Phosphorylation

To phosphorylate is understood in biochemistry, the reversible ( invertible ) of a phosphate group to an organic molecule, in particular to proteins. The results are phosphoproteins. This phosphorylation is ( in addition to the allosteric and competitive inhibition ), the regulation of biological processes important in the cell dar. Chemical, is the formation of a phosphoric acid ester.

Phosphorylation of proteins

In the process involved enzymes

The enzymes which catalyze the phosphorylation of proteins, called protein kinases. Here, a phosphate group covalently linked to an amino acid residue, typically with ATP as a substrate for the phosphate. Another enzyme category that phosphatases can reverse this process, ie the phosphate group is removed from the protein. Protein kinases and phosphatases are very specific in the rule and can also be controlled specifically in their activity.

Function

As a phosphate group has a polar charge, phosphorylation often has conformational changes of the protein sequence, so that there are two forms of the protein may be functionally different depending on whether it is phosphorylated or not. These two forms, depending on the individual case, which represent activated or inactivated forms of a protein. Many transcription factors are activated in this way via signal transduction cascades, such as CREB.

Another form of influence by phosphorylation is the regulation of protein binding sites. Particular protein domains that mediate these interactions are phosphorylated and can no longer form protein complexes. Many receptors, such as G -protein coupled receptors, can be regulated in this way in their activity. Protein phosphorylation and dephosphorylation thus have regulatory function.

Site of phosphorylation

Three amino acids in proteins are mostly phosphorylated, namely those having a hydroxy group in the side chain: tyrosine kinases, bind the phosphate group of tyrosine, serine / threonine kinases to serine or threonine. In this case, serine is the most common phosphorylated amino acid. The ratio of the phosphorylation of Ser, Thr and Tyr is 1800: 200: 1

Even rarer than tyrosine, the amino acids histidine, arginine, lysine, cysteine, glutamate and aspartate are phosphorylated. However, there are also these phosphorylations Examples: The phosphotransferase system ( PTS) are phosphorylated several histidines and a cysteine. For two component systems that are involved in signal transduction, conserved histidine or aspartate residues are phosphorylated.

Phosphorylation of other molecules

, Other molecules ( sugar nucleotides) phosphorylated, this generally serves to provide chemical energy in the molecule to endothermic in subsequent steps, that to enable energy-consuming conversions. Polyphosphates such as ATP or creatine phosphate used in metabolism as a universal " energy currency " for the intermediate storage and exchange of energy between different processes.