Electrophysiological Characterization of two Novel Ion Channels of Mitochondria

Abstract

Mitochondrial ion channels are of great importance to ensure the proper function of this bioenergetic organelle and to regulate cell fate. However, in many cases our knowledge concerning their molecular identity and regulation is still limited. Here we describe a novel regulatory mechanism of the voltage-dependent anion channel VDAC3 and a new channel-forming protein. Voltage-dependent anion channels (VDAC), also known as eukaryotic porins, are located in the outer mitochondrial membrane and allow the flux of ions and small metabolites. While the pore-forming ability of recombinant VDAC1 and VDAC2 has been extensively studied during the last decades, a clear-cut ion conducting channel activity has been assigned to the VDAC3 isoform only recently (Checchetto et al, Cell Phys Biochem, 2014). This protein forms an ion channel with small conductance under standard conditions, but our study identifies the amino acid residues whose oxidation state impacts on channel activity and conductance. Furthermore, we characterize from electrophysiological point of view a novel protein complex composed by pore-forming core and regulatory subunits located in the inner mitochondrial membrane. Channel activity can be observed with the reconstituted recombinant core protein, but for its regulation the co-expression of both the core and the regulatory subunits are necessary. Overall, our data suggest that VDAC3 and the novel protein complex are new players in the control of mitochondrial ion homeostasis and might contribute to the plasticity of mitochondrial function in intact cells.