Role of Phosphatidylethanolamine in the Biogenesis of Mitochondrial Outer Membrane Proteins

Thomas Becker,Susanne E Horvath,Lena Böttinger,Natalia Gebert,Günther Daum,Nikolaus Pfanner

doi:10.1074/jbc.m112.442392

Thomas Becker, Susanne E Horvath + Show 4 more

Open Access

https://doi.org/10.1074/jbc.m112.442392

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Abstract

The mitochondrial outer membrane contains proteinaceous machineries for the import and assembly of proteins, including TOM (translocase of the outer membrane) and SAM (sorting and assembly machinery). It has been shown that the dimeric phospholipid cardiolipin is required for the stability of TOM and SAM complexes and thus for the efficient import and assembly of β-barrel proteins and some α-helical proteins of the outer membrane. Here, we report that mitochondria deficient in phosphatidylethanolamine (PE), the second non-bilayer-forming phospholipid, are impaired in the biogenesis of β-barrel proteins, but not of α-helical outer membrane proteins. The stability of TOM and SAM complexes is not disturbed by the lack of PE. By dissecting the import steps of β-barrel proteins, we show that an early import stage involving translocation through the TOM complex is affected. In PE-depleted mitochondria, the TOM complex binds precursor proteins with reduced efficiency. We conclude that PE is required for the proper function of the TOM complex.

Highlights

It is unknown if phosphatidylethanolamine (PE), the major non-bilayer-forming mitochondrial phospholipid, is involved in the biogenesis of outer membrane proteins
Biogenesis of ␤-Barrel Proteins Is Impaired in PE-deficient Mitochondria—To study the role of PE in the biogenesis of mitochondrial outer membrane proteins, we isolated mitochondria from the psd1⌬ yeast strain and the psd1⌬ psd2⌬ double deletion strain (47, 73, 76)
We have demonstrated that PE is required for the full activity of the main protein entry gate of mitochondria

Summary

Background

It is unknown if phosphatidylethanolamine (PE), the major non-bilayer-forming mitochondrial phospholipid, is involved in the biogenesis of outer membrane proteins. It has been shown that the dimeric phospholipid cardiolipin is required for the stability of TOM and SAM complexes and for the efficient import and assembly of ␤-barrel proteins and some ␣-helical proteins of the outer membrane. We report that mitochondria deficient in phosphatidylethanolamine (PE), the second non-bilayer-forming phospholipid, are impaired in the biogenesis of ␤-barrel proteins, but not of ␣-helical outer membrane proteins. A specialized SAM form containing Mdm[10] (mitochondrial distribution and morphology protein 10) mediates the biogenesis of Tom[22], whereas other single-spanning precursor proteins insert independently of known proteinaceous factors but can be impaired by elevated levels of ergosterol (31–38). The outer membrane contains only small amounts of CL, lack of CL causes destabilization of TOM and SAM complexes and reduced precursor binding by the translocases. We conclude that PE is required for the efficient function of the TOM machinery

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION