Phosphopantothenate—cysteine ligase

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


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

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

Nomenclature
This enzyme belongs to the family of is_associated_with::ligases, specifically those forming carbon-nitrogen bonds as acid-D-amino-acid ligases (peptide synthases). 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 is_associated_with::gene.

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