Subunit Arithmetic

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Science  08 Apr 2005:
Vol. 308, Issue 5719, pp. 167
DOI: 10.1126/science.308.5719.167a

The largest and least well-described (in structural terms) of the five respiratory enzyme complexes in mammalian mitochondria is the NADH:ubiquinone oxidoreductase, also known as complex I. Only recently has it been determined that the number of distinct subunits is 46, in comparison to 30 and 14 for the corresponding complex I orthologs in plants and bacteria, respectively. Applying a comparative genomic analysis using both nuclear and organellar sequence data, Gabaldón et al. show that complex I in the eukaryotic ancestor of the fungi, plants, and metazoa had grown to 35 subunits from the simpler bacterial/archaeal core, having added subunits that came along as the endosymbiont was acquired and stabilized and gaining new recruits from the host. In the subsequent eukaryotic radiation, more subunits have been added to and subtracted from all over the complex, as judged by the three-dimensional maps generated from biochemical and electron microscopic studies. This piecemeal aggrandizement contrasts with the modular assembly of existing multisubunit enzymes into the prokaryotic complex I. — GJC

J. Mol. Biol. 10.1016/j.jmb.2005.02.067 (2005).

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