| Adenosinetriphosphatase | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Identifiers | |||||||||
| EC no. | 3.6.1.3 | ||||||||
| CAS no. | 9000-83-3 | ||||||||
| Databases | |||||||||
| IntEnz | IntEnz view | ||||||||
| BRENDA | BRENDA entry | ||||||||
| ExPASy | NiceZyme view | ||||||||
| KEGG | KEGG entry | ||||||||
| MetaCyc | metabolic pathway | ||||||||
| PRIAM | profile | ||||||||
| PDB structures | RCSB PDBPDBePDBsum | ||||||||
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ATPases (EC3.6.1.3,Adenosine 5'-TriPhosphatase, adenylpyrophosphatase, ATP monophosphatase, triphosphatase, ATP hydrolase, adenosine triphosphatase) are a class ofenzymes thatcatalyze thedecomposition ofATP intoADP and a freephosphate ion[1][2][3][4][5][6] or the inverse reaction. Thisdephosphorylation reaction releasesenergy, which the enzyme (in most cases) harnesses to drive otherchemical reactions that would not otherwise occur. This process is widely used in all known forms oflife.
Some such enzymes areintegral membrane proteins (anchored withinbiological membranes), and movesolutes across the membrane, typically against their concentration gradient. These are called transmembrane ATPases.
Transmembrane ATPases import metabolites necessary forcellmetabolism and export toxins, wastes, and solutes that can hinder cellular processes. An important example is thesodium-potassium pump (Na+/K+ATPase) that maintains thecell membrane potential. Another example is thehydrogen potassium ATPase (H+/K+ATPase or gastric proton pump) that acidifies the contents of the stomach. ATPase is genetically conserved in animals; therefore,cardenolides which are toxic steroids produced by plants that act on ATPases, make general and effective animal toxins that act dose dependently.[7]
Besides exchangers, other categories of transmembrane ATPase includeco-transporters and pumps (however, some exchangers are also pumps). Some of these, like the Na+/K+ATPase, cause a net flow of charge, but others do not. These are called electrogenic transporters and electroneutral transporters, respectively.[8] Genetic variants in ATPases result in a wide spectrum of human diseases, from prenatal to later onset disease.[9][10]
TheWalker motifs are a telltale protein sequence motif for nucleotide binding and hydrolysis. Beyond this broad function, the Walker motifs can be found in almost all natural ATPases, with the notable exception oftyrosine kinases.[11] The Walker motifs commonly form aBeta sheet-turn-Alpha helix that is self-organized as aNest (protein structural motif). This is thought to be because modern ATPases evolved from small NTP-binding peptides that had to be self-organized.[12]
Protein design has been able to replicate the ATPase function (weakly) without using natural ATPase sequences or structures. Importantly, while all natural ATPases have some beta-sheet structure, the designed "Alternative ATPase" lacks beta sheet structure, demonstrating that this life-essential function is possible with sequences and structures not found in nature.[13]
ATPase (also called FoF1-ATP Synthase) is a charge-transferring complex that catalyzes ATP to perform ATP synthesis by moving ions through the membrane.[14]
The coupling of ATP hydrolysis and transport is a chemical reaction in which a fixed number of solute molecules are transported for each ATP molecule hydrolyzed; for the Na+/K+ exchanger, this is three Na+ ions out of the cell and two K+ ions inside per ATP molecule hydrolyzed.
Transmembrane ATPases make use of ATP's chemical potential energy by performing mechanical work: they transport solutes in the opposite direction of their thermodynamically preferred direction of movement—that is, from the side of the membrane with low concentration to the side with high concentration. This process is referred to asactive transport.
For instance, inhibiting vesicular H+-ATPases would result in a rise in the pH within vesicles and a drop in the pH of the cytoplasm.
All of the ATPases share a common basic structure. Each rotary ATPase is composed of two major components: Fo/A0/V0 and F1/A1/V1. They are connected by 1-3 stalks to maintain stability, control rotation, and prevent them from rotating in the other direction. One stalk is utilized to transmit torque.[15] The number of peripheral stalks is dependent on the type of ATPase: F-ATPases have one, A-ATPases have two, and V-ATPases have three. The F1 catalytic domain is located on the N-side (negative-side) of the membrane and is involved in the synthesis and degradation of ATP and is involved inoxidative phosphorylation. The Fo transmembrane domain is involved in the movement of ions across the membrane.[14]
The bacterialFoF1-ATPase consists of the soluble F1 domain and the transmembrane Fo domain, which is composed of several subunits with varying stoichiometry. There are two subunits, γ, and ε, that form the central stalk and they are linked to Fo. Fo contains a c-subunit oligomer in the shape of a ring (c-ring). The α subunit is close to the subunit b2 and makes up the stalk that connects the transmembrane subunits to the α3β3 and δ subunits. F-ATP synthases are identical in appearance and function except for the mitochondrial FoF1-ATP synthase, which contains 7-9 additional subunits.[14]
Theelectrochemical potential is what causes the c-ring to rotate in a clockwise direction for ATP synthesis. This causes the central stalk and the catalytic domain to change shape. Rotating the c-ring causes three ATP molecules to be made, which then causes H+ to move from the P-side (positive-side) of the membrane to the N-side (negative-side) of the membrane. The counterclockwise rotation of the c-ring is driven by ATP hydrolysis and ions move from the N-side to the P-side, which helps to build up electrochemical potential.[14]
TheATP synthase ofmitochondria andchloroplasts is ananabolic enzyme that harnesses the energy of a transmembraneproton gradient as an energy source for adding aninorganic phosphate group to a molecule ofadenosine diphosphate (ADP) to form a molecule of adenosine triphosphate (ATP).
This enzyme works when a proton moves down the concentration gradient, giving the enzyme a spinning motion. This unique spinning motion bonds ADP and P together to create ATP.
ATP synthase can also function in reverse, that is, use energy released by ATP hydrolysis to pump protons against their electrochemical gradient.
There are different types of ATPases, which can differ in function (ATP synthesis and/or hydrolysis), structure (F-, V- and A-ATPases contain rotary motors) and in the type of ions they transport.
P-ATPases (sometime known as E1-E2 ATPases) are found in bacteria and also in eukaryotic plasma membranes and organelles. Its name is due to short time attachment of inorganic phosphate at the aspartate residues at the time of activation. Function of P-ATPase is to transport a variety of different compounds, like ions and phospholipids, across a membrane using ATP hydrolysis for energy. There are many different classes of P-ATPases, which transports a specific type of ion. P-ATPases may be composed of one or two polypeptides, and can usually take two main conformations, E1 and E2.
Authority control databases: National |
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