Mim1 functions in an oligomeric form to facilitate the integration of Tom20 into the mitochondrial outer membrane |
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Authors: | Popov-Celeketić Jelena Waizenegger Thomas Rapaport Doron |
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Affiliation: | 1 Institut für Physiologische Chemie der Universität München, 81377 Munich, Germany 2 Interfaculty Institute for Biochemistry, University of Tübingen, Hoppe-Seyler-Str. 4, 72076 Tübingen, Germany |
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Abstract: | The translocase of the outer mitochondrial membrane (TOM) complex is the general entry site into the organelle for newly synthesized proteins. Despite its central role in the biogenesis of mitochondria, the assembly process of this complex is not completely understood. Mim1 (mitochondrial import protein 1) is a mitochondrial outer membrane protein with an undefined role in the assembly of the TOM complex. The protein is composed of an N-terminal cytosolic domain, a central putative transmembrane segment (TMS) and a C-terminal domain facing the intermembrane space. Here we show that Mim1 is required for the integration of the import receptor Tom20 into the outer membrane. We further investigated what the structural characteristics allowing Mim1 to fulfil its function are. The N- and C-terminal domains of Mim1 are crucial neither for the function of the protein nor for its biogenesis. Thus, the TMS of Mim1 is the minimal functional domain of the protein. We show that Mim1 forms homo-oligomeric structures via its TMS, which contains two helix-dimerization GXXXG motifs. Mim1 with mutated GXXXG motifs did not form oligomeric structures and was inactive. With all these data taken together, we propose that the homo-oligomerization of Mim1 allows it to fulfil its function in promoting the integration of Tom20 into the mitochondrial outer membrane. |
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Keywords: | TOM, translocase of the outer mitochondrial membrane Mim1, mitochondrial import protein 1 TMS, transmembrane segment TOB, topogenesis of mitochondrial outer membrane β-barrel proteins IMS, intermembrane space BN, blue native WT, wild type DSG, disuccinimidyl glutarate NTA, nitrilotriacetic acid |
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