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

Abstract

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.

The mitochondrial respiratory chain of the secondary green alga Euglena gracilis shares many additional subunits with parasitic Trypanosomatidae

“…In contrast, in all eukaryotes investigated so far, including T. brucei (Acestor, Zikova et al 2011), the mammal Bos taurus (Carroll et al, 2006), the yeast Yarrowia lipolytica (Angerer et al, 2011), the green alga Chlamydomonas reinhardtii (Cardol et al, 2004) and the amoeba Acanthamoeba castellanii (Gawryluk et al, 2012), CI has a molecular mass of ~900-1000 kDa. In green plants, mammals and fungi, CI has however been found in association with dimeric CIII and/or CIV, leading to supercomplexes of >1.5 MDa (Cardol et al, 2008;Dudkina et al, 2005;Schagger and Pfeiffer, 2000). However, in the present study, no evidence for the presence of CIII or CIV subunits could be obtained in the band corresponding to CI in E. gracilis.…”

Complex I Function Is Defective in Complex IV-deficient Caenorhabditis elegans

“…Conversely, the disruption of complex I function caused by nonsense mutations in NDUFS4, a subunit of this large multimeric complex, leads to the partial loss of complex III activity in skin fibroblast cultures obtained from Leigh-like patients (18,19). However, defects in the complex I subunit ND5 did not cause a loss of complex III in the I-III supercomplex (20).…”

Polyadenylation in Arabidopsis and Chlamydomonas organelles: the input of nucleotidyltransferases, poly(A) polymerases and polynucleotide phosphorylase

“…Chlamydomonas possesses a short, linear mitochondrial genome, with divergent transcription units emanating from a dual promoter/replication origin region analogous to what is found in animal mitochondrial DNAs (Cardol et al, 2008). The cox1 transcript, encoding cytochrome oxidase subunit 1, is an easily detectable mRNA, and was chosen for analysis of mitochondrial polyadenylation.…”