Purification and Characterization of the Voltage-Dependent Anion-Selective Channel Protein from Wheat Mitochondrial Membranes

An approximately 29-kD protein was purified from the membrane fraction of wheat (Triticum aestivum cv Dganit) mitochondria by the utilization of standard liquid chromatography techniques. The protein, designated MmP29 for mitochondrial membrane protein having a molecular mass of approximately 29 kD, exhibited cationic properties in a buffering solution, adjusted to pH 7.5. This positive charge enabled its passage through a diethylaminoethyl column, without interaction with the positively charged matrix. Subsequently, this protein was separated from the remaining polypeptides by a preferential elution from a hydroxylapatite/celite mixed column. Reconstituted liposomes containing this protein were characterized as being permeable to 8-amino-naphthalene 1,3,6-trisulfonic acid disodium salt (Mr 445) but non-permeable to dextran fluorescein (Mr 40,000). Additionally, MmP29 was inserted into planar phospholipid membranes, and anion-selective, voltage-dependent channels were demonstrated. All of the MmP29 properties mentioned highly resemble voltagedependent, anion-selective channel (VDAC) proteins, suggesting that MmP29 is the mitochondrial outer membrane VDAC protein of wheat.