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The active form of quinol-dependent nitric oxide reductase from Neisseria meningitidis is a dimer

DOI: 10.1107/S2052252520003656 DOI Help

Authors: M. Arif M. Jamali (University of Hyogo) , Chai C. Gopalasingam (University of Hyogo) , Rachel M. Johnson (University of Leeds) , Takehiko Tosha (RIKEN SPring-8 Center) , Kazumasa Muramoto (University of Hyogo) , Stephen P. Muench (University of Leeds) , Svetlana V. Antonyuk (University of Liverpool) , Yoshitsugu Shiro (University of Hyogo) , Samar Hasnain (University of Liverpool)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Iucrj , VOL 7 , PAGES 404 - 415

State: Published (Approved)
Published: May 2020
Diamond Proposal Number(s): 19832

Open Access Open Access

Abstract: Neisseria meningitidis is carried by nearly a billion humans, causing developmental impairment and over 100 000 deaths a year. A quinol-dependent nitric oxide reductase (qNOR) plays a critical role in the survival of the bacterium in the human host. X-ray crystallographic analyses of qNOR, including that from N. meningitidis (NmqNOR) reported here at 3.15 Å resolution, show monomeric assemblies, despite the more active dimeric sample being used for crystallization. Cryo-electron microscopic analysis of the same chromatographic fraction of NmqNOR, however, revealed a dimeric assembly at 3.06 Å resolution. It is shown that zinc (which is used in crystallization) binding near the dimer-stabilizing TMII region contributes to the disruption of the dimer. A similar destabilization is observed in the monomeric (∼85 kDa) cryo-EM structure of a mutant (Glu494Ala) qNOR from the opportunistic pathogen Alcaligenes (Achromobacter) xylosoxidans, which primarily migrates as a monomer. The monomer–dimer transition of qNORs seen in the cryo-EM and crystallographic structures has wider implications for structural studies of multimeric membrane proteins. X-ray crystallographic and cryo-EM structural analyses have been performed on the same chromatographic fraction of NmqNOR to high resolution. This represents one of the first examples in which the two approaches have been used to reveal a monomeric assembly in crystallo and a dimeric assembly in vitrified cryo-EM grids. A number of factors have been identified that may trigger the destabilization of helices that are necessary to preserve the integrity of the dimer. These include zinc binding near the entry of the putative proton-transfer channel and the preservation of the conformational integrity of the active site. The mutation near the active site results in disruption of the active site, causing an additional destabilization of helices (TMIX and TMX) that flank the proton-transfer channel helices, creating an inert monomeric enzyme.

Journal Keywords: quinol-dependent nitric oxide reductase; Neisseria meningitidis; proton transfer; cryo-electron microscopy; oligomerization

Subject Areas: Biology and Bio-materials

Diamond Offline Facilities: Electron Bio-Imaging Centre (eBIC)
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