Protein phosphorylation is the most basic, common, and important mechanism for regulating and controlling protein activity and function. Protein phosphorylation occurs mainly on two amino acids, one is serine (including threonine) and the other is tyrosine. These two types of acid phosphorylation enzymes are different and function differently, but there are also a few bifunctional enzymes that can act on both types of amino acids, such as MEK (mitogen-activated protein kinase kinase, MAPKK). The main role of serine phosphorylation is to allostere proteins to activate protein activity, primarily enzyme activity. In addition to allosteric phosphorylation and the activation of the protein, a more important function is that the binding protein provides a structural gene to promote its interaction with other proteins to form a multiprotein complex. The formation of a protein complex further promotes phosphorylation of the protein. Repeatedly, the signal generated by the initial protein phosphorylation is step by step. If a signal is generated that stimulates cell growth, this signal is eventually transferred to the nucleus, causing DNA replication and cell division.
Therefore, tyrosine phosphorylation and the formation of multiprotein complexes constitute the basic mechanism of cell signal transduction. Almost all polypeptide cell growth factors activate cells through this pathway and stimulate cell growth. Thus, enzymes that catalyze the phosphorylation of protein tyrosine, tyrosine kinases, make it a key mechanism for signal transduction mechanisms and for controlling cell growth. Tyrosine kinase and protein tyrosine phosphorylation also play a decisive role in tumorigenesis and growth. Many anti-tumor drugs have been developed with a focus on such molecules.
Post-translational modification of proteins is an important area of protein chemistry research. The more details about protein structure are understood, the broader the classification of protein post-translational modifications. Protein modifications include the attachment of a functional group such as a saccharide, a lipid, a nucleic acid, a phosphoric acid, a sulfuric acid, a carboxyl group, a methyl group, an acetyl group, or a hydroxyl group to a protein by a covalent bond. Proteins have been modified to give new functions in terms of binding, catalysis, regulation and physical properties. Protein phosphorylation is an important part of protein post-translational modification and plays an important role in the activity of enzymes and other important functional molecules, the second messenger transmission and the cascade of enzymes. Protein phosphorylation is accomplished by a series of protein kinases. This section focuses on the isolation and analysis of protein phosphokinases and the analysis of phosphorylated proteins.
Role in signal transduction: (1) Intracellular signaling proteins are mainly divided into two major categories: one is phosphorylated under the action of protein kinases, covalently bound to the phosphate group provided by ATP; the other is in the signal Combined with GTP, it usually replaces GDP with GTP.
(2) A common feature of these two intracellular signal proteins is that they are activated by obtaining one or more phosphoric acid groups when the signal is reached, and can be removed when the signal is weakened, thereby losing activity. In signal relay networks, phosphorylation of a certain signaling protein usually causes subsequent proteins to be phosphorylated in turn, forming a phosphorylation cascade.
(3) Phosphorylation of proteins is mainly concentrated on tyrosine, serine and threonine residues in the peptide chain. These residues have free hydroxyl groups and do not contain charges themselves. When phosphorylated, the protein is It has a charge, which changes the structure and further causes changes in protein activity, which is also the significance of protein phosphorylation.
1. Johnson LN.; et al. The effects of phosphorylation on the structure and function of proteins. Annual Review of Biophysics and Biomolecular Structure.1993, 22 (1): 199-232.