Tom40, the PoreForming Component of the Protein-Conducting Tom Channel in the Outer Membrane of Mitochondria

...Based on single-channel measurements (Ahting et al. 2001; Hill et al. 1998; Poynor et al. 2008; Romero-Ruiz et al. 2010) of isolated Tom40, an ion- and peptide-conducting pore in lipid membranes was demonstrated...
...Electron microscopy, electrophysiology and biochemical studies measuring the effect of rigid gold labels introduced into precursor proteins during import into mitochondria of S. cerevisiae indicated Tom40 pore diameters of *20 A ˚ (Hill et al. 1998; Kinoshita et al. 2007; Schwartz and Matouschek 1999; Suzuki et al. 2000; Werhahn et al. 2001, 2003; Ahting et al. 2001)...
...These results are in perfect agreement with former studies on fungal and mammalian Tom40 proteins, suggesting a bbarrel structure for Tom40 in all species (Becker et al. 2005; Hill et al. 1998; Kinoshita et al. 2007; Ahting et al. 2001; Suzuki et al. 2000) and an N-terminal a-helical segment adjacent to the b-barrel (Suzuki et al. 2004)...
...The channel conductance of hTom40ADN was in the same range as the recombinant yeast Tom40 measured at 250 mM KCl, with states at *210, *260, *440 and *430 pS (Harsman et al. 2010) as well as native Tom40 from N. crassa investigated in 1 M KCl with ?0.4, *0.8, *1.4, *2.0 and *2.9 nS (Ahting et al. 2001; Poynor et al. 2008; Romero-Ruiz et al. 2010)...

...This was very consistent with observations made previously under analogous conditions for OmpF (Basle ´ et al. 2004) and other Omps (Schiffler et al. 2007; Ruı´z et al. 2004; Harwardt et al. 2004; Marques et al. 2004; Rieß et al. 2003; Andersen et al. 2003; Ahting et al. 2001; Maier et al. 2001; De ` et al. 2000)...

...[16,17]. Similarly, single-particle analyses of the purified b-barrel subunit Sam50/Tob55 of the SAM (TOB) complex [2,57,58] reveals...

... TOM22 has been shown to be involved in protein translocation into mitochondria and has a dual role, as it is a component of the general insertion pore together with the pore-forming protein TOM40 and, as such, is involved in protein translocation across the mitochondrial outer membrane...

... analogous to a variety of other protein translocating channels, including the PapC outer membrane usher involved in the assembly of E. coli P pili, the Sec complex responsible for transport of proteins across the bacterial inner membrane and the eukaryotic endoplasmic reticulum, the TIM22 protein insertion complex in the mitochondrial inner membrane, and the TOM protein import complex in the mitochondrial outer membrane, among others (1, ...

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