| High potential iron-sulfur protein | |||||||||
|---|---|---|---|---|---|---|---|---|---|
 Structure of the oxidized high-potential iron-sulfur protein. [1] | |||||||||
| Identifiers | |||||||||
| Symbol | HIPIP | ||||||||
| Pfam | PF01355 | ||||||||
| InterPro | IPR000170 | ||||||||
| PROSITE | PDOC00515 | ||||||||
| SCOP2 | 1hpi / SCOPe / SUPFAM | ||||||||
| OPM superfamily | 116 | ||||||||
| OPM protein | 1hpi | ||||||||
| |||||||||
High potential iron-sulfur proteins (HIPIP) are a class of iron-sulfur proteins. [2] They are ferredoxins that participate in electron transfer in photosynthetic bacteria as well as in Paracoccus denitrificans .
The HiPIPs are small proteins, typically containing 63 to 85 amino acid residues. The sequences show significant variation. As shown in the following schematic representation the iron-sulfur cluster is bound by four conserved cysteine residues. [3]
[ 4Fe-4S cluster] | | | | xxxxxxxxxxxxxxxxxxxCxCxxxxxxxCxxxxxCxxxx
C: conserved cysteine residue involved in the binding of the 4Fe-4S core. [4]
The [Fe4S4] clusters are abundant cofactors of metalloproteins. [5] They participate in electron-transfer sequences. The core structure for the [Fe4S4] cluster is a cube with alternating Fe and S vertices. These clusters exist in two oxidation states with a small structural change. Two families of [Fe4S4] clusters are known: the ferredoxin (Fd) family and the high-potential iron–suflur protein (HiPIP) family. Both HiPIP and Fd share the same resting state: [Fe4S4]2+, which have the same geometric and spectroscopic features. Differences arise when it comes to their active state: HiPIP forms by oxidation to [Fe4S4]3+, and Fd is formed by reduction to [Fe4S4]+.
The different oxidation states are explained by the proteins that combined with the [Fe4S4] cluster. Analysis from crystallographic data suggests that HiPIP is capable of preserving its higher oxidation state by forming fewer hydrogen bonds with water. The characteristic fold of the proteins wraps the [Fe4S4] cluster in a hydrophobic core, only being able to form about five conserved H-bond to the cluster ligands from the backbone. In contrast, the protein associated with the Fd's allows these clusters to contact solvent resulting in 8 protein H-bonding interactions. The protein binds Fd via conserved CysXXCysXXCys structure (X stands for any amino acid). [6] Also, the unique protein structure and dipolar interactions from peptide and intermolecular water contribute to shielding the [Fe4S4]3+ cluster from the attack of random outside electron donors, which protects itself from hydrolysis.
HiPIP analogues can be synthesized by ligand exchange reactions of [Fe4S4{N(SiMe3)2}4]− with 4 equiv of thiols (HSR) as follows:
The precursor cluster [Fe4S4{N(SiMe3)2}4]− can be synthesized by one-pot reaction of FeCl3, NaN(SiMe3)2, and NaSH. The synthesis of HiPIP analogues can help people understand the factors that cause variety redox of HiPIP. [7]
HiPIPs take part in many oxidizing reactions in creatures, and are especially known with photosynthetic anaerobic bacteria, such as Chromatium , and Ectothiorhodospira . HiPIPs are periplasmic proteins in photosynthetic bacteria. They play a role of electron shuttles in the cyclic electron flow between the photosynthetic reaction center and the cytochrome bc1 complex. Other oxidation reactions HiPIP involved include catalyzing Fe(II) oxidation, being electron donor to reductase and electron accepter for some thiosulfate-oxidizing enzyme. [8]
Iron–sulfur clusters are molecular ensembles of iron and sulfide. They are most often discussed in the context of the biological role for iron–sulfur proteins, which are pervasive. Many Fe–S clusters are known in the area of organometallic chemistry and as precursors to synthetic analogues of the biological clusters. It is believed that the last universal common ancestor had many iron-sulfur clusters.
Nitrogenases are enzymes (EC 1.18.6.1EC 1.19.6.1) that are produced by certain bacteria, such as cyanobacteria (blue-green bacteria) and rhizobacteria. These enzymes are responsible for the reduction of nitrogen (N2) to ammonia (NH3). Nitrogenases are the only family of enzymes known to catalyze this reaction, which is a step in the process of nitrogen fixation. Nitrogen fixation is required for all forms of life, with nitrogen being essential for the biosynthesis of molecules (nucleotides, amino acids) that create plants, animals and other organisms. They are encoded by the Nif genes or homologs. They are related to protochlorophyllide reductase.
Photosystem I is one of two photosystems in the photosynthetic light reactions of algae, plants, and cyanobacteria. Photosystem I is an integral membrane protein complex that uses light energy to catalyze the transfer of electrons across the thylakoid membrane from plastocyanin to ferredoxin. Ultimately, the electrons that are transferred by Photosystem I are used to produce the moderate-energy hydrogen carrier NADPH. The photon energy absorbed by Photosystem I also produces a proton-motive force that is used to generate ATP. PSI is composed of more than 110 cofactors, significantly more than Photosystem II.
Ferredoxins are iron–sulfur proteins that mediate electron transfer in a range of metabolic reactions. The term "ferredoxin" was coined by D.C. Wharton of the DuPont Co. and applied to the "iron protein" first purified in 1962 by Mortenson, Valentine, and Carnahan from the anaerobic bacterium Clostridium pasteurianum.
Iron–sulfur proteins are proteins characterized by the presence of iron–sulfur clusters containing sulfide-linked di-, tri-, and tetrairon centers in variable oxidation states. Iron–sulfur clusters are found in a variety of metalloproteins, such as the ferredoxins, as well as NADH dehydrogenase, hydrogenases, coenzyme Q – cytochrome c reductase, succinate – coenzyme Q reductase and nitrogenase. Iron–sulfur clusters are best known for their role in the oxidation-reduction reactions of electron transport in mitochondria and chloroplasts. Both Complex I and Complex II of oxidative phosphorylation have multiple Fe–S clusters. They have many other functions including catalysis as illustrated by aconitase, generation of radicals as illustrated by SAM-dependent enzymes, and as sulfur donors in the biosynthesis of lipoic acid and biotin. Additionally, some Fe–S proteins regulate gene expression. Fe–S proteins are vulnerable to attack by biogenic nitric oxide, forming dinitrosyl iron complexes. In most Fe–S proteins, the terminal ligands on Fe are thiolate, but exceptions exist.
Aconitase is an enzyme that catalyses the stereo-specific isomerization of citrate to isocitrate via cis-aconitate in the tricarboxylic acid cycle, a non-redox-active process.
A hydrogenase is an enzyme that catalyses the reversible oxidation of molecular hydrogen (H2), as shown below:
Rieske proteins are iron–sulfur protein (ISP) components of cytochrome bc1 complexes and cytochrome b6f complexes and are responsible for electron transfer in some biological systems. John S. Rieske and co-workers first discovered the protein and in 1964 isolated an acetylated form of the bovine mitochondrial protein. In 1979 Trumpower's lab isolated the "oxidation factor" from bovine mitochondria and showed it was a reconstitutively-active form of the Rieske iron-sulfur protein
It is a unique [2Fe-2S] cluster in that one of the two Fe atoms is coordinated by two histidine residues rather than two cysteine residues. They have since been found in plants, animals, and bacteria with widely ranging electron reduction potentials from -150 to +400 mV.
Outer sphere refers to an electron transfer (ET) event that occurs between chemical species that remain separate and intact before, during, and after the ET event. In contrast, for inner sphere electron transfer the participating redox sites undergoing ET become connected by a chemical bridge. Because the ET in outer sphere electron transfer occurs between two non-connected species, the electron is forced to move through space from one redox center to the other.
Rubredoxins are a class of low-molecular-weight iron-containing proteins found in sulfur-metabolizing bacteria and archaea. Sometimes rubredoxins are classified as iron-sulfur proteins; however, in contrast to iron-sulfur proteins, rubredoxins do not contain inorganic sulfide. Like cytochromes, ferredoxins and Rieske proteins, rubredoxins are thought to participate in electron transfer in biological systems. Recent work in bacteria and algae have led to the hypothesis that some rubredoxins may instead have a role in delivering iron to metalloproteins.
P700, or photosystem I primary donor, is the reaction-center chlorophyll a molecular dimer associated with photosystem I in plants, algae, and cyanobacteria.
In enzymology, protochlorophyllide reductases (POR) are enzymes that catalyze the conversion from protochlorophyllide to chlorophyllide a. They are oxidoreductases participating in the biosynthetic pathway to chlorophylls.
In enzymology, carbon monoxide dehydrogenase (CODH) (EC 1.2.7.4) is an enzyme that catalyzes the chemical reaction
In enzymology, a pyruvate synthase is an enzyme that catalyzes the interconversion of pyruvate and acetyl-CoA. It is also called pyruvate:ferredoxin oxidoreductase (PFOR).
In enzymology, an ethylbenzene hydroxylase (EC 1.17.99.2) is an enzyme that catalyzes the chemical reaction
In enzymology, a ferredoxin-NADP+ reductase (EC 1.18.1.2) abbreviated FNR, is an enzyme that catalyzes the chemical reaction
In enzymology, ferredoxin hydrogenase, also referred to as [Fe-Fe]hydrogenase, H2 oxidizing hydrogenase, H2 producing hydrogenase, bidirectional hydrogenase, hydrogenase (ferredoxin), hydrogenlyase, and uptake hydrogenase, is found in Clostridium pasteurianum, Clostridium acetobutylicum,Chlamydomonas reinhardtii, and other organisms. The systematic name of this enzyme is hydrogen:ferredoxin oxidoreductase
In enzymology, a ferredoxin—nitrate reductase (EC 1.7.7.2) is an enzyme that catalyzes the chemical reaction
Ferredoxin-thioredoxin reductase EC 1.8.7.2, systematic name ferredoxin:thioredoxin disulfide oxidoreductase, is a [4Fe-4S] protein that plays an important role in the ferredoxin/thioredoxin regulatory chain. It catalyzes the following reaction:
In enzymology, an aldehyde ferredoxin oxidoreductase (EC 1.2.7.5) is an enzyme that catalyzes the chemical reaction
