To Which Substance Does Ferredoxin Transfer an Electron

ferredoxin-NADP+ reductase
Identifiers
EC no.	1.18.one.2
CAS no.	9029-33-eight
Databases
IntEnz	IntEnz view
BRENDA	BRENDA entry
ExPASy	NiceZyme view
KEGG	KEGG entry
MetaCyc	metabolic pathway
PRIAM	contour
PDB structures	RCSB PDB PDBe PDBsum
Gene Ontology	AmiGO / QuickGO
Search PMC articles PubMed articles NCBI proteins

In enzymology, a
ferredoxin-NADP⁺
reductase
(EC 1.xviii.i.2) abbreviated
FNR, is an enzyme that catalyzes the chemical reaction

2 reduced ferredoxin + NADP⁺
+ H⁺

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⇌




{\displaystyle \rightleftharpoons }

2 oxidized ferredoxin + NADPH

The 3 substrates of this enzyme are reduced ferredoxin, NADP⁺, and H⁺, whereas its 2 products are oxidized ferredoxin and NADPH. Information technology has a flavin cofactor, FAD.

This enzyme belongs to the family unit of oxidoreductases, that use iron-sulfur proteins equally electron donors and NAD⁺
or NADP⁺
every bit electron acceptors.

This enzyme participates in photosynthesis. FNR provides a major source of NADPH for photosynthetic organisms.^[1]

Classification

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The systematic proper noun of this enzyme class is ferredoxin:NADP⁺
oxidoreductase. Other names in common employ include:

Mechanism

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During photosynthesis, electrons are removed from water and transferred to the unmarried electron carrier ferredoxin. Ferredoxin: NADP⁺
reductase and so transfers an electron from each of two ferredoxin molecules to a unmarried molecule of the 2 electron carrier NADPH.^[two]
FNR utilizes FAD, which can be in an oxidized state, single electron reduced semiquinone country, and fully reduced state to mediate this electron transfer.^[3]

FNR has an induced-fit mechanism of catalysis.^[iii]
Bounden of ferredoxin to the enzyme causes the germination of a hydrogen bond between a glutamate residue (E312) and a serine residue (S96) in the active site.^[4]
The glutamate residue is highly conserved considering it both stabilizes the semiquinone form of FAD and is a proton donor/acceptor in the reaction.^[v]
The rate limiting step of the electron transfer reaction is the release of the first oxidized ferredoxin molecule after the reduction of FAD with 1 electron.^[3]
This step is inhibited by the presence of oxidized ferredoxin and stimulated by the presence of NADP⁺.^[3]
The binding of NADP⁺
to the enzyme lowers the binding affinity of the enzyme for ferredoxin.^[6]

This reaction can besides operate in reverse to generate reduced ferredoxin, which can then be used in a variety of biosynthetic pathways. Some bacteria and algae utilize the molecule flavodoxin instead of ferredoxin equally the single electron carrier molecule to be reduced or oxidized.^[3]

Structure

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Plant-type ferredoxin: NADP⁺
reductase has two structural domains. The first domain is an antiparallel beta barrel at the amino terminus of the protein that contains the bounden domain for the FAD cofactor.^[vii]
The second domain is at the carboxyl terminus of the poly peptide and contains an blastoff helix-beta strand fold.^[7]
This terminal domain is where the NADP⁺
binds.^[8]
The active site for the enzyme occurs at the interface between the ii domains.^[9]

Binding of the enzyme to the thylakoid membrane involves a polyproline type Two helix created between 2 FNR monomers and several proline rich integral membrane proteins.^[x]

As of late 2007, 54 structures had been solved for this class of enzymes, with PDB accession codes 1B2R, 1BJK, 1BQE, 1BX0, 1BX1, 1CJC, 1E1L, 1E62, 1E63, 1E64, 1E6E, 1EWY, 1FDR, 1FNB, 1FNC, 1FND, 1FRN, 1FRQ, 1GAQ, 1GAW, 1GJR, 1GO2, 1GR1, 1H42, 1H85, 1JB9, 1OGI, 1OGJ, 1QFY, 1QFZ, 1QG0, 1QGA, 1QGY, 1QGZ, 1QH0, 1QUE, 1QUF, 1SM4, 1W34, 1W35, 1W87, 2B5O, 2BGI, 2BGJ, 2BMW, 2BSA, 2C7G, 2GQW, 2GR0, 2GR1, 2GR2, 2GR3, 2OK7, and 2OK8.

Part

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Ferredoxin: NADP⁺
reductase is the last enzyme in the transfer of electrons during photosynthesis from photosystem I to NADPH.^[2]
The NADPH is then used every bit a reducing equivalent in the reactions of the Calvin cycle.^[2]
Electron cycling from ferredoxin to NADPH only occurs in the light in part because FNR activity is inhibited in the dark.^[11]
In nonphotosynthetic organisms, the FNR primarily works in reverse to provide reduced ferredoxin for various metabolic pathways. These pathways include nitrogen fixation, terpenoid biosynthesis, steroid metabolism, oxidative stress response, and iron–sulfur protein biogenesis.^[seven]

FNR is a soluble protein that is found both complimentary in the chloroplast stroma and bound to the thylakoid membrane. This binding occurs opposite to the agile site of the enzyme and does not seem to bear on the construction of the active site or have a significant impact on the enzyme’s activeness.^[10]
When bound to the thylakoid membrane, the enzyme exists as a dimer, but when it is free in the stroma, it is monomeric.^[10]
The binding of the FNR to the integral membrane proteins on the thylakoid membrane is enhanced under acidic conditions, so recruitment and binding of FNR to the thylakoid membrane may be a method of storing and stabilizing the enzyme in the dark when photosynthesis is not occurring.^[12]
The chloroplast stroma varies from being slightly acidic in the dark to more than alkaline metal in the light.^[ten]
Therefore, in the dark, more than FNRs would be recruited and leap to the thylakoid membrane, and in the calorie-free, more FNRs would dissociate from the membrane and exist costless in the stroma.

Development

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Ferredoxin NADP⁺
reductases are nowadays in many organisms, including plants, bacteria, and the mitochondria of eukaryotes. Yet, these proteins belong to two unrelated protein families and are an example of convergent development.^[vii]
[13]
The plant-blazon FNRs (InterPro:IPR015701, InterPro:IPR033892) include the plastidic FNRs seen in plants.^[7]
[13]
The glutathione-reductase-blazon FNRs (InterPro:IPR022890, InterPro:IPR021163), sometimes named adrenodoxin-NADP+ reductase for stardom, are seen in the mitochondria of eukaryotes.^{[vii]
[thirteen]}
Both families are seen in bacteria. Two actress families, i thioredoxin reductase-like (TRLF) and the other with a unique mechanism (NfnAB), has been identified.^[14]

In the establish-similar family unit of FNRs, selective evolutionary force per unit area has led to differences in the catalytic efficiency of FNRs in photosynthetic and nonphotosynthetic organisms. Electron transfer by FNR is a rate limiting footstep in photosynthesis, and so the plastidic FNR in plants have evolved to exist highly efficient.^[viii]
These plastidic FNRs are xx–100 fold more agile than bacterial FNRs.^[xv]
This higher catalytic efficiency of the transfer of electrons from FAD to NADP⁺
is related to structural changes in the active site that reduce the distance between the N5 in FAD and the C4 in NADP⁺.^[16]
The plastidic FNRs in plants have besides evolved to accept a high degree of substrate specificity for NADP⁺
over NAD⁺; studies of amino acid mutations have shown that the final tyrosine remainder in plastidic FNRs plays a fundamental role in this substrate specificity.^[8]
In contrast, some nonphotosynthetic FNRs exercise not preferentially bind NADP⁺
and lack this tyrosine residue.^[16]

Affliction relevance

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Several major human being diseases are caused by the obligate intracellular protozoan parasites in the phylum Apicomplexa. The apicoplast organelle in these organisms is believed to have come from an endosymbiotic event in which an ancestral protozoan engulfed an algal cell.^[7]
These apicoplasts contain plant-like FNRs that the protozoan uses to generate reduced ferredoxin, which is so used as a reductant in essential biosynthetic pathways.^[17]
FNRs from two major parasites affecting humans,
Plasmodium falciparum, which causes malaria, and
Toxoplasma gondii, which causes toxoplasmosis, have been sequenced.^[18]
Since humans do not have a homologous protein, these enzymes are possible new targets for drug therapies confronting these diseases.^[18]

References

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Further reading

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External links

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• 
  Media related to Ferredoxin—NADP(+) reductase at Wikimedia Commons