SERCA - Sarco/Endoplasmic Reticulum Calcium-ATPase
P-type ATPase (P-ATPase) Superfamily
P-type ATPases can be divided into five subfamilies (types)
Type I consists of the transition/heavy metal ATPases.
Type II ATPases (specific for Na+,K+, H+ Ca2+, Mg2+ and phospholipids) predominate in eukaryotes. SERCA and Na+/K+ ATPases are member of this group.
There are 3 major paralogs, SERCA1-3, which are expressed at various levels in different cell types: SERCA1 - SERCA3, encoded by the genes ATP2A1 - ATP2A3.
Type III ATPases contains the plasma membrane H+-ATPases from plants and fungi.
Type IV ATPases have been shown to be involved in the transport of phospholipids
Type V ATPases have unknown specificity.
Many of these protein complexes are multisubunit with a large subunit serving the primary ATPase and ion translocation functions. Many eukaryotic P-type ATPases are monomeric or homodimeric enzymes of the catalytic subunit that hydrolyzes ATP. They contain the aspartyl phosphorylation site and catalyzes ion transport. The Na+/K+-ATPases, the Ca2+-ATPases and the (fungal) H+-ATPases of higher organisms exhibit 10 transmembrane α helical spanners (TMSs).
P-type ATPases are α-helical bundle primary transporters named based upon their ability to catalyze auto- (or self-) phosphorylation of a key conserved aspartate residue within the pump and their energy source, adenosine triphosphate (ATP). Most members of this transporter superfamily catalyze cation uptake and/or efflux, however one subfamily is involved in flipping phospholipids to maintain the asymmetric nature of the biomembrane.