Role of the small protein Mco6 in the mitochondrial sorting and assembly machinery

Abstract

The majority of mitochondrial precursor proteins are imported through the Tom40 beta-barrel channel of the translocase of the outer membrane (TOM). The sorting and assembly machinery (SAM) is essential for beta-barrel membrane protein insertion into the outer membrane and thus required for the assembly of the TOM complex. Here we demonstrate that the alpha-helical outer membrane protein Mco6 forms a complex with the mitochondrial distribution and morphology protein Mdm10 as part of the SAM machinery. Moreover, Mco6 also interacts with the subunit Mim1 of the mitochondrial import complex (MIM), which is itself required for the biogenesis of alpha-helical outer membrane proteins. MCO6 and MDM10 display a negative genetic interaction and a MCO6-MDM10 yeast double mutant contains reduced levels of TOM complex. Cells lacking Mco6 affect the levels of Mdm10 and MIM-subunits associated with assembly defects of the TOM complex. Thus, this work reveals a role of the SAM-Mco6 complex for the biogenesis of the mitochondrial outer membrane.