What is the function of the OXA complex in mitochondria?
Evolutionary conservation membrane insertases bacterial plasma membrane reveals OXA family YidC Alb3 Oxa1. Mitochondrial Oxa1 45 kDa inner membrane five transmembrane helices forms co-translational insertion site adjacent matrix mitoribosome large subunit near exit tunnel via Mrpl45 interaction. Several highly hydrophobic proteins encoded mitochondrial DNA including subunit II III cytochrome oxidase Cox2 Cox3 subunit a c ATP synthase Atp6 Atp9 cytochrome b Cob synthesized matrix mitoribosomes because extreme hydrophobicity would hamper import. Oxa1 central hydrophilic groove provides aqueous path lateral gate opening lipid bilayer facilitating insertion nascent helices using positive inside rule proton motive force independent ATP. Nuclear-encoded proteins first fully imported matrix via TIM23 such Cox18 dependent and some ATP synthase subunits also require subsequent export inner membrane conservative sorting analogous Sec-independent insertion again via Oxa1. Oxa1 does not insert beta-barrel outer proteins relying SAM complex Tob55 nor directly drive matrix import via TIM23 nor act proton pump; Complexes I III IV pump protons. Deletion Oxa1 yeast pleiotropic respiratory deficiency failure assembling Complexes IV V loss membrane potential and biogenesis.
Ref: Hennon et al., Front Physiol 2015: OXA insertase inserts proteins into mitochondrial inner membrane.