Plant VDAC Permeability: Molecular Basis and Role in Oxidative Stress

Abstract

The mitochondrial voltage-dependent anion-selective channel (VDAC) is highly abundant in the mitochondrial outer membrane. It is permeable to molecules with a size up to about 5kDa and is the main pathway for the exchange of metabolites and ions between the mitochondrial intermembrane space and the cytosol. Experimental studies performed for plant VDAC have shown that the channel displays properties reported for VDACs of other eukaryotic organisms. Firstly, it transports compounds as diverse as inorganic ions (e.g., K + and Cl -), adenylates (e.g., ATP and AMP) and large macromolecules (tRNA and DNA). Secondly, despite its wide pore, the channel displays selectivity towards these compounds, i.e. it distinguishes between K + and Clbut also between ATP and AMP. The question of how VDAC can selectively transport these different compounds is addressed in this chapter based on data obtained for plant VDAC. It is well known that all organisms have at least one canonical VDAC isoform that shares similar electrophysiological properties and secondary structure with cognate VDAC of other organisms. For instance, this is the case of the mammalian VDAC1, the yeast Saccharomyces cerevisiae VDAC1 and the PcVDAC purified from the bean Phaseolus coccineus seeds. Consequently, Brownian dynamic simulations of monatomic ion permeation through the experimental threedimensional structure of the mammalian VDAC1 and the PcVDAC modeled structure predict fairly well conductance and selectivity of both the proteins. In addition, the data of molecular simulation studies performed on the mammalian VDAC1 agree with the experimental data obtained for PcVDAC, which suggests a similar permeation process for these VDAC proteins. Accordingly, both the experimental and theoretical studies indicate that the selectivity for inorganic ions is a consequence of the excess of positive charges and their distribution inside the pore and the absence of defined pathways for the permeation. In contrast, the permeation of metabolites involves a major binding site located at the N-terminal helix which folded into the pore lumen and occurs through a preferential pathway. The key residues forming the binding site are conserved in the PcVDAC pointing to the conserved permeation process. The process might be affected by VDAC-interaction with other proteins. For example, it is suggested that plant VDAC is involved in the oxidative stress response which includes cytosolic hexokinase and thioredoxin binding to VDAC. This in turn may influence the exchange of molecules between mitochondria and the cytosol.

Stripe Rust Effector Pst_9302 Inhibits Wheat Immunity to Promote Susceptibility

“…VDACs regulate the transport of substances between cytoplasm and mitochondria, e.g., K + , Cl − , Ca 2+ , HPO 4 2− , ATP 4− , O 2− , and mitochondria-mediated cell death [46]. In plants, studies have shown that VDACs not only affect plant development but also positively regulate pathogen defense [48]. Arabidopsis AtVDAC1 regulates infection resistance to Agrobacterium tumefaciens.…”

“…qRT-PCR analyses showed that the expression level of Pst_9302 was reduced by 60-75% in Pst_9302 knockdown plants compared to in the control plants (Figure 6B). Histological observation revealed that the hyphal branch per infection site was significantly reduced in Pst_9302-silencing wheat plants at 48 hpi compared to that in the control leaves (Figure 7A-C). At both 48 hpi and 120 hpi, the Pst infection areas were significantly decreased in Pst_9302-silencing wheat plants compared to those in the control leaves (Figure 7D,E).…”