Phosphatidylcholine affects the role of the sorting and assembly machinery in the biogenesis of mitochondrial ß-barrel proteins.

ABSTRACT

Two protein translocases drive the import of ß-barrel precursor proteins into the mitochondrial outer membrane The translocase of the outer membrane (TOM complex) promotes transport of the precursor to the intermembrane space, whereas the sorting and assembly machinery (SAM complex) mediates subsequent folding of the ß-barrel and its integration into the target membrane. The non-bilayer-forming phospholipids phosphatidylethanolamine (PE) and cardiolipin (CL) are required for the biogenesis of ß-barrel proteins. Whether bilayer-forming phospholipids such as phosphatidylcholine (PC), the most abundant phospholipid of the mitochondrial outer membrane, play a role in the import of ß-barrel precursors is unclear. In this study, we show that PC is required for stability and function of the SAM complex during the biogenesis of ß-barrel proteins. PC further promotes the SAM-dependent assembly of the TOM complex, indicating a general role of PC for the function of the SAM complex. In contrast to PE-deficient mitochondria precursor accumulation at the TOM complex is not affected by depletion of PC. We conclude that PC and PE affect the function of distinct protein translocases in mitochondrial ß-barrel biogenesis.