Phosphatases

A phosphatase is an enzyme that uses water to cleave a phosphoric acid monoester into a phosphate ion and an alcohol. Because a phosphatase enzyme catalyzes the hydrolysis of its substrate, it is a subcategory of hydrolases. Phosphatase enzymes are essential to many biological functions, because phosphorylation (e.g. by protein kinases) and dephosphorylation (by phosphatases) serve diverse roles in cellular regulation and signaling. Whereas phosphatases remove phosphate groups from molecules, kinases catalyze the transfer of phosphate groups to molecules from ATP. Together, kinases and phosphatases direct a form of post-translational modification that is essential to the cell's regulatory network. Phosphatase enzymes are not to be confused with phosphorylase enzymes, which catalyze the transfer of a phosphate group from hydrogen phosphate to an acceptor. Due to their prevalence in cellular regulation, phosphatases are an area of interest for pharmaceutical research.

Phosphatases catalyze the hydrolysis of a phosphomonoester, removing a phosphate moiety from the substrate. Water is split in the reaction, with the -OH group attaching to the phosphate ion, and the H+ protonating the hydroxyl group of the other product. The net result of the reaction is the destruction of a phosphomonoester and the creation of both a phosphate ion and a molecule with a free hydroxyl group.

Phosphatases are able to dephosphorylate seemingly different sites on their substrates with great specificity. Identifying the "phosphatase code," that is, the mechanisms and rules that govern substrate recognition for phosphatases, is still a work in progress, but the first comparative analysis of all the protein phosphatases encoded across nine eucaryotic 'phosphatome' genomes is now available. Studies reveal that so called "docking interactions" play a significant role in substrate binding. A phosphatase recognizes and interacts with various motifs (elements of secondary structure) on its substrate; these motifs bind with low affinity to docking sites on the phosphatase, which are not contained within its active site. Although each individual docking interaction is weak, many interactions occur simultaneously, conferring a cumulative effect on binding specificity. Docking interactions can also allosterically regulate phosphatases and thus influence their catalytic activity.

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