WHAT ARE PHOSPHOPROTEINS? - BIOLOGY - 2024

The phosphoproteins are proteins which are joined by a covalent bond to a phosphate group. This union happens by modifications that occur after DNA translation.

There are phosphoproteins whose bonding to phosphate groups is common, as in the case of casein and valetine.

3D structure of casein, a phosphoprotein

However, there are many other proteins that during cellular processes are temporarily phosphorylated by regulatory mechanisms and become phosphoproteins.

Phosphoproteins are usually attached to phosphate groups at specific amino acids in their sequences. The amino acids that are commonly associated with phosphate groups are serine, threonine, tyrosine, histidine, and aspartic acid.

Phosphoproteins are involved in important activities of the cellular process. Among them are: the protection of structures of cells and organisms, the regulation of cellular processes, signaling and adaptation to new environmental conditions.

Importance of phosphoproteins

Adaptive processes in different organisms, especially bacteria, are closely linked to phosphoproteins.

In many cases, the cellular mechanisms that allow a cell to adapt to environmental conditions are controlled by the generation of phosphoproteins.

The addition of phosphate groups to proteins generating phosphoproteins can inhibit the binding of ligands and receptors. In this way, phosphoproteins play an essential role in the regulation of cellular activity.

Phosphoproteins have been used in the clinical industry as important biomarkers to identify some types of cancer, especially breast cancer.

Furthermore, casein, a well-studied phosphoprotein, is important in the dairy industry.

Protein phosphorylation process in cell regulation

In the processes of regulation of cell activity, phosphorylation occurs mainly by the action of 2 types of enzymatic components.

One is the histidine protein kinases, known as HPK, and the other is the response regulators, which are the proteins to be regulated through phosphorylation.

During regulation and also in some cases of cell signaling, there is a transfer of phosphate groups from an ATP (adenosine triphosphate) molecule to the histidine residues of HPKs.

This phosphate group then passes to an aspartic acid residue in the response regulators and is finally released into the water.

Casein and yolk

Although many proteins can be temporarily phosphorylated by the cell's regulatory system, creating a large number of phosphoproteins, casein and vitellin are specific cases of phosphoproteins constantly attached to phosphate groups.

Casein is a protein found mainly in products like milk. This phosphoprotein is known as the insoluble protein in milk.

There are several species of casein whose particularities and properties can give different characteristics to dairy products.

Vitellin is the main protein in the yolk of eggs. This protein separates the white from the yolk and protects it from possible breakage.

This phosphoprotein has a close relationship to lipoproteins in egg yolk. These lipoproteins are lipovitelenin and lipovitellin.

References

1. Back JF et al. Proteins of the outer layer of the vitelline membrane of hen's eggs. Biochimica et biophysica acta. 1982; 705 (1): 12-19
2. Blom N. Gammeltoft S. Brunak S. Sequence and structure-based prediction of eukaryotic protein phosphorylation sites. Journal of Molecular Biology. 1999; 294 (5): 1351-1362
3. Ptacek J. Mah AS Global analysis of protein phosphorylation in yeast. Nature. 2005; 438 (7068): 679-684
4. Stock J. Nymph A. Stock A. Protein phosphorylation and regulation of adaptive responses in bacteria. Microbiology and molecular biology reviews. 1989; 53 (4): 450-490
5. Weller M. (1979). Protein phosphorilation. Pion Ltd. London, Uk
6. Zittle C. Custer J. Purification and some properties of α _s -Casein and κ -Casein. Journal of Dairy Science. 1963; 46 (11): 1183-1188.