Synapses
Nassir H. Sabah in Neuromuscular Fundamentals, 2020
The phosphate group is hydrolyzed back to an OH– group by enzymes referred to as phosphatases, and the process is known as dephosphorylation. Protein phosphatase 1 (PP1) dephosphorylates a variety of proteins as well as K+ and Ca2+ channels, NMDA, and AMPA glutamate receptors. Protein phosphatase 2A (PP2A) also dephosphorylates a range of proteins that overlap with those of PP1, in addition to tau protein that stabilizes microtubules of the cytoskeleton. Excessive phosphorylation of tau protein is associated with Alzheimer’s disease. Protein phosphatase 2B (PP2B), also known as calcineurin, is abundant in neurons and is activated by Ca2+. It activates T cells of the immune system and dephosphorylates AMPA receptors. Protein phosphorylation and dephosphorylation are of fundamental importance in cell functioning as it is the major molecular mechanism through which protein activity in a cell is regulated both in and outside the nervous system.
Apoptosis: Cellular Signaling and Molecular Mechanisms
John J. Lemasters, Constance Oliver in Cell Biology of Trauma, 2020
Additional evidence that phosphorylation of proteins is an important mechanism for regulation of apoptosis is derived from a variety of studies. Cells from a Burkitt’s lymphoma cell line (BM 13674) undergo apoptosis after induction of hyperthermia, following irradiation, or after treatment with a variety of compounds.40 This is associated with the dephosphorylation of several proteins. Furthermore, okadaic acid (an inhibitor of protein phosphatases 1 and 2A) protects these cells from programmed cell death.40 The effect elicited by okadaic acid is not blocked by treatment of these cells with protein synthesis inhibitors, phorbol esters, or by depletion of extracellular Ca2+. Hyperthermia and irradiation also cause apoptosis in CEM-C7 lymphocytes.41 Several proteins in these cells are dephosphorylated concurrently with the onset of apoptosis, and one appears identical to a dephosphorylated protein from apoptotic BM 13674 cells. Incubation of either cell type with okadaic acid inhibited apoptosis and the dephosphorylation of this common protein, which has a molecular mass of 40 kDa and an isoelectric point of 5.7. These data suggest that dephosphorylation of proteins common among some cells is required for onset of apoptosis. Which kinases are responsible for phosphorylation of these proteins remains unknown.
JAK-STAT pathway: Testicular development, spermatogenesis and fertility
Rajender Singh in Molecular Signaling in Spermatogenesis and Male Infertility, 2019
For fine-tuning of the pathway, there are positive and negative regulators that exist in the vertebrate and invertebrate systems. Positive regulation involves the ligand molecules (15), and negative regulation involves three basic mechanisms: dephosphorylation by protein tyrosine phosphatase (PTPs), STAT inhibition by protein inhibitors of activated STAT (PIAS) and negative feedback by suppressors of the cytokine signaling (SOCS) (14). As tyrosine phosphorylation is a central event in the pathway and activates the major players such as JAK and STAT, dephosphorylation of these positive regulators will have a negative effect on the pathway. The enzymes that are involved in dephosphorylation are called phosphatases. In mammals, the known tyrosine phosphatases are SHP1 (SH2 domain containing phosphatase), SHP2, protein tyrosine phosphatase B1 (PTPB1) and T-cell protein tyrosine phosphatase (TC-PTPs) (31). PIAS, as the name suggests, are the inhibitors of phosphorylated STAT. They constitute an E3 sumo ligase family and have four members present in mammals: PIAS1, PIASx, PIAS3 and PIASy (32). SOCS proteins suppress the JAK-STAT signaling pathway and generate a negative feedback loop in both mammals and Drosophila (33).
PTPN22: structure, function, and developments in inhibitor discovery with applications for immunotherapy
Published in Expert Opinion on Drug Discovery, 2022
Brenson A. Jassim, Jianping Lin, Zhong-Yin Zhang
The mechanism of PTPN22 catalyzed dephosphorylation hinges on catalytic C227, which exists as a thiolate anion (pKa ~ 5) within the active site microenvironment [2]. Upon substrate binding to the P-loop, this nucleophilic cysteine attacks the phosphate group, initiating the dephosphorylation process. Phosphate group cleavage is paired with protonation of the substrate tyrosyl leaving group by the general acid D195. Hydrolysis of the phospho-enzyme intermediate is facilitated by Q274, which coordinates a water molecule near the phospho-enzyme intermediate. Activation of water by the now general base D195 regenerates free enzyme. Mutation of residues C227 and D195 produces catalytically dead enzyme incapable of turning over substrate and has been utilized as a substrate-trapping mutant [16]. The C-terminal region of PTPN22 harbors four poly-proline motifs (P1-P4) (Figure 1(a)), of which P1 has been shown to bind Csk, an important enzyme in T-cell signaling [12,17–19]. One mutational study suggested this interdomain region inhibits enzymatic activity via intramolecular interaction between the catalytic and interdomain regions [20]. Phosphorylation of PTPN22 S35 by protein kinase C (PKC) abolishes Lck Y394 dephosphorylation inside Jurkat cells by altering conformation of the specific insert [13]. Furthermore, PTPN22 may be regulated by reversible oxidation as one crystal structure shows presence of a disulfide bond between catalytic C227 and C129 [15].
Recent developments in Phos-tag electrophoresis for the analysis of phosphoproteins in proteomics
Published in Expert Review of Proteomics, 2022
Hisashi Hirano, Jun Shirakawa
Kimura et al. [82] proposed two methods to distinguish between phosphorylated and non-phosphorylated proteins. (i) A method of dephosphorylation using alkaline phosphatase that does not lose its enzyme activity even in an SDS-containing buffer solution before electrophoresis. (ii) A method in which both the protein sample and ethylenediaminetetraacetic acid solutions were added into one well and only the sample solution was added into another well of the Phos-tag SDS-PAGE gel to investigate the change in mobility. However, neither of them consistently gave good results. Okawara et al. [23] thought that 2-DE combining SDS-PAGE and Phos-tag SDS-PAGE, which Kinoshita et al. [14] first used, could solve the abovementioned problem. Subsequently, Okawara et al. improved the 2-DE method and developed Phos-tag diagonal electrophoresis by which phosphorylated and non-phosphorylated proteins can be distinguished clearly.
Systems biomarker characteristics of circulating alkaline phosphatase activities for 48 types of human diseases
Published in Current Medical Research and Opinion, 2022
Wenhao Su, Tong Qiu, Meng Zhang, Cui Hao, Pengjiao Zeng, Zhangfeng Huang, Wenxing Du, Tianxiang Yun, Yunpeng Xuan, Lijuan Zhang, Yachong Guo, Wenjie Jiao
The biomolecular building blocks for both prokaryotes and eukaryotes include 20 amino acids for making proteins, eight nucleosides for replicating deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), 32 monosaccharides for assembling glycans, and eight lipids for constructing cellular membranes6. Most importantly, phosphorylation and dephosphorylation act on all biomolecules at both monomer and polymer levels and play critical roles in all aspects of biological processes7–13. ALP is a dephosphorylating enzyme discovered in the 1920s and a potential circulating biomarker in many human disorders14. More than 80% alkaline phosphatase in serum is released from the liver and bone and small amounts from the intestine15. It has been demonstrated that the circulating albumin to ALP ratio is related to the prognosis of various cancers16, which makes ALP a sound systems biomarker candidate.
Related Knowledge Centers
- Adenosine Diphosphate
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- Hydrolysis
- Organic Compound
- Phosphate
- Phosphorylation
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