Abstract
Diheme-containing succinate:menaquinone oxidoreductases (Sdh) are widespread in Gram-positive bacteria but little is known about the catalytic mechanisms they employ for succinate oxidation by menaquinone. Here, we present the 2.8 Å cryo-electron microscopy structure of a Mycobacterium smegmatis Sdh, which forms a trimer. We identified the membrane-anchored SdhF as a subunit of the complex. The 3 kDa SdhF forms a single transmembrane helix and this helix plays a role in blocking the canonically proximal quinone-binding site. We also identified two distal quinone-binding sites with bound quinones. One distal binding site is formed by neighboring subunits of the complex. Our structure further reveals the electron/proton transfer pathway for succinate oxidation by menaquinone. Moreover, this study provides further structural insights into the physiological significance of a trimeric respiratory complex II. The structure of the menaquinone binding site could provide a framework for the development of Sdh-selective anti-mycobacterial drugs.
Highlights
Diheme-containing succinate:menaquinone oxidoreductases (Sdh) are widespread in Grampositive bacteria but little is known about the catalytic mechanisms they employ for succinate oxidation by menaquinone
Electrons from the compounds in food are transferred to terminal electron acceptors through the electron transport chain (ETC), which couples the translocation of protons across a membrane
Members of the complex II superfamily are identified as succinate:quinone oxidoreductases (SQRs; or succinate dehydrogenases, SDHs) or quinol:fumarate oxidoreductases (QFRs; or fumarate reductases, FRDs) according to the preferred direction of reaction[3,4]
Summary
Purification and characterization of M. smegmatis Sdh[2]. Most mycobacterial species including M. smegmatis harbor two putative genes encoding different SDHs designated Sdh[1] and Sdh[226]. The form of trimeric assembly is similar to that observed in the Escherichia coli SQR11. Each of the three assemblies contains four canonical proteins: an FAD (flavin adenine dinucleotide)-binding protein (SdhA), an ironsulfur protein (SdhB), and two membrane-anchored proteins (SdhC and SdhD), each with three transmembrane helices It could be detected by MS (Supplementary Table 1) We refer to it as SdhF because SdhE has already been used as an assembly factor of the SdhA subunit in SQR and QFR30,31. It is worth noting that the homologous sequences of SdhF subunit are mainly found in mycobacteria (Supplementary Fig. 5), which suggests that the analogs of Sdh[2] complex might be widely distributed in mycobacteria
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
