Pantothenate kinase (EC 2.7.1.33, PanK; CoaA) is the first enzyme in the Coenzyme A (CoA) biosynthetic pathway. It phosphorylates pantothenate (vitamin B₅) to form 4'-phosphopantothenate at the expense of a molecule of adenosine triphosphate (ATP). It is the rate-limiting step in the biosynthesis of CoA.

CoA is a necessary cofactor in all living organisms. It acts as the major acyl group carrier in many important cellular processes, such as the citric acid cycle (tricarboxylic acid cycle) and fatty acid metabolism. Consequently, pantothenate kinase is a key regulatory enzyme in the CoA biosynthetic pathway.

Three distinct types of PanK has been identified - PanK-I (found in bacteria), PanK-II (mainly found in eukaryotes, but also in the Staphylococci) and PanK-III, also known as CoaX (found in bacteria). Eukaryotic PanK-II enzymes often occur as different isoforms, such as PanK1, PanK2, PanK3 and PanK4. In humans, multiple PanK isoforms are expressed by four genes. PANK1 gene encodes the PanK1α and PanK1β forms, and PANK2 and PANK3 encode PanK2 and PanK3, respectively.

PanK-II contains two protein domains, as illustrated in Figure 1. The A domain and A' domain each has a glycine-rich loop (sequence GXXXXGKS; P loop) that is characteristic of nucleotide-binding sites; this is where ATP is assumed to bind. located between residues 95 and 102 on the A domain

The two ATP binding sites display cooperative behavior. The dimerization interface consists of two long helices, one from each monomer, that interact with each other. The C-terminal ends of the helices are held together by van der Waals interactions between valine and methionine residues of each monomer. The middle of the helices is attached by hydrogen bonds between asparagine residues. At the N-terminal end, each helix widens and forms a four-helix bundle with two shorter helices. This bundle consists of a hydrophobic core formed by non-polar residues that utilize van der Waals forces to further stabilize the dimer.

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