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An essential novel component of the noncanonical mitochondrial outer membrane protein import system of trypanosomatids
Authors:Mascha Pusnik  Jan Mani  Oliver Schmidt  Moritz Niemann  Silke Oeljeklaus  Felix Schnarwiler  Bettina Warscheid  Trevor Lithgow  Chris Meisinger  André Schneider
Institution:Department of Chemistry and Biochemistry, University of Bern, CH-3012 Bern, Switzerland Institute for Biochemistry and Molecular Biology, Centre for Biochemistry and Molecular Cell Research BIOSS Centre for Biological Signalling Studies, University of Freiburg, 79104 Freiburg, Germany Faculty of Biology, University of Freiburg, 79104 Freiburg, Germany Department of Biochemistry and Molecular Biology, Monash University, Clayton 3800, Australia.
Abstract:The mitochondrial outer membrane protein Tom40 is the general entry gate for imported proteins in essentially all eukaryotes. Trypanosomatids lack Tom40, however, and use instead a protein termed the archaic translocase of the outer mitochondrial membrane (ATOM). Here we report the discovery of pATOM36, a novel essential component of the trypanosomal outer membrane protein import system that interacts with ATOM. pATOM36 is not related to known Tom proteins from other organisms and mediates the import of matrix proteins. However, there is a group of precursor proteins whose import is independent of pATOM36. Domain-swapping experiments indicate that the N-terminal presequence-containing domain of the substrate proteins at least in part determines the dependence on pATOM36. Secondary structure profiling suggests that pATOM36 is composed largely of α-helices and its assembly into the outer membrane is independent of the sorting and assembly machinery complex. Taken together, these results show that pATOM36 is a novel component associated with the ATOM complex that promotes the import of a subpopulation of proteins into the mitochondrial matrix.
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