A ferredoxin bridge connects the two arms of plant mitochondrial complex I

Abstract

Mitochondrial complex I is the main site for electron transfer to the respiratory chain and generates much of the proton gradient across the inner mitochondrial membrane. It is composed of two arms, which form a conserved L-shape. We report the structures of the intact, 47-subunit mitochondrial complex I from Arabidopsis thaliana and from the green alga Polytomella sp. at 3.2 and 3.3 [A] resolution. In both, a heterotrimeric {gamma}-carbonic anhydrase domain is attached to the membrane arm on the matrix side. Two states are resolved in A. thaliana complex I, with different angles between the two arms and different conformations of the ND1 loop near the quinol binding site. The angle appears to depend on a bridge domain, which links the peripheral arm to the membrane arm and includes an unusual ferredoxin. We suggest that the bridge domain regulates complex I activity. One sentence summaryThe activity of complex I depends on the angel between its two arms, which, in plants, is adjusted by a protein bridge that includes an unusual ferredoxin. The authors responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantcell.org) are: Hans-Peter Braun (braun@genetik.uni-hannover.de) and Werner Kuhlbrandt (werner.kuehlbrandt@biophys.mpg.de).