Editing Neisseria gonorrhoeae (section)

=== Electron transport chain and oxidative phosphorylation ===
As an obligate human pathogen and a facultative anaerobic [[capnophile]], ''Neisseria gonorrhoeae'' typically colonize mucosal surfaces in microaerobic environments, such as those in the genitourinary tract.<ref name="Green_2022" /> Growth in areas where oxygen concentrations are limited requires a terminal oxidase with a high affinity for oxygen; in gonococci, oxygen reduction is performed by a ''ccb<sub>3</sub>'' -type cytochrome oxidase. In addition to [[aerobic respiration]], gonococci can also perform [[anaerobic respiration]] via the reduction of nitrite (NO<sub>2</sub>) to nitric oxide (NO) as well as reduction of NO to nitrous oxide (N<sub>2</sub>O).<ref name="Green_2022" /><ref name="Li_2010">{{cite journal | vauthors = Li Y, Hopper A, Overton T, Squire DJ, Cole J, Tovell N | title = Organization of the electron transfer chain to oxygen in the obligate human pathogen Neisseria gonorrhoeae: roles for cytochromes c4 and c5, but not cytochrome c2, in oxygen reduction | journal = Journal of Bacteriology | volume = 192 | issue = 9 | pages = 2395–2406 | date = May 2010 | pmid = 20154126 | pmc = 2863483 | doi = 10.1128/JB.00002-10 }}</ref>

There are several enzymes that contribute electrons to the intramembranous ubiquinone pool, the first step in the ETC. These include the membrane bound LDHs (LldD and LdhD), [[Respiratory complex I|NADH:ubiquinone oxidoreductase]] (aka NADH dehydrogenase; Nuo complex I), Na<sup>+</sup>-translocating NADH dehydrogenase (Nqr), [[succinate dehydrogenase]] (SDH), and the membrane-bound NAD<sup>+</sup>-independent malate:quinone-oxidoreductase (MqR).<ref name="Green_2022" />

Following the initial transfer of electrons to ubiquinone, proposed schematics for the organization of the gonococcal ETC suggest the electrons can be further passed down the chain by reduction of the [[Coenzyme Q – cytochrome c reductase|cytochrome ''bc<sub>1</sub>'' complex]] or can be directly transferred to NO as a terminal electron acceptor by [[Nitric-oxide reductase|NO reductase]] (NorB).<ref name="Green_2022" /><ref name="Aspholm_2010">{{cite journal | vauthors = Aspholm M, Aas FE, Harrison OB, Quinn D, Vik A, Viburiene R, Tønjum T, Moir J, Maiden MC, Koomey M | title = Structural alterations in a component of cytochrome c oxidase and molecular evolution of pathogenic Neisseria in humans | journal = PLOS Pathogens | volume = 6 | issue = 8 | pages = e1001055 | date = August 2010 | pmid = 20808844 | pmc = 2924362 | doi = 10.1371/journal.ppat.1001055 | doi-access = free }}</ref> In the case of the former, electrons can then be passed from the ''bc<sub>1</sub>'' complex along two alternative pathways via the reduction of either cytochrome ''c<sub>4</sub>'' or ''c<sub>5</sub>''. Both of these cytochromes  transfer electrons to the terminal cytochrome ''ccb<sub>3</sub>'' oxidase for the reduction of O<sub>2</sub> to form H<sub>2</sub>O under aerobic conditions.<ref name="Green_2022" /><ref name="Li_2010" />

Gonococci are also reduce NO<sub>2</sub> via an inducible outer membrane-attached copper-containing [[nitrite reductase]] (AniA, a member of the NirK protein family) under anaerobic conditions, though this process has also been noted in microaerobic conditions as a means of supplementing growth.<ref name="Aspholm_2010" /> This leads to the formation of NO that is subsequently reduced to N<sub>2</sub>O in a partial denitrification pathway.<ref name="Green_2022" /><ref name="Li_2010" /><ref name="Aspholm_2010" /> The ''ccb<sub>3</sub>'' oxidase of ''N. gonorrhoeae'', dissimilarly to other members of the ''Neisseria'' genus, is a tri-heme protein that can transfer electrons not only to O<sub>2</sub> (conserved across ''Neisseria'' species) but also to AniA for NO<sub>2</sub> reduction. This is in addition to the typical process of receiving electrons transferred from cytochrome ''c<sub>5</sub>''.<ref name="Aspholm_2010" /><ref>{{cite journal |last1=Hopper |first1=Amanda |last2=Tovell |first2=Nicholas |last3=Cole |first3=Jeffrey |title=A physiologically significant role in nitrite reduction of the CcoP subunit of the cytochrome oxidase cbb 3 from Neisseria gonorrhoeae |journal=FEMS Microbiology Letters |date=December 2009 |volume=301 |issue=2 |pages=232–240 |doi=10.1111/j.1574-6968.2009.01824.x |pmid=19889029 }}</ref>

The general purpose of the ETC is the formation of the electrochemical gradient of hydrogen ions (H<sup>+</sup> or protons), resulting from concentration differences across the plasma membrane, needed to power ATP production in a process known as [[oxidative phosphorylation]].<ref name="Bacterial electron transport chains">{{cite journal | vauthors = Anraku Y | title = Bacterial electron transport chains | journal = Annual Review of Biochemistry | volume = 57 | issue = 1 | pages = 101–132 | date = June 1988 | pmid = 3052268 | doi = 10.1146/annurev.bi.57.070188.000533 }}</ref> In gonococci, movement of protons into the periplasmic space is accomplished by the Nuo complex I, the cytochrome ''bc<sub>1</sub>'' complex, and cytochrome ''ccb<sub>3</sub>''.<ref name="Green_2022" /><ref name="Aspholm_2010" /><ref name="Cytochrome bc1 complexes of microor">{{cite journal | vauthors = Trumpower BL | title = Cytochrome bc1 complexes of microorganisms | journal = Microbiological Reviews | volume = 54 | issue = 2 | pages = 101–129 | date = June 1990 | pmid = 2163487 | pmc = 372766 | doi = 10.1128/mr.54.2.101-129.1990 }}</ref> Subsequently, ATP synthesis is performed by the [[ATP synthase|F<sub>1</sub>F<sub>0</sub> ATP synthase]], a two-part protein complex present in gonococci as well as numerous other species across phylogenetic domains.<ref name="UniProt">{{Cite web |title=UniProt |url=https://www.uniprot.org/uniprotkb/Q5F4Z4/entry |access-date=2024-11-18 |website=www.uniprot.org}}</ref> This complex couples proton translocation back into the cytoplasm along its gradient with mechanical rotation to generate ATP.<ref name="Mechanism of the F1F0-type ATP">{{cite journal | vauthors = Capaldi RA, Aggeler R | title = Mechanism of the F(1)F(0)-type ATP synthase, a biological rotary motor | journal = Trends in Biochemical Sciences | volume = 27 | issue = 3 | pages = 154–160 | date = March 2002 | pmid = 11893513 | doi = 10.1016/s0968-0004(01)02051-5 }}</ref>