The P-type superfamily of ion pumps includes primary transporters energized by hydrolysis of ATP with a wide range of specificities for small cations and perhaps also phospholipids (Møller et al., 1996; Palmgren and Harper, 1999). P-type ATPases are characterized by forming a phosphorylated intermediate (hence the name P-type)
The most prominent subfamilies are P1B ATPases (heavy metal pumps; seven members), P2A and P2B ATPases (Ca2+ pumps; 14 in total), P3A ATPases (plasma membrane H+ pumps; 12 members including a truncated pump, which might represent a pseudogene or an ATPase-like protein with an alternative function), and P4 ATPases (12 members). P4 ATPases have been implicated in aminophosholipid flipping but it is not known whether this is a direct or an indirect effect of pump activity
The P-type ATPases, also known as E1-E2 ATPases, are a large group of evolutionarily related ion pumps that are found in bacteria, archaea and eukaryotes. They are α-helical bundle primary transporters refereed to as P-type ATPases because they catalyze auto- (or self) phosphorylation of a key conserved aspartate residue within the pump. In addition, they all appear to interconvert between at least two different conformations, denoted by E1 and E2.
Most members of this transporter family are specific for the pumping of a large array of cations, however one subfamily is involved in flipping phospholipids to maintain the asymmetric nature of the biomembrane.
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).
diversification of the P-type ATPase family occurred prior to the separation of eubacteria, archaea and eucaryota. This underlines the significance of this protein family for cell survival.
* Type I consists of the transition/heavy metal ATPases.
o Type IA ATPases are involved in K+ import.
Type IB ATPases are involved in transport of the soft Lewis acids: Cu+, Ag+, Cu2+, Zn2+, Cd2+, Pb2+ and Co2+
* Type II ATPases are split into four groups.
o Type IIA transports Ca2+. SERCA1a is a type IIA pump.
o Type IIB transports Ca2+.
o Type IIC consists of the closely related Na+/K+ and H+/K+ ATPases from animal cells.
o Type IID contains a small number of fungal ATPases of unknown function.
* Type III ATPases contains the plasma membrane H+-ATPases from plants and fungi (IIIA) and a small subdivision with Mg2+-ATPases from three bacterial species (IIIB).
* Type IV ATPases have been shown to be involved in the transport of phospholipids. However the transport specificity of the P-IV type ATPases still remains a somewhat controversial subject.
* Type V ATPases have unknown specificity. This large group are only found in eukaryotes and are believed to be involved in cation transport in the endoplasmic reticulum.