title: Molecular chaperone Hsp70/Hsp90 prepares the mitochondrial outer membrane translocon receptor Tom71 for preprotein loading.
abstract: The preproteins targeted to the mitochondria are transported through the translocase of the outer membrane complex. Tom70/Tom71 is a major surface receptor of the translocase of the outer membrane complex for mitochondrial preproteins. The preproteins are escorted to Tom70/Tom71 by molecular chaperones Hsp70 and Hsp90. Here we present the high resolution crystal structures of Tom71 and the protein complexes between Tom71 and the Hsp70/Hsp90 C terminus. The crystal structures indicate that Tom70/Tom71 may exhibit two distinct states. In the closed state, the N-terminal domain of Tom70/Tom71 partially blocks the preprotein-binding pocket. In the open state, the N-terminal domain moves away, and the preprotein-binding pocket is fully exposed. The complex formation between the C-terminal EEVD motif of Hsp70/Hsp90 and Tom71 could lock Tom71 in the open state where the preprotein-binding pocket of Tom71 is ready to receive preproteins. The interactions between Hsp70/Hsp90 and Tom71 N-terminal domain generate conformational changes that may increase the volume of the preprotein-binding pocket. The complex formation of Hsp70/Hsp90 and Tom71 also generates significant domain rearrangement within Tom71, which may position the preprotein-binding pocket closer to Hsp70/Hsp90 to facilitate the preprotein transfer from the molecular chaperone to Tom71. Therefore, molecular chaperone Hsp70/Hsp90 may function to prepare the mitochondrial outer membrane receptor Tom71 for preprotein loading.
authors: Department of Cell Biology, University of Alabama at Birmingham, Birmingham, Alabama 35294-0005, USA.
authors: Jingzhi
authors: J
authors: Li
authors: Xinguo
authors: X
authors: Qian
authors: Junbin
authors: J
authors: Hu
authors: Bingdong
authors: B
authors: Sha
mesh_terms: D000595:Amino Acid Sequence; D018840:HSP70 Heat-Shock Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018841:HSP90 Heat-Shock Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D033681:Mitochondrial Membrane Transport Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary; D012441:Saccharomyces cerevisiae / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment
chemical_list: D018840:HSP70 Heat-Shock Proteins; C074510:HSP82 protein, S cerevisiae; D018841:HSP90 Heat-Shock Proteins; D033681:Mitochondrial Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; C090869:SSA3 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C489039:TOM70 protein, S cerevisiae; C099144:TOM71 protein, S cerevisiae