Phosphatase is an enzyme that removes a phosphate group from its substrate by hydrolyzing a phosphate monoester to a phosphate ion and a molecule having a free hydroxyl group. This effect is in contrast to the action of phosphorylases and kinases, which use a high-energy molecule such as ATP to attach a phosphate group to its substrate. The phosphatase common in many organisms is alkaline phosphatase. Another major class of proteins is found in archaea, bacteria and eukaryotes. Another group of phosphatases, collectively referred to as protein phosphatases, removes phosphate groups from phosphorylated amino acid residues of the substrate protein. Protein phosphorylation is a common post-translational modification of proteins catalyzed by protein kinases, and protein phosphatases reverse this effect. Protein phosphorylation can be found on tyrosine, serine and threonine residues. Phosphates can be removed from all of these residues or a subset thereof depending on the phosphatase selected. In particular, phosphatases have been characterized as being active against serine and threonine residues or against tyrosine residues. Protein phosphorylation mediates signal transduction during development, transcription, immune response, metabolism, apoptosis, and cell differentiation. Serine/threonine protein phosphatase or protein phosphatase 2, also known as PP2A or PP2, is an enzyme encoded by PPP2CA in humans. The PP2A heterotrimeric protein phosphatase is a ubiquitous and conserved serine/threonine phosphatase with broad substrate specificity and multiple cellular functions. The target of PP2A is a protein that is involved in the oncogenic signaling cascade, such as Raf and AKT. Lymphocyte activation must be tightly regulated to ensure adequate immunity to pathogens and prevent autoimmunity. Protein tyrosine phosphatases (PTPs) play a key role in this regulation by controlling the function of key receptors and intracellular signaling molecules in lymphocytes.
The protein serine/threonine phosphatase of the PPP family plays a variety of roles in mediating intracellular signaling. In addition to PP1, PP2A and PP2B, related novel protein phosphatases have recently been characterized, which occur in a low abundance and tissue and development specific manner. PP1 and PP2A are specifically inhibited by various naturally occurring toxins, such as okadaic acid, a diarrhea shellfish poison and a strong tumor promoter, and microcystins, a hepatotoxin produced by blue-green algae. Although PP2B is only difficult to inhibit by toxins affecting PP1 and PP2A, it has recently been defined as an immunosuppressive target of FK506 and cyclosporin, which are related to their major cell-binding protein, cis-trans-peptidyl-propyl. The constitutive enzyme FKBP12 and the cyclophilin are related, respectively. The structural complexity of the PP1 and PP2 holoenzymes in vivo solves the seemingly contradictory situation, that is, a relatively small amount of protein phosphatase catalytic subunit is responsible for the specific dephosphorylation of various cellular proteins, and both PP1 and PP2A are involved in regulation. Many different cellular functions include glycogen metabolism, muscle contraction, cell cycle control, and RNA splicing. Since the individual catalytic subunits of PP1 and PP2A catalyze the dephosphorylation of broad and overlapping substrates in vitro, in vivo specificity is produced by altering the selectivity of the enzyme for a particular substrate or by targeting the phosphatase to a subcellular location. Its substrate. This is achieved by regulation or targeting subunits that bind to the phosphatase catalytic subunit. In addition, regulatory subunits allow PPP activity to be regulated by reversible protein phosphorylation and second messenger.
The dephosphoiylation of proteins on their serine, threonine and tyrosine residues is catalyzed by three families of protein phosphatases that regulate numerous intracellular processes. Diversity of structure within a family is generated by targeting the regulatory subunits and domains. Structural studies of these enzymes have revealed that although two families of protein serine/threonine phosphatases are unrelated in sequence, the architecture of their catalytic domains is remarkably similar and distinct from the protein tyrosine phosphatases. Reversible protein phosphorylation is a critical component of the signal transduction mechanisms by which extracellular signals regulate homeostasis and cell growth. Extracellular effectors act by modulating protein kinases and protein phosphatases, which catalyze the opposing activities of protein phosphorylation and dephosphorylation, respectively. Change in the phosphorylation state of proteins on their serine, threonine and tyrosine residues are responsible for disparate protein confirmational and hence functional changes, and this, together with its reversibility and scope for signal amplification, probably accounts for the importance of protein phosphorylation in signal transduction.