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Eukaryotic Cell, September 2006, p. 1460-1467, Vol. 5, No. 9
1535-9778/06/$08.00+0     doi:10.1128/EC.00118-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

ND3 and ND4L Subunits of Mitochondrial Complex I, Both Nucleus Encoded in Chlamydomonas reinhardtii, Are Required for Activity and Assembly of the Enzyme

Pierre Cardol,1,2* Marie Lapaille,2 Pierre Minet,2 Fabrice Franck,1 René F. Matagne,2 and Claire Remacle2

Biochemistry and Photobiology Laboratory, Department of Life Sciences, Université de Liège, B-4000, Liège, Belgium,1 Genetics of Microorganisms Laboratory, Department of Life Sciences, Université de Liège, B-4000, Liège, Belgium2

Received 20 April 2006/ Accepted 5 July 2006

Made of more than 40 subunits, the rotenone-sensitive NADH:ubiquinone oxidoreductase (complex I) is the most intricate membrane-bound enzyme of the mitochondrial respiratory chain. In vascular plants, fungi, and animals, at least seven complex I subunits (ND1, -2, -3, -4, -4L, -5, and -6; ND is NADH dehydrogenase) are coded by mitochondrial genes. The role of these highly hydrophobic subunits in the enzyme activity and assembly is still poorly understood. In the unicellular green alga Chlamydomonas reinhardtii, the ND3 and ND4L subunits are encoded in the nuclear genome, and we show here that the corresponding genes, called NUO3 and NUO11, respectively, display features that facilitate their expression and allow the proper import of the corresponding proteins into mitochondria. In particular, both polypeptides show lower hydrophobicity compared to their mitochondrion-encoded counterparts. The expression of the NUO3 and NUO11 genes has been suppressed by RNA interference. We demonstrate that the absence of ND3 or ND4L polypeptides prevents the assembly of the 950-kDa whole complex I and suppresses the enzyme activity. The putative role of hydrophobic ND subunits is discussed in relation to the structure of the complex I enzyme. A model for the assembly pathway of the Chlamydomonas enzyme is proposed.

* Corresponding author. Mailing address: Genetics of Microorganisms Laboratory, Department of Life Sciences, Université de Liège, B-4000, Liège, Belgium. Phone: 3243663827. Fax: 3243663840. E-mail: pierre.cardol{at}ulg.ac.be.

Eukaryotic Cell, September 2006, p. 1460-1467, Vol. 5, No. 9
1535-9778/06/$08.00+0     doi:10.1128/EC.00118-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Figueroa-Martinez, F., Funes, S., Franzen, L.-G., Gonzalez-Halphen, D. (2008). Reconstructing the Mitochondrial Protein Import Machinery of Chlamydomonas reinhardtii. Genetics 179: 149-155 [Abstract] [Full Text]  
  • Torres-Bacete, J., Nakamaru-Ogiso, E., Matsuno-Yagi, A., Yagi, T. (2007). Characterization of the NuoM (ND4) Subunit in Escherichia coli NDH-1: CONSERVED CHARGED RESIDUES ESSENTIAL FOR ENERGY-COUPLED ACTIVITIES. J. Biol. Chem. 282: 36914-36922 [Abstract] [Full Text]  


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