OsVDAC4 on inserting into membranes. This study forms a platform to carry out studies of the interaction of OsVDAC4 with putative modulators.