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What Amino Acids Can be Phosphorylated?



what amino acids can be phosphorylated

If you are a science student, you might come across the question “What amino acids can be phosphorylated?’. Basically, there are only three common amino acids that can be phosphorylated: serine, threonine, and tyrosine. Protein phosphorylation is another name for amino acids phosphorylation. This topic seems a bit complex, however, it is a very simple thing. To have a deeper knowledge of this topic and solve your questions easily, you must have the basic concepts clear. Hence, in this guide, we will be providing you with all the information you need to ace this topic.

What Are Amino Acids?

what amino acids can be phosphorylated

An image of amino acids under a microscope.

Amino acids are the building blocks of a protein. Carbon, hydrogen, oxygen, and nitrogen are the four essential constituents of amino acids, while extra elements can be present in the side chains. These acids are organic compounds having the amine functional group (-NH2) and the Carboxyl group (-COOH). Some of the most common amino acids are; valine, glutamine, and threonine. which is one of the amino acids that can be phosphorylated. Every amino acid has a unique side chain attached to them. Amino Acids combine like a chain to form a protein that will then phosphorylate into a protein phosphatase.

What is Protein Phosphorylation?

In the easiest possible words, protein phosphorylation is the addition of the phosphate group in a protein. Phosphorylation is a reversible post-translation modification to regulate proteins. Protein kinases, a vast class of enzymes, catalyze this process. The phosphate group adds to the amino acid residue of the protein. Phosphorylation affects protein activity by influencing their intracellular positions, activity with other proteins, and protease breakdown.

Protein kinases (the enzyme) removes the phosphate group from the high-energy molecule adenosine triphosphate (ATP), which triggers chemical reactions in the human body. The ATP molecules which are in charge of the free energy in our body react with the hydroxyl group of an amino acid in the presence of the enzyme, protein kinases, to form ADP. This pushes one phosphate from ATP towards the amino acid residue. As a result, protein phosphorylation occurs as phosphate adds to the protein. Finally, we get the phosphor amino acid and an ADP molecule.

Moreover, this is a reversible reaction and dephosphorylation can also occur. The other enzymes class known as protein phosphatases is responsible for dephosphorylating phosphoprotein. Dephosphorylation is the complete opposite of phosphorylation, just as the name suggests. It is the removal of phosphate from the proteins. Moreover, it occurs by reacting the hydroxyl group to the phosphor amino acid in the presence of the correct enzyme, which is protein phosphatases.

What Amino Acids Can be Phosphorylated?

what amino acids can be phosphorylated

phosphor amino acids

According to research conducted by Kinexus on phosphorylation, proteins are generally phosphorylated once per 17 amino acids. Serine, threonine, and tyrosine are the amino acids that go through phosphorylation most frequently in eukaryotes. While histidine phosphorylates in both prokaryotes and plants. Other amino acids that can be phosphorylated post-translationally include arginine, lysine, aspartic acid, glutamic acid, and cysteine. Many biological activities, such as the cell cycle, proliferation, apoptosis, and signal transduction pathways, are regulated by phosphorylation. Phosphorylation of amino acids is the most common way for proteins to regulate their function and for signals to be transmitted throughout the cell.


In a variety of biological activities, the phosphorylation of tyrosine residues in proteins modulates cell communication. Cell growth, reproduction, differentiation, migration, longevity, and fatality are just a few examples. The activation of PTks by extracellular stimulation that ligands induce. It occurs because the production of reactive oxygen species, such as H2O2, links to the activation of tyrosine phosphorylation signaling. Peptide growth factors, cytokines, and agonists to G-protein-coupled receptors all induce these signals. You may notice that sometimes you feel like you are radiating positivity that also might be because of hormonal changes that induce the signals.

During phosphotyrosine signaling, protein tyrosine phosphorylation (PTP) serves as an oxidation sensor. The chemical foundation for PTP oxidation has its signaling outputs in a range of paths having a role in pathophysiological situations.  Furthermore, scientists believe that PTP S-nitrosylation regulates phosphotyrosine signaling via redox-dependent modulation of PTP activity that nitric oxide generates.

Serine and Threonine

These two amino acids play similar roles during and after phosphorylation. Cell proliferation, programmed cell death (apoptosis), cell differentiation, and embryonic development are all regulated by Serine or Threonine Kinase ligands. These are two main amino acids that can be phosphorylated. Phosphorylation of serine and threonine residues often interact with serine and threonine residues with O-GlcNAc modifications. On serine and threonine residues of nucleocytoplasmic proteins, O-GlcNAc is a reversible enzymatic post-translational modification. A glycosidic link between the hydroxyl group of the serine or threonine side chains and N-acetylglucosamine characterizes the alteration. Serine or threonine phosphorylation also implicates in the regulation of the apoptosis-controlling Bcl-2 protein, since some phosphorylation events that cytokines generate like IL-3 are anti-apoptotic. While the others caused by chemotherapy treatments are pro-apoptotic.


what amino acids can be phosphorylated

Skeletal structure of Histidine

Histidine is an amino acid that is a must for the production of proteins. It has an amine functional group, a carboxylic acid functional group, and an imidazole side chain. Imidazole is a soluble solid organic compound with the formula C3N2H4 that is white in color. Unlike threonine, serine, and tyrosine that phosphorylate in eukaryotes, Histidine phosphorylates in plants and prokaryotes. Eukaryotes are cells or organisms that have a very clear structure of a nucleus. Whereas, prokaryotes, like bacteria, are small organisms with only one cell. They lack outlining of the nucleus with a membrane and other specialized organelles.

In prokaryotes, histidine phosphorylation is crucial, and it accounts for around 6% of total phosphorylation in eukaryotes. Despite this, phosphohistidine residues do not appear much in proteins due to rapid phosphoryl group hydrolysis in acidic environments. The bacterial phosphoenolpyruvate: sugar phosphotransferase system (PTS), bacterial two-component systems, and reactions catalyzed by enzymes like nucleoside diphosphate kinase and succinyl–CoA synthetase all use phosphohistidines.


Threonine, tyrosine, and serine are three amino acids that regularly phosphorylate. Histidine can also phosphorylate but in prokaryotes rather than eukaryotes like the other three. Protein activity and interactions with other proteins are all effects of the phosphorylation of amino acids.

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