Inositol hexakisphosphate, often called phytate, is found in abundance in seeds and acting as an inorganic phosphate reservoir. Phytases are phosphatases that hydrolyze phytate to less-phosphorylated myo-inositol derivatives and inorganic phosphate. The active-site sequence (HCXXGXGR) of the phytase identified from the gut micro-organism Selenomonas ruminantium forms a loop (P loop) at the base of a substrate binding pocket that is characteristic of protein tyrosine phosphatases (PTPs). The depth of this pocket is an important determinant of the substrate specificity of PTPs. In humans this enzyme is thought to aid bone mineralization and salvage the inositol moiety prior to apoptosis PMID:9923613.
Family alignment:
There are 2612 PTPlike_phytase domains in 1487 proteins in SMART's nrdb database.
Click on the following links for more information.
Evolution (species in which this domain is found)
Taxonomic distribution of proteins containing PTPlike_phytase domain.
This tree includes only several representative species. The complete taxonomic breakdown of all proteins with PTPlike_phytase domain is also avaliable.
Click on the protein counts, or double click on taxonomic names to display all proteins containing PTPlike_phytase domain in the selected taxonomic class.
Literature (relevant references for this domain)
Primary literature is listed below; Automatically-derived, secondary literature is also avaliable.
Effect of ionic strength and oxidation on the P-loop conformation of the protein tyrosine phosphatase-like phytase, PhyAsr.
FEBS J. 2008; 275: 3783-92
Display abstract
The protein tyrosine phosphatase (PTP)-like phytase, PhyAsr, from Selenomonasruminantium is a novel member of the PTP superfamily, and the only describedmember that hydrolyzes myo-inositol-1,2,3,4,5,6-hexakisphosphate. In addition to the unique substrate specificity of PhyAsr, the phosphate-binding loop (P-loop)has been reported to undergo a conformational change from an open (inactive) to aclosed (active) conformation upon ligand binding at low ionic strength. At highionic strengths, the P-loop was observed in the closed, active conformation inboth the presence and absence of ligand. To test whether the P-loop movement can be induced by changes in ionic strength, we examined the effect that ionicstrength has on the catalytic efficiency of PhyAsr, and determined the structure of the enzyme at several ionic strengths. The catalytic efficiency of PhyAsr ishighly sensitive to ionic strength, with a seven-fold increase in k(cat)/K(m) anda ninefold decrease in K(m) when the ionic strength is increased from 100 to 500 mm. Surprisingly, the P-loop is observed in the catalytically competentconformation at all ionic strengths, despite the absence of a ligand. Here weprovide structural evidence that the ionic strength dependence of PhyAsr and the conformational change in the P-loop are not linked. Furthermore, we demonstratethat the previously reported P-loop conformational change is a result ofirreversible oxidation of the active site thiolate. Finally, we rationalize theobserved P-loop conformational changes observed in all oxidized PTP structures.
Structures of Selenomonas ruminantium phytase in complex with persulfatedphytate: DSP phytase fold and mechanism for sequential substrate hydrolysis.
Structure. 2004; 12: 2015-24
Display abstract
Various inositide phosphatases participate in the regulation of inositolpolyphosphate signaling molecules. Plant phytases are phosphatases that hydrolyzephytate to less-phosphorylated myo-inositol derivatives and phosphate. Thephytase from Selenomonas ruminantium shares no sequence homology with othermicrobial phytases. Its crystal structure revealed a phytase fold of thedual-specificity phosphatase type. The active site is located near a conservedcysteine-containing (Cys241) P loop. We also solved two other crystal forms inwhich an inhibitor, myo-inositol hexasulfate, is cocrystallized with the enzyme. In the "standby" and the "inhibited" crystal forms, the inhibitor is bound,respectively, in a pocket slightly away from Cys241 and at the substrate binding site where the phosphate group to be hydrolyzed is held close to the -SH group ofCys241. Our structural and mutagenesis studies allow us to visualize the way inwhich the P loop-containing phytase attracts and hydrolyzes the substrate(phytate) sequentially.
The human and rat forms of multiple inositol polyphosphate phosphatase:functional homology with a histidine acid phosphatase up-regulated duringendochondral ossification.
FEBS Lett. 1999; 442: 99-104
Display abstract
We have derived the full-length sequences of the human and rat forms of themultiple inositol polyphosphate phosphatase (MIPP); their structural andfunctional comparison with a chick histidine acid phosphatase (HiPER1) hasrevealed new information: (1) MIPP is approximately 50% identical to HiPER1, but the ER-targeting domains are divergent; (2) MIPP appears to share the catalyticrequirement of histidine acid phosphatases, namely, a C-terminal His residueremote from the RHGxRxP catalytic motif; (3) rat MIPP mRNA is up-regulated duringchondrocyte hypertrophy. The latter observation provides a context for proposing that MIPP may aid bone mineralization and salvage the inositol moiety prior toapoptosis.
