TIGR01494

ATPase, P-type (transporting), HAD superfamily, subfamily IC; The P-type ATPases are a large family of trans-membrane transporters acting on charged substances. The distinguishing feature of the family is the formation of a phosphorylated intermediate (aspartyl-phosphate) during the course of the reaction. Another common name for these enzymes is the E1-E2 ATPases based on the two isolable conformations: E1 (unphosphorylated) and E2 (phosphorylated). Generally, P-type ATPases consist of only a single subunit encompassing the ATPase and ion translocation pathway, however, in the case of the potassium (TIGR01497) and sodium/potassium (TIGR01106) varieties, these functions are split between two subunits. Additional small regulatory or stabilizing subunits may also exist in some forms. P-type ATPases are nearly ubiquitous in life and are found in numerous copies in higher organisms (at least 45 in Arabidopsis thaliana, for instance ). Phylogenetic analyses have revealed that the P-type ATPase subfamily is divided up into groups based on substrate specificities and this is represented in the various subfamily and equivalog models that have been made: IA (K+) TIGR01497, IB (heavy metals) TIGR01525, IIA1 (SERCA-type Ca++) TIGR01116, IIA2 (PMR1-type Ca++) TIGR01522, IIB (PMCA-type Ca++) TIGR01517, IIC (Na+/K+, H+/K+ antiporters) TIGR01106, IID (fungal-type Na+ and K+) TIGR01523, IIIA (H+) TIGR01647, IIIB (Mg++) TIGR01524, IV (phospholipid, flippase) TIGR01652 and V (unknown specificity) TIGR01657. The crystal structure of one calcium-pumping ATPase and an analysis of the fold of the catalytic domain of the P-type ATPases have been published. These reveal that the catalytic core of these enzymes is a haloacid dehalogenase(HAD)-type aspartate-nucleophile hydrolase. The location of the ATP-binding loop in between the first and second HAD conserved catalytic motifs defines these enzymes as members of subfamily I of the HAD superfamily (see also TIGR01493, TIGR01509, TIGR01549, TIGR01544 and TIGR01545). Based on these classifications, the P-type ATPase _superfamily_ corresponds to the IC subfamily of the HAD superfamily.