The reducible complexity of a mitochondrial molecular machine

doi:10.1073/pnas.0908264106

The reducible complexity of a mitochondrial molecular machine

^aDepartment of Biochemistry and Molecular Biology, Monash University, Clayton 3800, Australia;
^bDepartments of Biochemistry and Molecular Biology and
^fMicrobiology and Immunology and
^cBio21 Molecular Science and Biotechnology Institute, University of Melbourne, Parkville 3010 Australia;
^dDepartment of Molecular, Cellular and Developmental Biology, Yale University, New Haven, CT 06520; and
^eHoward Hughes Medical Institute, New Haven, CT 06520

Communicated by Roy Curtiss III, Arizona State University, Tempe, AZ, July 24, 2009
↵¹A.C. and D.B. contributed equally to this work. (received for review May 11, 2009)

Abstract

Molecular machines drive essential biological processes, with the component parts of these machines each contributing a partial function or structural element. Mitochondria are organelles of eukaryotic cells, and depend for their biogenesis on a set of molecular machines for protein transport. How these molecular machines evolved is a fundamental question. Mitochondria were derived from an α-proteobacterial endosymbiont, and we identified in α-proteobacteria the component parts of a mitochondrial protein transport machine. In bacteria, the components are found in the inner membrane, topologically equivalent to the mitochondrial proteins. Although the bacterial proteins function in simple assemblies, relatively little mutation would be required to convert them to function as a protein transport machine. This analysis of protein transport provides a blueprint for the evolution of cellular machinery in general.

Footnotes

²To whom correspondence should be addressed. E-mail: trevor.lithgow{at}med.monash.edu.au
Author contributions: A.C. and T.L. designed research; A.C., D.B., X.G., A.J.P., S.C., N.C., V.A.L., S.P., and C.J.-W. performed research; D.B., A.J.P., and R.A.S. contributed new reagents/analytic tools; T.L. analyzed data; and A.C., C.J.-W., R.A.S., and T.L. wrote the paper.
The authors declare no conflict of interest.
This article contains supporting information online at www.pnas.org/cgi/content/full/0908264106/DCSupplemental.