Structural Biochemistry/Membrane Proteins/P-Type ATPases
P-type ATPases are a family of cation transport enzymes present in eukaryotes,archea and bacteria. These alpha helical bundle primary transportser (P-type ATPases) are known for catalysis of self phosphorylation of a key conserved aspartate residue within an ion pump. They generate essential ion gradients that are the basis for a variety of cellular functions like signaling, energy storage and secondary transport. Prominent examples of P-type ATPases are the sodium-potassium pump(Na+,K+-ATPase), the proton pump (H+-ATPase), the proton-potassium pump (H+,K+-ATPase) and the calcium pump (Ca2+-ATPase).
Discovered in 1957 by Nobel Laureate Jens Christian Skou, the first P-type ATPase was the Na+, K+ - ATPase. As of June 2007, 400 unique and confirmed members of the P-type ATPase family have been discovered.
These enzymes have a significant impact on cellular funciton. Indeed, more than one third of the ATP consumed by a resting animal is used by a single ion pump, the Na+,K+-ATPase. The calcium pump (located in the sarcoplasmic reticulum (SR) membrane) also plays a significant role because it is responsible for pumping calcium from the muscle cell to cause a muscle to relax.
P-type ATPases can be divided into five phylogenetic subfamilies:
•Type I—Transition/heavy metal ATPases. These ATPases are involved in transport of metals such as K+, Cu+, Ag+, Cu2+, Zn2+, Cd2+, Pb2+ and Co2+.
•Type II—Includes Ca2+-ases, such as SERCA1a. Also includes Na+/K+ and H+/K+ ATPases. -> Type IIA and IIB transports Ca2+. -> Type IIC contains Na+/K+ and H+/K+ ATPases from animal cells. -> Type IID contains few fungal ATPases of unknown function.
•Type III—Includes plasma membrane H+-ATPases from plants and fungi and Mg2+-ATPases from three bacterial species
•Type IV—Includes ATPases have been shown to be involved in the transport of phospholipids.
•Type V—ATPases with unknown specificity. This large group are only found in eukaryotes and are believed to be involved in cation transport in the endoplasmic reticulum.