The Functions and Components of the Anaerobic Respiratory Electron Transport Systems in Rhodobacter Capsulatus

ABSTRACT We have recently established that the facultative phototrophic bacterium Rhodobacter sphaeroides, like the closely relatedRhodobacter capsulatus species, contains both the previously characterized mobile electron carrier cytochromec 2 (cyt c 2) and the more recently discovered membrane-anchored cytc y. However, R. sphaeroides cytc y, unlike that of R. capsulatus, is unable to function as an efficient electron carrier between the photochemical reaction center and the cyt bc 1complex during photosynthetic growth. Nonetheless, R. sphaeroides cyt c y can act at least in R. capsulatus as an electron carrier between the cytbc 1 complex and thecbb 3-type cyt c oxidase (cbb 3-Cox) to support respiratory growth. Since R. sphaeroides harbors both acbb 3-Cox and anaa 3-type cyt c oxidase (aa 3-Cox), we examined whetherR. sphaeroides cyt c y can act as an electron carrier to either or both of these respiratory terminal oxidases. R. sphaeroides mutants which lacked either cyt c 2 or cyt c y and either the aa 3-Cox or thecbb 3-Cox were obtained. These double mutants contained linear respiratory electron transport pathways between the cyt bc 1 complex and the cytc oxidases. They were characterized with respect to growth phenotypes, contents of a-, b-, andc-type cytochromes, cyt c oxidase activities, and kinetics of electron transfer mediated by cytc 2 or cyt c y. The findings demonstrated that both cyt c 2 and cytc y are able to carry electrons efficiently from the cyt bc 1 complex to either thecbb 3-Cox or theaa 3-Cox. Thus, no dedicated electron carrier for either of the cyt c oxidases is present in R. sphaeroides. However, under semiaerobic growth conditions, a larger portion of the electron flow out of the cytbc 1 complex appears to be mediated via the cytc 2-to-cbb 3-Coxand cytcy -to-cbb 3-Coxsubbranches. The presence of multiple electron carriers and cytc oxidases with different properties that can operate concurrently reveals that the respiratory electron transport pathways of R. sphaeroides are more complex than those ofR. capsulatus.

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Cryo-EM Structures of Respiratory bc1-cbb3 type CIII2CIV Supercomplex and Electronic Communication Between the Complexes

10.1101/2020.06.27.175620 ◽

2020 ◽

Author(s):

Stefan Steimle ◽

Trevor VanEeuwen ◽

Yavuz Ozturk ◽

Hee Jong Kim ◽

Merav Braitbard ◽

...

Keyword(s):

Electron Transfer ◽

Electron Transport ◽

Rhodobacter Capsulatus ◽

Structural Features ◽

Complex Iii ◽

Transport Pathways ◽

Gram Negative ◽

Atp Production ◽

Growth Modes ◽

Respiratory Electron Transport

AbstractThe respiratory electron transport complexes convey electrons from nutrients to oxygen and generate a proton-motive force used for energy (ATP) production in cells. These enzymes are conserved among organisms, and organized as individual complexes or combined forming large super-complexes (SC). Bacterial electron transport pathways are more branched than those of mitochondria and contain multiple variants of such complexes depending on their growth modes. The Gram-negative species deploy a mitochondrial-like cytochrome bc1 (Complex III, CIII2), and may have bacteria-specific cbb3-type cytochrome c oxidases (Complex IV, CIV) in addition to, or instead of, the canonical aa3-type CIV. Electron transfer between these complexes is mediated by two different carriers: the soluble cytochrome c2 which is similar to mitochondrial cytochrome c and the membrane-anchored cytochrome cy which is unique to bacteria. Here, we report the first cryo-EM structure of a respiratory bc1-cbb3 type SC (CIII2CIV, 5.2Å resolution) and several conformers of native CIII2 (3.3Å resolution) from the Gram-negative bacterium Rhodobacter capsulatus. The SC contains all catalytic subunits and cofactors of CIII2 and CIV, as well as two extra transmembrane helices attributed to cytochrome cy and the assembly factor CcoH. Remarkably, some of the native CIII2 are structural heterodimers with different conformations of their [2Fe-2S] cluster-bearing domains. The unresolved cytochrome c domain of cy suggests that it is mobile, and it interacts with CIII2CIV differently than cytochrome c2. Distance requirements for electron transfer suggest that cytochrome cy and cytochrome c2 donate electrons to heme cp1 and heme cp2 of CIV, respectively. For the first time, the CIII2CIV architecture and its electronic connections establish the structural features of two separate respiratory electron transport pathways (membrane-confined and membrane-external) between its partners in Gram-negative bacteria.

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Advances in Bacterial Electron Transport Systems and Their Regulation

10.1016/s0065-2911(16)x0002-1 ◽

2016 ◽

Keyword(s):

Electron Transport ◽

Transport Systems

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Electron Transport Systems for Quinohemoprotein Type II Alcohol Dehydrogenase of Pseudomonas Putida HK5

Biochemistry and Molecular Biology of Vitamin B6 and PQQ-dependent Proteins ◽

10.1007/978-3-0348-8397-9_36 ◽

2000 ◽

pp. 219-224 ◽

Cited By ~ 2

Author(s):

Kazunobu Matsushita ◽

Tetsuo Yamashita ◽

Nahoko Aoki ◽

Hirohide Toyama ◽

Osao Adachi

Keyword(s):

Electron Transport ◽

Alcohol Dehydrogenase ◽

Pseudomonas Putida ◽

Transport Systems ◽

Type Ii

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Comparative studies on succinate and terminal oxidase activity in microbial and mammalian electron-transport systems

Canadian Journal of Microbiology ◽

10.1139/m69-139 ◽

1969 ◽

Vol 15 (7) ◽

pp. 797-807 ◽

Cited By ~ 17

Author(s):

Peter Jurtshuk ◽

Ann K. May ◽

Leodocia M. Pope ◽

Patricia R. Aston

Keyword(s):

Electron Transport ◽

Cytochrome C ◽

Comparative Studies ◽

Azotobacter Vinelandii ◽

Transport Systems ◽

Terminal Oxidase ◽

Succinate Oxidation ◽

State Reduction ◽

Hydroxy Quinoline ◽

Terminal Oxidation

A comparative study was undertaken to examine the succinate and terminal oxidase activities of the electron-transport systems of Azotobacter vinelandii and mammalian mitochondria. For succinate oxidation, both systems exhibited similar relative specificities for the electron acceptors phenazine methosulfate, O2, methylene blue, K3Fe(CN)6, nitrotetrazolium blue, 2,6-dichlorophenolindophenol (DCIP), and cytochrome c. They differed in that DCIP and cytochrome c were less active in the Azotobacter electron-transport system (R3 fraction) than in the bovine mitochondrial system. Comparative studies with known inhibitors of mammalian mitochondrial electron-transport demonstrated that the succinoxidase activity of the Azotobacter R3 fraction was, at least, 2000 times less sensitive to antimycin A, 700 times less sensitive to thenoyl-trifluoroacetone, and 30 times less sensitive to 2-n-heptyl-4-hydroxy-quinoline-N-oxide. Both systems were equally sensitive to KCN, p-chloromercuribenzoic acid, and chlorpromazine.The ability of the two systems to use tetramethyl-p-phenylenediamine (TMPD) and its derivatives as electron donors, for terminal oxidation, was also similar. Studies on steady state reduction revealed that in the Azotobacter R3 fraction, the cytochromes (a2, a1, b1, c4 + c5) and flavoprotein components were reduced substantially by succinate as well as by TMPD in the presence of ascorbate. Ultrastructure analyses of the Azotobacter R3 electron-transport fraction revealed the vesicular membranous components identified as oxidosomes according to the terminology used by DeLey and contained spherical headpiece units of 80 Å in diameter which appeared to be morphologically identical with the tripartite units or the elementary particles described by Green and associates, viz., Kopaczyk et al., and by Fernandez-Moran et al.

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