Tina Iverson
Last active: 4/1/2019

The unassembled flavoprotein subunits of human and bacterial complex II have impaired catalytic activity and generate only minor amounts of ROS.

Maklashina E, Rajagukguk S, Iverson TM, Cecchini G
J Biol Chem. 2018 293 (20): 7754-7765

PMID: 29610278 · PMCID: PMC5961047 · DOI:10.1074/jbc.RA118.001977

Complex II (SdhABCD) is a membrane-bound component of mitochondrial and bacterial electron transport chains, as well as of the TCA cycle. In this capacity, it catalyzes the reversible oxidation of succinate. SdhABCD contains the SDHA protein harboring a covalently bound FAD redox center and the iron-sulfur protein SDHB, containing three distinct iron-sulfur centers. When assembly of this complex is compromised, the flavoprotein SDHA may accumulate in the mitochondrial matrix or bacterial cytoplasm. Whether the unassembled SDHA has any catalytic activity, for example in succinate oxidation, fumarate reduction, reactive oxygen species (ROS) generation, or other off-pathway reactions, is not known. Therefore, here we investigated whether unassembled SdhA flavoprotein, its homolog fumarate reductase (FrdA), and the human SDHA protein have succinate oxidase or fumarate reductase activity and can produce ROS. Using recombinant expression in , we found that the free flavoproteins from these divergent biological sources have inherently low catalytic activity and generate little ROS. These results suggest that the iron-sulfur protein SDHB in complex II is necessary for robust catalytic activity. Our findings are consistent with those reported for single-subunit flavoprotein homologs that are not associated with iron-sulfur or heme partner proteins.

MeSH Terms (12)

Bacterial Proteins Catalysis Crystallography, X-Ray Electron Transport Complex II Escherichia coli Flavoproteins Humans Models, Molecular Oxidation-Reduction Protein Conformation Protein Subunits Reactive Oxygen Species

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