Subsystem: Respiratory Complex I

This subsystem's description is:

The proton-pumping NADH:ubiquinone oxidoreductase, which is also called respiratory complex I, transfers electrons from NADH to ubiquinone via one flavin mononucleotide (FMN) and up to nine iron-sulfur clusters.Respiratory chain Complex I or NADH:quinone oxidoreductase catalyzes oxidation of NADH in the mitochondrial matrix or bacterial cytoplasm and reduction of quinone in the membrane, coupled to pumping of 4H(+)/2e(-) across the membrane. The same enzyme complex is also capable of the reverse reaction, i.e. Deltamu(H(+))-supported NAD(+) reduction.
A structural minimal form of complex I consisting of 14 (13 inE.coli)different subunits called NuoA to NuoN (or Nqo1 to Nqo14). The isolated Escherichia coli complex I can be split into a NADH dehydrogenase fragment, a connecting fragment, and a membrane fragment. The soluble NADH dehydrogenase fragment represents the electron input part of the complex and consists of the subunits NuoE, F, and G.(Uhlmann, Friedrich,Biochemistry. 2005 Feb 8;44(5):1653-8.)The FMN and four iron-sulfur clusters have been detected in this fragment .Two EPR-detectable [4Fe-4S] clusters are bound to the NuoI in from Rhodobacter capsulatus. NuoB was shown to carry FeS cluster in E.coli.
NuoB, NuoD, NuoC constitute connecting module of complex I. Role of NuoC is not studied well.
NuoH subunit is seemingly involved in quinone binding (Roth, Hagerhall,Biochim Biophys Acta. 2001 Apr 2;1504(2-3):352-62). NuoD, NuoB interface was also shown to be involvd in quinone binding (Prieur et al,Biochim Biophys Acta. 2001 Apr 2;1504(2-3):173-8. )
6-8 membrane domain subunits considered to be involved in H(+)(Na(+)) translocation: NuoA, NuoL, NuoM, NuoN,NuoK, NuoJ, The Complex I enzyme has evolved from smaller functional building blocks. Three Complex I protein subunits, NuoL, NuoM and NuoN, show primary sequence similarity to one particular class of antiporters.Multisubunit antiporter complex is suposed to be recruited to the ancestral enzyme. It was also concluded that the last common ancestor of the Complex I enzyme family and membrane bound NiFe hydrogenases of type 3 and 4 contained the NuoKLMN subunit module.(Mathiesen, Hagerhall,FEBS Lett. 2003 Aug 14;549(1-3):7-13.)
Module organisation of Complex I is reflected in engaging of its subuits and blocks of subunits in different protein complexes in many orgnisms. It is still unclear whether the cyanobacterial ndh gene products actually form a single large protein complex or exist as smaller independent complexes. For example, paralogs of Subunits 4 and 5 are involved in carboxysome CO2 uptake and NuoE homolog (HoxE), is part of the bidirectional hydrogenase in Cyanobacteria. (Schmitz et al, Biochim Biophys Acta. 2002 Apr 22;1554(1-2):66-74). We also noticed, that NUOE is a potential component of hydrogenase in Bacteroides thetaiotaomicron VPI-5482 [B](gene clustering evidence).

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Literature ReferencesChloroplast NDH: A different enzyme with a structure similar to that of respiratory NADH dehydrogenase. Shikanai T Biochimica et biophysica acta 2016 Jul26519774
The NADH:ubiquinone oxidoreductase (complex I) from Escherichia coli. Friedrich T Biochimica et biophysica acta 1998 May 69593861
Isolation and characterization of the proton-translocating NADH: ubiquinone oxidoreductase from Escherichia coli. Leif H European journal of biochemistry 1995 Jun 17607227
EPR signals assigned to Fe/S cluster N1c of the Escherichia coli NADH:ubiquinone oxidoreductase (complex I) derive from cluster N1a. Uhlmann M Biochemistry 2005 Feb 815683249
Role of subunit NuoL for proton translocation by respiratory complex I. Steimle S Biochemistry 2011 Apr 2621417432
DiagramFunctional RolesSubsystem SpreadsheetDescriptionAdditional Notes 

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