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MBC in Press, published online ahead of print November 3, 2004
Mol. Biol. Cell 10.1091/mbc.E04-09-0807

A more recent version of this article appeared on January 1, 2005
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Submitted on September 15, 2004
Revised on October 21, 2004
Accepted on October 26, 2004

Formation of Membrane-bound Ring Complexes by Prohibitins in Mitochondria

Takashi Tatsuta,* Kirstin Model,*{dagger} and Thomas Langer*{ddagger}

*Institut für Genetik and Zentrum für Molekulare Medizin, Universität zu Köln, 50674 Köln, Germany; {dagger}Max-Planck-Institut für Biophysik, Abteilung für Strukturbiologie, 60439 Frankfurt am Main, Germany

Monitoring Editor: Janet Shaw

Prohibitins comprise a remarkably conserved protein family in eukaryotic cells with proposed functions in cell cycle progression, senescence, apoptosis and the regulation of mitochondrial activities. Two prohibitin homologues, Phb1 and Phb2, assemble into a high molecular weight complex of ~1.2 MDa in the mitochondrial inner membrane, but a nuclear localization of Phb1 and Phb2 has also been reported. Here, we have analyzed the biogenesis and structure of the prohibitin complex in S. cerevisiae. Both Phb1 and Phb2 subunits are targeted to mitochondria by unconventional noncleavable targeting sequences at their amino terminal end. Membrane insertion involves binding of newly imported Phb1 to Tim8/13-complexes in the intermembrane space and is mediated by the TIM23-translocase. Assembly occurs via intermediate-sized complexes of ~120 kDa containing both Phb1 and Phb2. Conserved carboxy terminal coiled-coil regions in both subunits mediate the formation of large assemblies in the inner membrane. Single particle electron microscopy of purified prohibitin complexes identifies diverse ring-shaped structures with outer dimensions of ~270 Å x 200 Å. Implications of these findings for proposed cellular activities of prohibitins are discussed.

{ddagger}Corresponding author. E-mail: Thomas.Langer{at}uni-koeln.de






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