Tom40, the import channel of the mitochondrial outer membrane, plays an active role in sorting imported proteins.
The Translocase of the Outer Mitochondrial membrane (TOM complex) is centred on a channel, created by Tom40, serving as the only means of entry for proteins into the mitochondrion. Proteins destined for internal mitochondrial compartments interact subsequently with one of the two distinct protein Translocases of the Inner Mitochondrial membrane (TIM23 and TIM54 complexes) or follow specialized paths into the intermembrane space. To investigate the sorting of precursor proteins to these various sub-mitochondrial compartments, we created a library of tom40 mutants and screened for alleles selectively corrupt in protein sorting. One of the tom40 mutants, tom40-97, carries a single point mutation (W(243)R) resulting in an ineffective transfer of precursors to the TIM23 complex. There is no defect on transfer of precursors to the TIM54 complex or insertion of proteins into the outer membrane. The Tom40 channel is not a passive pore, but plays an active role in protein sorting for all sub-mitochondrial locations.
Russell Grimwade School of Biochemistry and Molecular Biology, University of Melbourne, Parkville 3010, Australia.
Kipros
K
Gabriel
Billie
B
Egan
Trevor
T
Lithgow
D000595:Amino Acid Sequence; D006801:Humans; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism*; D033681:Mitochondrial Membrane Transport Proteins; D024101:Mitochondrial Proteins / Q000378:metabolism; D008969:Molecular Sequence Data; D017354:Point Mutation; D021381:Protein Transport / Q000502:physiology*; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000502:physiology; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment
D026901:Membrane Transport Proteins; D033681:Mitochondrial Membrane Transport Proteins; D024101:Mitochondrial Proteins; D029701:Saccharomyces cerevisiae Proteins; C066555:Tom40 protein, S cerevisiae