Architecture of the mycobacterial succinate dehydrogenase with a membrane-embedded Rieske FeS cluster

Abstract

Complex II, also known as succinate dehydrogenase (SQR) or fumarate reductase (QFR), is an enzyme involved in both the Krebs cycle and oxidative phosphorylation. Mycobacterial Sdh1 has recently been identified as a new class of respiratory complex II (type F) but with an unknown electron transfer mechanism. Here, using cryoelectron microscopy, we have determined the structure of Mycobacterium smegmatis Sdh1 in the presence and absence of the substrate, ubiquinone-1, at 2.53-Å and 2.88-Å resolution, respectively. Sdh1 comprises three subunits, two that are water soluble, SdhA and SdhB, and one that is membrane spanning, SdhC. Within these subunits we identified a quinone-binding site and a rarely observed Rieske-type [2Fe-2S] cluster, the latter being embedded in the transmembrane region. A mutant, where two His ligands of the Rieske-type [2Fe-2S] were changed to alanine, abolished the quinone reduction activity of the Sdh1. Our structures allow the proposal of an electron transfer pathway that connects the substrate-binding and quinone-binding sites. Given the unique features of Sdh1 and its essential role in Mycobacteria, these structures will facilitate antituberculosis drug discovery efforts that specifically target this complex.

Impaired Succinate Oxidation Prevents Growth and Influences Drug Susceptibility in Mycobacterium tuberculosis

“…However, the growth and oxygen consumption impairments observed when Sdh2 is the only functional SDH enzyme present (i.e., when sdhA1 and frdA are transcriptionally repressed) suggest that Sdh2 is less efficient at catalyzing succinate oxidation than Sdh1. The molecular mechanisms underlying this are unclear, although both enzymes appear to use different reaction mechanisms to drive succinate oxidation ( 35 – 37 ). Moreover, these findings are in contrast to Mycobacterium smegmatis , where Sdh2 is proposed to have a higher affinity for succinate oxidation and is essential, while Sdh1 can be deleted or transcriptionally silenced with no identifiable phenotype ( 34 , 69 ).…”

“…This includes two different succinate dehydrogenase enzymes (Sdh1, Rv0249c to Rv0247c, and Sdh2, Rv3316 to Rv3319), as well as a separate fumarate reductase with possible bidirectional behavior (Frd, Rv1552 to Rv1555) ( 33 ). All three enzymes have distinct phylogenies, prosthetic groups, and predicted biochemistries ( 31 , 34 – 37 ) and are differentially expressed in M. tuberculosis ( 38 – 40 ), suggesting that these enzymes perform distinct, but overlapping, roles.…”

Structure of mycobacterial respiratory Complex I

“…These electron entry and electron exit branches can include catalysis of the same reaction by two or more apparently redundant enzymes, which complicates inhibition of the mycobacterial ETC. Previously-determined structures from the mycobacterial ETC include the succinate dehydrogenases Sdh1 (15) and Sdh2 (16) (also known as respiratory Complex II), the cytochrome aa3-bcc terminal oxidase (17)(18)(19)(20) (also known as the Complex III2IV2 respiratory supercomplex), and the cytochrome bd terminal oxidase (21,22).…”

Impaired succinate oxidation prevents growth and influences drug susceptibility in Mycobacterium tuberculosis

“…However, the growth and oxygen consumption impairments observed when Sdh2 is the only functional SDH enzyme present, suggest that Sdh2 is less efficient at catalyzing succinate oxidation than Sdh1. The molecular mechanisms underlying this are unclear, although both enzymes appear to use different reaction mechanisms to drive succinate oxidation (34–36). Moreover, these findings are in contrast to M. smegmatis where Sdh2 is proposed to have a higher affinity for succinate oxidation and is essential, while Sdh1 can be deleted with no identifiable phenotype (154).…”

“…This includes two different succinate dehydrogenase enzymes (Sdh1; Rv0249c-Rv0247c and Sdh2; Rv3316- Rv3319), as well as a separate fumarate reductase with possible bi-directional behavior (Frd; Rv1552-Rv1555) (32). All three enzymes have distinct phylogenies, prosthetic groups and predicted biochemistries (30, 33–36), and are differentially expressed in M. tuberculosis (37–39), suggesting that these enzymes perform distinct, but overlapping, roles.…”