Phosphopantothenate—cysteine ligase

In enzymology, a phosphopantothenate—cysteine ligase also known as phosphopantothenoylcysteine synthetase (PPCS) is an enzyme  that catalyzes the chemical reaction which constitutes the second of five steps involved in the conversion of pantothenate to Coenzyme A. The reaction is:


 * NTP + (R)-4'-phosphopantothenate + L-cysteine $$\rightleftharpoons$$ NMP + diphosphate + N-[(R)-4'-phosphopantothenoyl]-L-cysteine

The nucleoside triphosphate (NTP) involved in the reaction varies from species to species. Phosphopantothenate—cysteine ligase from the bacterium Escherichia coli uses cytidine triphosphate (CTP) as an energy donor, whilst the human isoform uses adenosine triphosphate (ATP).

Nomenclature
This enzyme belongs to the family of ligases, specifically those forming carbon-nitrogen bonds as acid-D-amino-acid ligases (peptide syntheses). The systematic name of this enzyme class is (R)-4'-phosphopantothenate:L-cysteine ligase. This enzyme is also called phosphopantothenoylcysteine synthetase.

Gene
Phosphopantothenoylcysteine synthetase in humans is encoded by the PPCS gene.

Protein structure
As of late 2007, 5 structures have been solved for this class of enzymes, with PDB accession codes, , , , and.