Mrp superfamily

Last updated April 26, 2019

The Na⁺ Transporting Mrp Superfamily is a superfamily of integral membrane transport proteins.

A protein superfamily is the largest grouping (clade) of proteins for which common ancestry can be inferred. Usually this common ancestry is inferred from structural alignment and mechanistic similarity, even if no sequence similarity is evident. Sequence homology can then be deduced even if not apparent. Superfamilies typically contain several protein families which show sequence similarity within each family. The term protein clan is commonly used for protease and glycosyl hydrolases superfamilies based on the MEROPS and CAZy classification systems.

A membrane transport protein is a membrane protein involved in the movement of ions, small molecules, or macromolecules, such as another protein, across a biological membrane. Transport proteins are integral transmembrane proteins; that is they exist permanently within and span the membrane across which they transport substances. The proteins may assist in the movement of substances by facilitated diffusion or active transport. The two main types of proteins involved in such transport are broadly categorized as either channels or carriers. The solute carriers and atypical SLCs are secondary active or facilitative transporters in humans.

It includes the TC families:

2.A.63 - The Monovalent Cation (K⁺ or Na⁺):Proton Antiporter-3 (CPA3) Family

The Monovalent Cation (K⁺ or Na⁺):Proton Antiporter-3 (CPA3) Family (TC# 2.A.63) is a member of the Na⁺ transporting Mrp superfamily. The CPA3 family consists of bacterial multicomponent K⁺:H⁺ and Na⁺:H⁺ antiporters. The best characterized systems are the PhaABCDEFG system of Sinorhizobium meliloti (TC# 2.A.63.1.1) that functions in pH adaptation and as a K⁺ efflux system, and the MnhABCDEFG system of Staphylococcus aureus (TC# 2.A.63.1.3) that functions as a Na⁺ efflux Na⁺:H⁺ antiporter.

3.D.1 - The H⁺ or Na⁺-translocating NADH Dehyrogenase (NDH) Family

3.D.9 - The H⁺-translocating F₄₂₀H₂ Dehydrogenase (F₄₂₀H₂DH) Family

The H⁺-translocating F₄₂₀H₂ Dehydrogenase (F₄₂₀H₂DH) Family(TC# 3.D.9) is a member of the Na⁺ transporting Mrp superfamily. A single F₄₂₀H₂ dehydrogenase (also referred to as F₄₂₀H₂:quinol oxidoreductase) from the methanogenic archaeon, Methanosarcina mazei Gö1, has been shown to be a redox driven proton pump. The F₄₂₀H₂DH of M. mazei has a molecular size of about 120 kDa and contains Fe-S clusters and FAD. A similar five-subunit enzyme has been isolated from Methanolobus tindarius. The sulfate-reducing Archaeoglobus fulgidus (and several other archaea) also have this enzyme.

Mrp of Bacillus subtilis is a 7 subunit Na⁺/H⁺ antiporter complex (TC# 2.A.63.1.4). All subunits are homologous to the subunits in other members of this monovalent cation (K⁺ or Na⁺):proton antiporter-3 (CPA3) family as well as subunits in the archaeal hydrogenases (TC#s 3.D.1.4.1 and 3.D.1.4.2), which share several subunits with NADH dehydrogenase subunits (3.D.1). The largest subunits of the Mrp complex (MrpA and MrpD) are homologous to subunits in NADH dehydrogenases (NDHs): ND2, ND4 and ND5 in the fungal NADH dehydrogenase complex and most other NDHs, as well as subunits in the F₄₂₀H₂ dehydrogenase of Methanosarcina mazei (TC#3.D.9.1.1).^[1] These homologous subunits may catalyze Na⁺/K⁺ and/or H⁺ transport.

Bacillus subtilis, known also as the hay bacillus or grass bacillus, is a Gram-positive, catalase-positive bacterium, found in soil and the gastrointestinal tract of ruminants and humans. A member of the genus Bacillus, B. subtilis is rod-shaped, and can form a tough, protective endospore, allowing it to tolerate extreme environmental conditions. B. subtilis has historically been classified as an obligate aerobe, though evidence exists that it is a facultative anaerobe. B. subtilis is considered the best studied Gram-positive bacterium and a model organism to study bacterial chromosome replication and cell differentiation. It is one of the bacterial champions in secreted enzyme production and used on an industrial scale by biotechnology companies.

An antiporter (also called exchanger or counter-transporter) is a cotransporter and integral membrane protein involved in secondary active transport of two or more different molecules or ions across a phospholipid membrane such as the plasma membrane in opposite directions. Na⁺/H⁺ antiporters have been reviewed.

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An electron transport chain (ETC) is a series of complexes that transfer electrons from electron donors to electron acceptors via redox (both reduction and oxidation occurring simultaneously) reactions, and couples this electron transfer with the transfer of protons (H⁺ ions) across a membrane. This creates an electrochemical proton gradient that drives the synthesis of adenosine triphosphate (ATP), a molecule that stores energy chemically in the form of highly strained bonds. The molecules of the chain include peptides, enzymes (which are proteins or protein complexes), and others. The final acceptor of electrons in the electron transport chain during aerobic respiration is molecular oxygen although a variety of acceptors other than oxygen such as sulfate exist in anaerobic respiration.

A proton pump is an integral membrane protein that builds up a proton gradient across a biological membrane. Proton pumps catalyze the following reaction:

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The Transporter Classification Database is an International Union of Biochemistry and Molecular Biology (IUBMB)-approved classification system for membrane transport proteins, including ion channels.

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The sodium–hydrogen antiporter or sodium–proton exchanger (Na+/H+ exchanger) is a membrane protein that transports Na⁺ into the cell, and H⁺ out of the cell (antiport).

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Phosphate permeases are membrane transport proteins that facilitate the diffusion of phosphate into and out of a cell or organelle. Some of these families include:

The NhaB family belongs to the Ion Transporter (IT) Superfamily. A representative list of proteins belonging to the NhaB family can be found in the Transporter Classification Database.

The NhaE family belongs to the Ion Transporter (IT) Superfamily. A representative list of proteins belonging to the NhaE family can be found in the Transporter Classification Database.

The Monovalent Cation:Proton Antiporter-1 (CPA1) Family (TC# 2.A.36) is a large family of proteins derived from Gram-positive and Gram-negative bacteria, blue-green bacteria, archaea, yeast, plants and animals. The CPA1 family belongs to the VIC superfamily. Transporters from eukaryotes have been functionally characterized to catalyze Na⁺:H⁺ exchange. Their primary physiological functions are thought to be in (1) cytoplasmic pH regulation, extruding the H⁺ generated during metabolism, and (2) salt tolerance (in plants), due to Na⁺ uptake into vacuoles. Bacterial homologues have also been found to facilitate Na⁺:H⁺ antiport, but some also catalyze Li⁺:H⁺ antiport or Ca²⁺:H⁺ antiport under certain conditions.

The Monovalent Cation:Proton Antiporter-2 (CPA2) Family is a moderately large family of transporters belonging to the CPA superfamily. Members of the CPA2 family have been found in bacteria, archaea and eukaryotes. The proteins of the CPA2 family consist of between 333 and 900 amino acyl residues and exhibit 10-14 transmembrane α-helical spanners (TMSs).

The Cation:Proton Antiporter (CPA) Superfamily is a superfamily of transport proteins named after one of its constituent members, the monovalent cation:proton antiporter-2.

The Malonate:Na⁺ Symporter (MSS) Family (TC# 2.A.70) is a group of transport proteins belonging to the CPA superfamily. These proteins are composites with constituents ranging in size from 129 to 255 amino acyl residues (aas) and exhibiting 4 to 7 transmembrane segments (TMSs). A representative list of proteins belonging to the MSS family can be found in the Transporter Classification Database.

The Na⁺-transporting Carboxylic Acid Decarboxylase (NaT-DC) Family (TC# 3.B.1) is a family of porters that belong to the CPA superfamily. Members of this family have been characterized in both Gram-positive and Gram-negative bacteria. A representative list of proteins belonging to the NaT-DC family can be found in the Transporter Classification Database.

NDH-2, also known as type II NADH:quinone oxidoreductase or alternative NADH dehydrogenase, it's an enzyme which catalyzes the electron transfer from NADH to a quinone, being part of the electron transport chain. NDH-2 are peripheral membrane protein, functioning as dimers in vivo, with approximately 45 KDa per subunit and a single FAD as their cofactor.

References

↑ Zickermann, Volker; Wirth, Christophe; Nasiri, Hamid; Siegmund, Karin; Schwalbe, Harald; Hunte, Carola; Brandt, Ulrich (2015-01-02). "Structural biology. Mechanistic insight from the crystal structure of mitochondrial complex I". Science. 347 (6217): 44–49. doi:10.1126/science.1259859. ISSN 1095-9203. PMID 25554780.

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[1] Zickermann, Volker; Wirth, Christophe; Nasiri, Hamid; Siegmund, Karin; Schwalbe, Harald; Hunte, Carola; Brandt, Ulrich (2015-01-02). "Structural biology. Mechanistic insight from the crystal structure of mitochondrial complex I". Science. 347 (6217): 44–49. doi:10.1126/science.1259859. ISSN 1095-9203. PMID 25554780.

Mrp superfamily

See also

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References