Crystal structure of mitochondrial quinol-fumarate reductase from the parasitic nematode Ascaris suum.

In the anaerobic respiratory chain of the parasitic nematode Ascaris suum, complex II couples the reduction of fumarate to the oxidation of rhodoquinol, a reverse reaction catalyzed by mammalian complex II. In this study, the first structure of anaerobic complex II of mitochondria was determined. The structure, composed of four subunits and five co-factors, is similar to that of aerobic complex II, except for an extra peptide found in the smallest anchor subunit of the A. suum enzyme. We discuss herein the structure-function relationship of the enzyme and the critical role of the low redox potential of rhodoquinol in the fumarate reduction of A. suum complex II.