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residuePhosphorylation is the addition of a phosphate (PO4) group to a protein molecule or a small molecule. Another way to define it would be the introduction of a phosphate group into an organic molecule. Its prominent role in biochemistry is the subject of a very large body of research (as of January 2006, the Medline database returns over 120,000 articles on the subject, largely on protein phosphorylation).

Protein phosphorylation History In 1906, Phoebus A. Levene at the Rockefeller Institute for Medical Research identified phosphate in the protein Vitellin (phosvitin), and by 1933 had detected phosphoserine in Casein, with Fritz Lipmann. However, it took another 20 years before Eugene P. Kennedy described the first ‘enzymatic phosphorylation of proteins’.

Function Reversible phosphorylation of proteins is an important regulatory mechanism which occurs in both Prokaryote and Eukaryote organisms.A.J. Cozzon (1988) Protein phosphorylation in prokaryotes Ann. Rev. Microbiol. 42:97-125 J.B. Stock, A.J. Ninfa and A.M. Stock (1989) Protein phosphorylation and regulation of adaptive responses in bacteria. Microbiol. Rev., p. 450-490 C. Chang and R.C. Stewart (1998) The Two-Component System. Plant Physiol. 117: 723-731D. Barford, A.K. Das and MP. Egloff. (1998) The Structure and mechanism of protein phosphatases: Insights into Catalysis and Regulation Annu Rev Biophys Biomol Struct. Vol. 27: 133-164 Enzymes called protein kinases (phosphorylation) and phosphatases (dephosphorylation) are involved in this process. Many enzymes and receptors are switched "on" or "off" by phosphorylation and dephosphorylation. Reversibe phosphorylation results in a Protein structure in the structure in many enzymes and receptors, causing them to become activated or deactivated. Phosphorylation usually occurs on serine, threonine, and tyrosine residues in eukaryotic proteins and where as it occurs on the basic amino acid residues histidine or arginine or lysine in prokaryotic proteins as well as on serine, threonine, and tyrosine residues. The addition of a phosphate (PO4) molecule to a polar R group of an amino acid residue can turn a hydrophobic portion of a protein into a polar and extremely hydrophilic portion of molecule. In this way it can introduce a conformational change in the structure of the protein via interaction with other hydrophobic and hydrophilic residues in the protein.

Once such example of the regulatory role that phosphorylation plays is the P53 (protein). The p53 protein is heavily regulated M. Ashcroft, M.H.G. Kubbutat, and K.H. Vousden (1999). Regulation of p53 Function and Stability by Phosphorylation. Mol Cell Biol Mar;19(3):1751-8. and contains more than 18 different phosphorylation sites. Activation of p53 can lead to cell cycle arrest, which can be reversed under some circumstances, or apoptotic cell death S. Bates, and K. H. Vousden. (1996). p53 in signalling checkpoint arrest or apoptosis. Curr. Opin. Genet. Dev. 6:1-7. This activity only occurs in situations where the cell is damaged or physiology is disturbed in normal healthy individuals.

Upon the deactivating signal, the protein becomes dephosphorylated again and stops working. This is the mechanism in many forms of signal transduction, for example the way in which incoming light is processed in the light-sensitive cells of the retina.

Regulatory roles of phosphorylation include

• Biological thermodynamics of energy-requiring reactions
• Phosphorylation of Na+/K+-ATPase during the transport of sodium (Na+) and potassium(K+) ions across the cell membrane in osmoregulation to maintain homeostasis#Biological homeostasis of the body's water content.

• Mediates enzyme Enzyme Inhibitor
• phosphorylation of the enzyme GSK-3 by AKT (Protein kinase B) as part of the insulin signaling pathway.P.C. van Weeren, K.M. de Bruyn, A.M. de Vries-Smits, J. Van Lint, B.M. Burgering. (1998). "Essential role for protein kinase B (PKB) in insulin-induced glycogen synthase kinase 3 inactivation. Characterization of dominant-negative mutant of PKB. J Biol Chem 22;273(21):13150-6.
• phosphorylation of Src (gene) tyrosine kinase (pronounced "sarc") by C-terminal Src kinase (Csk) induces a conformational change in the enzyme resulting in a fold in the structure which masks its kinase domain, and is thus shut "off".Cole, P.A., Shen, K., Qiao, Y., and Wang, D. (2003) Protein tyrosine kinases Src and Csk: A tail's tale, Curr. Opin. Chem., Biol. 7:580-585.

• Important for protein-protein interaction via "recognition protein domain".
• Phosphorylation of the cytosolic components of NADPH oxidase a large membrane bound, multi-protein enzyme present in phagocyte plays an important role in the regulation of protein-protein interactions in the enzyme.Babior, B.M., (1999). NADPH oxidase: an update. Blood 93, pp. 1464–1476

• Important in protein degredation.
• In the late 1990s it was recognized that phosphorylation of some proteins causes them to be degraded by the ATP-dependent ubiquitin/proteasome pathway. These target proteins become substrates for particular E3 ubiquitin ligases only when they are phosphorylated.

Signaling networks The network underlying phosphorylation can be very complex. In some cellular signalling, a protein A phosphorylates B, and B phosphorylates C, but A also phosphorylates C directly, and B can phosphorylate D, which may in turn phosphorylate A. Global approaches to identify and quantify phosphorylated proteins, like mass spectrometry-based proteomics, are becoming increasingly important for the systematic analysis of complex phosphorylation networks. For example, one study has identified dynamic changes in the phosphorylation status of more than 6000 sites after stimulation with epidermal growth factor. Analysis of phosphoproteins is a branch of proteomics called phosphoproteomics.

Protein phosphorylation sites There are thousands of distinct phosphorylation sites in a given cell since:1) There are thousands of different kinds of proteins in any particular cell (such as a lymphocyte).2) It is estimated that 1/10th to 1/2 of proteins are phosphorylated (in some cellular state).3) Phosphorylation often occurs on multiple distinct sites on a given protein.

Since phosphorylation of any site on a given protein can change the function or localization of that protein, understanding the "state" of a cell requires knowing the phosphorylation state of its proteins. For example, if amino acid Serine-473 ("S473") in the protein AKT is phosphorylated AKT is generally functionally active as a kinase. If not, it is an inactive kinase.

Types of phosphorylation See also kinases for more details on the different types of phosphorylation

Within a protein, phosphorylation can occur on several amino acids. Phosphorylation on serine is the most common, followed by threonine. Tyrosine phosphorylation is relatively rare. However, since tyrosine phosphorylated proteins are relatively easy to purify using antibodies, tyrosine phosphorylation sites are relatively well understood. Histidine and aspartate phosphorylation occurs in prokaryotes as part of two-component signalling.

Detection and characterization Antibodies can be used as powerful tools to detect whether a protein is phosphorylated at any particular site. Such antibodies are called phospho-specific antibodies; hundreds of such antibodies are now available. They are becoming critical reagents both for basic research and for clinical diagnosis.

PTM (Phospho-Tyrosine Modified) isoforms are easily detected on Two-dimensional gel electrophoresis. Indeed, phosphorylation replaces neutral hydroxyl groups on serines, threonines or tyrosines with negatively charged phosphates with pKs near 1.2 and 6.5. Thus, below pH 5.5, phosphates add a single negative charge, near pH 6.5 they add 1.5 negative charges and above pH 7.5 they add 2 negative charges. The relative amount of each isoform can also easily and rapidly be determined from staining intensity on 2D gels.

A detailed characterization of the sites of phosphorylation is very difficult and the quantitation of protein phosphorylation by mass spectrometry requires isotopic internal standard approaches ( Gerber et al., 2003). A relative quantitation can be obtained with a variety of differential isotope labeling technologies ( Gigy et al., 2002, Goshe et al., 2003).

Other kinds adenosine triphosphate, the "high-energy" exchange medium in the cell, is synthesized in the mitochondrion by addition of a third phosphate group to Adenosine diphosphate in a process referred to as oxidative phosphorylation. ATP is also synthesized by substrate-level phosphorylation during glycolysis.ATP is synthesized at the expense of solar energy by photophosphorylation in the chloroplasts of plant cells.

Phosphorylation of sugars is often the first stage of their catabolism. It allows cells to accumulate sugars because the phosphate group prevents the molecules from diffusing back across their transporter.

External links

• Mammalian Phosphorylation Resource, which integrates information on available phospho-specific antibodies
• deltaMasses detection and localization of phosphorylations after mass spectrometry
• Functional analyses for site-specific phosphorylation of a target protein in cells (A Protocol)

References

residuePhosphorylation is the addition of a phosphate (PO4) group to a protein molecule or a small molecule. Another way to define it would be the introduction of a phosphate group into an organic molecule. Its prominent role in biochemistry is the subject of a very large body of research (as of January 2006, the Medline database returns over 120,000 articles on the subject, largely on protein phosphorylation).

Protein phosphorylation History In 1906, Phoebus A. Levene at the Rockefeller Institute for Medical Research identified phosphate in the protein Vitellin (phosvitin), and by 1933 had detected phosphoserine in Casein, with Fritz Lipmann. However, it took another 20 years before Eugene P. Kennedy described the first ‘enzymatic phosphorylation of proteins’.

Function Reversible phosphorylation of proteins is an important regulatory mechanism which occurs in both Prokaryote and Eukaryote organisms.A.J. Cozzon (1988) Protein phosphorylation in prokaryotes Ann. Rev. Microbiol. 42:97-125 J.B. Stock, A.J. Ninfa and A.M. Stock (1989) Protein phosphorylation and regulation of adaptive responses in bacteria. Microbiol. Rev., p. 450-490 C. Chang and R.C. Stewart (1998) The Two-Component System. Plant Physiol. 117: 723-731D. Barford, A.K. Das and MP. Egloff. (1998) The Structure and mechanism of protein phosphatases: Insights into Catalysis and Regulation Annu Rev Biophys Biomol Struct. Vol. 27: 133-164 Enzymes called protein kinases (phosphorylation) and phosphatases (dephosphorylation) are involved in this process. Many enzymes and receptors are switched "on" or "off" by phosphorylation and dephosphorylation. Reversibe phosphorylation results in a Protein structure in the structure in many enzymes and receptors, causing them to become activated or deactivated. Phosphorylation usually occurs on serine, threonine, and tyrosine residues in eukaryotic proteins and where as it occurs on the basic amino acid residues histidine or arginine or lysine in prokaryotic proteins as well as on serine, threonine, and tyrosine residues. The addition of a phosphate (PO4) molecule to a polar R group of an amino acid residue can turn a hydrophobic portion of a protein into a polar and extremely hydrophilic portion of molecule. In this way it can introduce a conformational change in the structure of the protein via interaction with other hydrophobic and hydrophilic residues in the protein.

Once such example of the regulatory role that phosphorylation plays is the P53 (protein). The p53 protein is heavily regulated M. Ashcroft, M.H.G. Kubbutat, and K.H. Vousden (1999). Regulation of p53 Function and Stability by Phosphorylation. Mol Cell Biol Mar;19(3):1751-8. and contains more than 18 different phosphorylation sites. Activation of p53 can lead to cell cycle arrest, which can be reversed under some circumstances, or apoptotic cell death S. Bates, and K. H. Vousden. (1996). p53 in signalling checkpoint arrest or apoptosis. Curr. Opin. Genet. Dev. 6:1-7. This activity only occurs in situations where the cell is damaged or physiology is disturbed in normal healthy individuals.

Upon the deactivating signal, the protein becomes dephosphorylated again and stops working. This is the mechanism in many forms of signal transduction, for example the way in which incoming light is processed in the light-sensitive cells of the retina.

Regulatory roles of phosphorylation include

• Biological thermodynamics of energy-requiring reactions
• Phosphorylation of Na+/K+-ATPase during the transport of sodium (Na+) and potassium(K+) ions across the cell membrane in osmoregulation to maintain homeostasis#Biological homeostasis of the body's water content.

• Mediates enzyme Enzyme Inhibitor
• phosphorylation of the enzyme GSK-3 by AKT (Protein kinase B) as part of the insulin signaling pathway.P.C. van Weeren, K.M. de Bruyn, A.M. de Vries-Smits, J. Van Lint, B.M. Burgering. (1998). "Essential role for protein kinase B (PKB) in insulin-induced glycogen synthase kinase 3 inactivation. Characterization of dominant-negative mutant of PKB. J Biol Chem 22;273(21):13150-6.
• phosphorylation of Src (gene) tyrosine kinase (pronounced "sarc") by C-terminal Src kinase (Csk) induces a conformational change in the enzyme resulting in a fold in the structure which masks its kinase domain, and is thus shut "off".Cole, P.A., Shen, K., Qiao, Y., and Wang, D. (2003) Protein tyrosine kinases Src and Csk: A tail's tale, Curr. Opin. Chem., Biol. 7:580-585.

• Important for protein-protein interaction via "recognition protein domain".
• Phosphorylation of the cytosolic components of NADPH oxidase a large membrane bound, multi-protein enzyme present in phagocyte plays an important role in the regulation of protein-protein interactions in the enzyme.Babior, B.M., (1999). NADPH oxidase: an update. Blood 93, pp. 1464–1476

• Important in protein degredation.
• In the late 1990s it was recognized that phosphorylation of some proteins causes them to be degraded by the ATP-dependent ubiquitin/proteasome pathway. These target proteins become substrates for particular E3 ubiquitin ligases only when they are phosphorylated.

Signaling networks The network underlying phosphorylation can be very complex. In some cellular signalling, a protein A phosphorylates B, and B phosphorylates C, but A also phosphorylates C directly, and B can phosphorylate D, which may in turn phosphorylate A. Global approaches to identify and quantify phosphorylated proteins, like mass spectrometry-based proteomics, are becoming increasingly important for the systematic analysis of complex phosphorylation networks. For example, one study has identified dynamic changes in the phosphorylation status of more than 6000 sites after stimulation with epidermal growth factor. Analysis of phosphoproteins is a branch of proteomics called phosphoproteomics.

Protein phosphorylation sites There are thousands of distinct phosphorylation sites in a given cell since:1) There are thousands of different kinds of proteins in any particular cell (such as a lymphocyte).2) It is estimated that 1/10th to 1/2 of proteins are phosphorylated (in some cellular state).3) Phosphorylation often occurs on multiple distinct sites on a given protein.

Since phosphorylation of any site on a given protein can change the function or localization of that protein, understanding the "state" of a cell requires knowing the phosphorylation state of its proteins. For example, if amino acid Serine-473 ("S473") in the protein AKT is phosphorylated AKT is generally functionally active as a kinase. If not, it is an inactive kinase.

Types of phosphorylation See also kinases for more details on the different types of phosphorylation

Within a protein, phosphorylation can occur on several amino acids. Phosphorylation on serine is the most common, followed by threonine. Tyrosine phosphorylation is relatively rare. However, since tyrosine phosphorylated proteins are relatively easy to purify using antibodies, tyrosine phosphorylation sites are relatively well understood. Histidine and aspartate phosphorylation occurs in prokaryotes as part of two-component signalling.

Detection and characterization Antibodies can be used as powerful tools to detect whether a protein is phosphorylated at any particular site. Such antibodies are called phospho-specific antibodies; hundreds of such antibodies are now available. They are becoming critical reagents both for basic research and for clinical diagnosis.

PTM (Phospho-Tyrosine Modified) isoforms are easily detected on Two-dimensional gel electrophoresis. Indeed, phosphorylation replaces neutral hydroxyl groups on serines, threonines or tyrosines with negatively charged phosphates with pKs near 1.2 and 6.5. Thus, below pH 5.5, phosphates add a single negative charge, near pH 6.5 they add 1.5 negative charges and above pH 7.5 they add 2 negative charges. The relative amount of each isoform can also easily and rapidly be determined from staining intensity on 2D gels.

A detailed characterization of the sites of phosphorylation is very difficult and the quantitation of protein phosphorylation by mass spectrometry requires isotopic internal standard approaches ( Gerber et al., 2003). A relative quantitation can be obtained with a variety of differential isotope labeling technologies ( Gigy et al., 2002, Goshe et al., 2003).

Other kinds adenosine triphosphate, the "high-energy" exchange medium in the cell, is synthesized in the mitochondrion by addition of a third phosphate group to Adenosine diphosphate in a process referred to as oxidative phosphorylation. ATP is also synthesized by substrate-level phosphorylation during glycolysis.ATP is synthesized at the expense of solar energy by photophosphorylation in the chloroplasts of plant cells.

Phosphorylation of sugars is often the first stage of their catabolism. It allows cells to accumulate sugars because the phosphate group prevents the molecules from diffusing back across their transporter.

External links

• Mammalian Phosphorylation Resource, which integrates information on available phospho-specific antibodies
• deltaMasses detection and localization of phosphorylations after mass spectrometry
• Functional analyses for site-specific phosphorylation of a target protein in cells (A Protocol)

References

Phosphorylation - Wikipedia, the free encyclopedia
Phosphorylation is the addition of a phosphate (PO 4) group to a protein molecule or a small molecule. It can also be thought of as the introduction of a phosphate group into an ...

MRC Protein Phosphorylation Unit :: Home
14 July Former MRC Protein Phosphorylation Unit Postdoctoral Fellow sells biotechnology company for US $160... more.....

MRC Protein Phosphorylation Unit :: Studentships
An MRC funded Capacity Building PhD Studentship with Dario Alessi available (start date October 2008). The projects for the 2009 MRC Protein Phosphorylation Unit PhD Prize ...

Definition: phosphorylation from Online Medical Dictionary
The Online Medical Dictionary is a searchable dictionary of definitions from medicine, science and technology.

GO:0016310 phosphorylation - QuickGO
The European Bioinformatics Institute ... You can reach the search box using alt+9 (Win/IE), alt+shift+9 (Win/Firefox) or ctrl+9 (Mac)

GO:0006468 protein amino acid phosphorylation - QuickGO
The European Bioinformatics Institute ... You can reach the search box using alt+9 (Win/IE), alt+shift+9 (Win/Firefox) or ctrl+9 (Mac)

Bioenergetics
Oxidative Phosphorylation Home Page. These pages describe how mitochondria use the energy from substrate oxidation to ...

Bioenergetics
2) Phosphorylation inhibitors (e.g. oligomycin) abolish the burst of oxygen consumption after adding ADP, but have no effect on uncoupler-stimulated respiration.

Medical Research Council Protein Phosphorylation Unit
MRC Protein Phosphorylation Unit The MRC Protein Phosphorylation Unit is located in the Sir James Black Centre.

Reversible Proteins Phosphorylation
Reversible Proteins Phosphorylation. Barford Group. Section: Section of Structural Biology. Reversible protein phosphorylation is a ubiquitous mechanism for the control of signal ...