Phosphorylation

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Phosphorylation is the addition of a phosphate (PO4) group to a protein or other organic molecule. Phosphorylation activates or deactivates many protein enzymes, causing or preventing the mechanisms of diseases such as cancer and diabetes.

Protein phosphorylation in particular plays a significant role in a wide range of cellular processes. Its prominent role in biochemistry is the subject of a very large body of research (as of March 2009, the Medline database returns nearly 160,000 articles on the subject, largely on protein phosphorylation).

Contents

Protein phosphorylation

History

In 1906, Phoebus A. Levene at the Rockefeller Institute for Medical Research identified phosphate in the protein vitellin (phosvitin),[1] and by 1933 had detected phosphoserine in casein, with Fritz Lipmann.[2] However, it took another 20 years before Eugene P. Kennedy described the first ‘enzymatic phosphorylation of proteins’.[3]

Function

Reversible phosphorylation of proteins is an important regulatory mechanism that occurs in both prokaryotic and eukaryotic organisms.[4][5][6][7] Enzymes called kinases (phosphorylation) and phosphatases (dephosphorylation) are involved in this process. Many enzymes and receptors are switched "on" or "off" by phosphorylation and dephosphorylation. Reversible phosphorylation results in a conformational change 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. In addition, phosphorylation occurs on the basic amino acid residues histidine or arginine or lysine in prokaryotic proteins.[4][5] 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.

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