enzymology Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. A ...

, arginine kinase () is an

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. A ...

that

catalyzes Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...

the

chemical reaction A chemical reaction is a process that leads to the IUPAC nomenclature for organic transformations, chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the pos ...

:ATP + L-arginine

\rightleftharpoons

ADP + N^ω-phospho-L-arginine Thus, the two substrates of this enzyme are ATP and

L-arginine Arginine is the amino acid with the formula (H2N)(HN)CN(H)(CH2)3CH(NH2)CO2H. The molecule features a guanidino group appended to a standard amino acid framework. At physiological pH, the carboxylic acid is deprotonated (−CO2−) and both the am ...

, whereas its two

products Product may refer to: Business * Product (business), an item that serves as a solution to a specific consumer problem. * Product (project management), a deliverable or set of deliverables that contribute to a business solution Mathematics * Produ ...

are ADP and N^ω-phospho-L-arginine. Unlike the phosphoester bond, formed during the phosphorylation of serine, threonine or tyrosine residues, the phosphoramidate (P-N bond) in phospho-arginine is unstable at low pH (<8), making it difficult to detect with the traditional mass spectrometry protocols. Arginine kinase belongs to the family of

transferase A transferase is any one of a class of enzymes that catalyse the transfer of specific functional groups (e.g. a methyl or glycosyl group) from one molecule (called the donor) to another (called the acceptor). They are involved in hundreds of di ...

s, specifically those transferring phosphorus-containing groups (

phosphotransferase Phosphotransferases are a category of enzymes ( EC number 2.7) that catalyze phosphorylation reactions. The general form of the reactions they catalyze is: :A-P + B \rightleftharpoons B-P + A Where ''P'' is a phosphate group and A and B are the do ...

s) with a nitrogenous group as acceptor. This enzyme participates in

arginine and proline metabolism Arginine and proline metabolism is one of the central pathways for the biosynthesis of the amino acids arginine and proline from glutamate. The pathways linking arginine, glutamate, and proline are bidirectional. Thus, the net utilization or prod ...

Nomenclature

The

systematic name A systematic name is a name given in a systematic way to one unique group, organism, object or chemical substance, out of a specific population or collection. Systematic names are usually part of a nomenclature. A semisystematic name or semitrivial ...

of this enzyme class is * ATP:L-arginine N^ω-phosphotransferase Other names in common use include * arginine phosphokinase, * adenosine 5'-triphosphate: L-arginine phosphotransferase, * adenosine 5'-triphosphate-arginine phosphotransferase, * ATP:L-arginine N-phosphotransferasel ATP:L-arginine, and * ω-N-phosphotransferase.

Function

In Gram-positive bacteria, such as ''

Bacillus subtilis ''Bacillus subtilis'', known also as the hay bacillus or grass bacillus, is a Gram-positive, catalase-positive bacterium, found in soil and the gastrointestinal tract of ruminants, humans and marine sponges. As a member of the genus ''Bacillu ...

'', the arginine kinase McsB phosphorylates the arginine residues on incorrectly folded or aggregated proteins to target them for degradation by the bacterial protease ClpC-ClpP (ClpCP).The phospho-arginine (pArg) modification is recognised by the N-terminal domain of ClpC, the protein-unfolding subunit of the ClpCP protease. Following recognition, the target protein is degraded by the ClpP subunit which has protease activity. Since phosphorylation reverses arginine's charge, the pArg modification has an unfolding effect on the target protein, easing its proteolytic degradation. Arginine phosphorylation is a dynamic post-translational modification, which can also be reversed by pArg-specific phosphatases, such as the bacterial YwlE. The pArg-ClpCP mechanism for protein degradation in bacteria is analogous to the eukaryotic

ubiquitin-proteasome system Proteasomes are protein complexes which degrade unneeded or damaged proteins by proteolysis, a chemical reaction that breaks peptide bonds. Enzymes that help such reactions are called proteases. Proteasomes are part of a major mechanism by whi ...

. Several studies have reported the presence of arginine kinases in eukaryotes. A recent study identified arginine phosphorylation on 118 proteins in

Jurkat cells Jurkat cells are an immortalized line of human T lymphocyte cells that are used to study acute T cell leukemia, T cell signaling, and the expression of various chemokine receptors susceptible to viral entry, particularly HIV. Jurkat cells can prod ...

, which were primarily proteins with DNA/RNA-binding activities. The function of arginine phosphorylation in eukaryotes however is still unknown.

Structural studies

As of late 2007, 8

structures A structure is an arrangement and organization of interrelated elements in a material object or system, or the object or system so organized. Material structures include man-made objects such as buildings and machines and natural objects such as ...

have been solved for this class of enzymes, with PDB accession codes , , , , , , , and .

Nomenclature

Function

Structural studies

References

Further reading