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REVIEW: Structural Insight into Evolution of the Quinone Binding Site in Complex II

Elena Maklashinaa

Department of Biochemistry and Biophysics, University of California, San Francisco, CA 94143, USA

Received May 6, 2022; Revised June 9, 2022; Accepted June 10, 2022
The Complex II family encompasses membrane bound succinate:quinones reductases and quinol:fumarate reductases that catalyze interconversion of succinate and fumarate coupled with reduction and oxidation of quinone. These enzymes are found in all biological genres and share a modular structure where a highly conserved soluble domain is bound to a membrane-spanning domain that is represented by distinct variations. The current classification of the complex II family members is based on the number of subunits and co-factors in the membrane anchor (types A-F). This classification also provides insights into possible evolutionary paths and suggests that some of the complex II enzymes (types A-C) co-evolved as the whole assembly. Origin of complex II types D and F may have arisen from independent events of de novo association of the conserved soluble domain with a new anchor. Here we analyze a recent structure of Mycobacterium smegmatis Sdh2, a complex II enzyme with two transmembrane subunits and two heme b molecules. This analysis supports an earlier hypothesis suggesting that mitochondrial complex II (type C) with a single heme b may have evolved as an assembled unit from an ancestor similar to M. smegmatis Sdh2.
KEY WORDS: succinate:ubiquinone reductase, quinol:fumarate reductase, complex II, quinone binding site, cytochrome b

DOI: 10.1134/S0006297922080077