Phosphatidylcholine affects the role of the sorting and assembly machinery in the biogenesis of mitochondrial ?-barrel proteins
18.09.2015
Schuler MH, Di Bartolomeo F, Böttinger L, Horvath SE, Wenz LS, Daum G, Becker T.
J Biol Chem. 2015;290(44):26523-32.
Two membrane-bound protein translocases mediate the import of beta-barrel proteins into the outer membrane of mitochondria. The TOM complex (translocase of the outer membrane) transport the precursor across the membrane and the SAM complex (sorting and assembly machinery) promotes its folding and insertion into the outer membrane. While the function of the protein translocases have been analyzed to some extend, the role of phospholipids is poorly understood. Recently, it was reported that the non-bilayer forming phosphatidylethanolamine and cardiolipin affect beta-barrel biogenesis by impairing already the transport across the TOM complex. We analyzed here the role of the most abundant phospholipid phosphatidylcholine, which is a bilayer-forming phospholipid. Surprisingly, depletion of phosphatidylcholine affects specifically the membrane insertion of beta-barrel proteins mediated by the SAM complex, but not the transport step via the TOM channel. Moreover, the biogenesis of alpha-helical TOM proteins, which are imported in a SAM-dependent manner, depends also on the presence of phosphatidylcholine. Thus, the function of the SAM complex requires phosphatidylcholine. We conclude that phospholipids differentially affect the activity of distinct protein translocases.
