The voltage-dependent anion channel, a major component of the tRNA import machinery in plant mitochondria

Abstract

In plants, as in most eukaryotic cells, import of nuclear-encoded cytosolic tRNAs is an essential process for mitochondrial biogenesis. Despite its broad occurrence, the mechanisms governing RNA transport into mitochondria are far less understood than protein import. This article demonstrates by Northwestern and gel-shift experiments that the plant mitochondrial voltage-dependent anion channel (VDAC) protein interacts with tRNA in vitro. It shows also that this porin, known to play a key role in metabolite transport, is a major component of the channel involved in the tRNA translocation step through the plant mitochondrial outer membrane, as supported by inhibition of tRNA import into isolated mitochondria by VDAC antibodies and Ruthenium red. However VDAC is not a tRNA receptor on the outer membrane. Rather, two major components from the TOM (translocase of the outer mitochondrial membrane) complex, namely TOM20 and TOM40, are important for tRNA binding at the surface of mitochondria, suggesting that they are also involved in tRNA import. Finally, we show that proteins and tRNAs are translocated into plant mitochondria by different pathways. Together, these findings identify unexpected components of the tRNA import machinery and suggest that the plant tRNA import pathway has evolved by recruiting multifunctional proteins. mitochondrial porin ͉ cytosolic tRNAs ͉ import factor

Mitochondrial tRNA import in Trypanosoma brucei is independent of thiolation and the Rieske protein

“…In terms of the involvement of protein factors in tRNA import, the VDAC is important in plants (Salinas et al 2006), but establishing its specific role will require further exploration. In light of our knowledge of the tRNA Lys import in yeast, the placement of the RIC among the inner mitochondrial membrane proteins in L. tropica is not unprecedented (Mukherjee et al 2007).…”

“…In plants, for instance, the voltagedependent anion channel (VDAC) in the outer membrane was shown to play a crucial role for import in vitro (Salinas et al 2006). However, the homologous protein is dispensable for import in T. brucei (Pusnik et al 2009).…”

Plant-Specific Preprotein and Amino Acid Transporter Proteins Are Required for tRNA Import into Mitochondria

“…In yeast (Saccharomyces cerevisiae), the cytosolic tRNA for Lys is bound specifically by glycolytic enolase and transferred to the precursor of the mitochondrial lysyl-tRNA synthetase at the mitochondrial surface, after which it is cotransported through the protein import apparatus (Tarassov et al, 1995;Sepuri et al, 2012). In plants, the VDAC and components of the protein import apparatus such as Tom20 and Tom40 have been shown to be involved in tRNA import (Salinas et al, 2006). Furthermore, the addition of nucleic acid-binding proteins improves tRNA import rates in vitro, suggesting the involvement of as yet unidentified cytosolic factors.…”

“…Subsequently, an in vitro tRNA uptake assay was established, which showed the uptake of cytosolic tRNA into isolated mitochondria (Sieber et al, 2011). Further studies have suggested that there is cooperation among components of the protein import translocase of the outer membrane (TOM) and Porin/voltage-dependent anion channel (VDAC), although specific proteins dedicated for the import of tRNA have yet to be identified (Salinas et al, 2006).…”

Approaching the structure of human VDAC1, a key molecule in mitochondrial cross-talk

“…Recently, the attachment of the lipid synthesis protein STAR to VDAC during the life cycle of a eukaryotic cell was described (Bose et al 2008). Other reports depict VDAC as part of a tRNA uptake system in plant cells (Salinas et al 2006). …”