In Chlamydomonas, the loss of ND5 subunit prevents the assembly of whole mitochondrial complex I and leads to the formation of a low abundant 700 kDa subcomplex.
In the green alga Chlamydomonas reinhardtii, a mutant deprived of complex I enzyme activity presents a 1T deletion in the mitochondrial nd5 gene. The loss of the ND5 subunit prevents the assembly of the 950 kDa whole complex I. Instead, a low abundant 700 kDa subcomplex, loosely associated to the inner mitochondrial membrane, is assembled. The resolution of the subcomplex by SDS-PAGE gave rise to 19 individual spots, sixteen having been identified by mass spectrometry analysis. Eleven, mainly associated to the hydrophilic part of the complex, are homologs to subunits of the bovine enzyme whereas five (including gamma-type carbonic anhydrase subunits) are specific to green plants or to plants and fungi. None of the subunits typical of the beta membrane domain of complex I enzyme has been identified in the mutant. This allows us to propose that the truncated enzyme misses the membrane distal domain of complex I but retains the proximal domain associated to the matrix arm of the enzyme. A complex I topology model is presented in the light of our results. Finally, a supercomplex most probably corresponding to complex I-complex III association, was identified in mutant mitochondria, indicating that the missing part of the enzyme is not required for the formation of the supercomplex.
Cardol
Pierre
P
Genetics of Microorganisms, Department of Life Sciences, B22, University of Liège, B-4000 Liège, Belgium. pierre.cardol@ulg.ac.be
Boutaffala
Layla
L
Memmi
Samy
S
Devreese
Bart
B
Matagne
René Fernand
RF
Remacle
Claire
C
D000595:Amino Acid Sequence; D000818:Animals; D029681:Arabidopsis Proteins / Q000737:chemistry; D001426:Bacterial Proteins / Q000737:chemistry; D016825:Chlamydomonas reinhardtii / Q000737:chemistry* / Q000235:genetics; D029721:Drosophila Proteins / Q000737:chemistry; D042967:Electron Transport Complex I / Q000235:genetics / Q000378:metabolism*; D014450:Electron Transport Complex III / Q000096:biosynthesis; D042201:Magnetospirillum / Q000737:chemistry; D021122:Protein Subunits; D016415:Sequence Alignment; D053719:Tandem Mass Spectrometry
D029681:Arabidopsis Proteins; D001426:Bacterial Proteins; D029721:Drosophila Proteins; D021122:Protein Subunits; D042967:Electron Transport Complex I; D014450:Electron Transport Complex III