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© The Rockefeller University Press, 0021-9525/1999//959 $5.00
The Journal of Cell Biology, Volume 147, Number 5, , 1999 959-968

Original Article

The Tom Core Complex

: The General Protein Import Pore of the Outer Membrane of Mitochondria



Uwe Ahtinga, Clemens Thuna, Reiner Hegerlb, Dieter Typkeb, Frank E. Nargangc, Walter Neuperta, and Stephan Nussbergera

a Institut für Physiologische Chemie der Universität München, D-80336 München, Germany
b Abteilung für Molekulare Strukturbiologie, Max-Planck Institut für Biochemie, D-82152 Martinsried, Germany
c Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada
Institut für Physiologische Chemie der Universität München, Goethestraße 33, D-80336 München, Germany.49 (89) 5996 312

Translocation of nuclear-encoded preproteins across the outer membrane of mitochondria is mediated by the multicomponent transmembrane TOM complex. We have isolated the TOM core complex of Neurospora crassa by removing the receptors Tom70 and Tom20 from the isolated TOM holo complex by treatment with the detergent dodecyl maltoside. It consists of Tom40, Tom22, and the small Tom components, Tom6 and Tom7. This core complex was also purified directly from mitochondria after solubilization with dodecyl maltoside. The TOM core complex has the characteristics of the general insertion pore; it contains high-conductance channels and binds preprotein in a targeting sequence-dependent manner. It forms a double ring structure that, in contrast to the holo complex, lacks the third density seen in the latter particles. Three-dimensional reconstruction by electron tomography exhibits two open pores traversing the complex with a diameter of ~2.1 nm and a height of ~7 nm. Tom40 is the key structural element of the TOM core complex.

Key Words: TOM complex • mitochondria • protein translocation channel • electron tomography • protein targeting

© 1999 The Rockefeller University Press

Abbreviations used in this paper: 3D, three-dimensional; DHFR, dihydrofolate reductase; DDM, n-dodecyl β-D-maltoside; MSA, multivariate statistical analysis; Ni-NTA, nickel-nitrilotriacetic acid; pSu9, presequence of subunit 9 of the F0-ATPase.


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