The role of Hot13p and redox chemistry in the mitochondrial TIM22 import pathway.
The small Tim proteins in the mitochondrial intermembrane space participate in the TIM22 import pathway for assembly of the inner membrane. Assembly of the small TIM complexes requires the conserved "twin CX3C" motif that forms juxtapositional intramolecular disulfide bonds. Here we identify a new intermembrane space protein, Hot13p, as the first component of a pathway that mediates assembly of the small TIM complexes. The small Tim proteins require Hot13p for assembly into a 70-kDa complex in the intermembrane space. Once assembled the small TIM complexes escort hydrophobic inner membrane proteins en route to the TIM22 complex. The mechanism by which the small Tim proteins bind and release substrate is not understood, and we investigated the affect of oxidant/reductant treatment on the TIM22 import pathway. With in organello import studies, oxidizing agents arrest the ADP/ATP carrier (AAC) bound to the Tim9p-Tim10p complex in the intermembrane space; this productive intermediate can be chased into the inner membrane upon subsequent treatment with reductant. Moreover, AAC import is markedly decreased by oxidant treatment in Deltahot13 mitochondria and improved when Hot13p is overexpressed, suggesting Hot13p may function to remodel the small TIM complexes during import. Together these results suggest that the small TIM complexes have a specialized assembly pathway in the intermembrane space and that the local redox state of the TIM complexes may mediate translocation of inner membrane proteins.
Curran
Sean P
SP
Department of Chemistry and Biochemistry, University of California, Los Angeles 90095-1569, USA.
Leuenberger
Danielle
D
Leverich
Edward P
EP
Hwang
David K
DK
Beverly
Kristen N
KN
Koehler
Carla M
CM
D000595:Amino Acid Sequence; D017124:Conserved Sequence; D017353:Gene Deletion; D007425:Intracellular Membranes / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism*; D000226:Mitochondrial ADP, ATP Translocases / Q000378:metabolism*; D033681:Mitochondrial Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D021381:Protein Transport; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*
D026901:Membrane Transport Proteins; D033681:Mitochondrial Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; D029701:Saccharomyces cerevisiae Proteins; C102549:TIM22 protein, S cerevisiae; D000226:Mitochondrial ADP, ATP Translocases