Holo-(acyl-carrier-protein) synthase

In enzymology and molecular biology, a holo- synthase is an enzyme that catalyzes the chemical reaction:
This enzyme belongs to the family of transferases, specifically those transferring non-standard substituted phosphate groups, and more specifically to the 4'-phosphopantetheinyl transferases named after the group they transfer.
In mammals, this activity is performed by the PPTase, aminoadipate-semialdehyde dehydrogenase-phosphopantetheinyl transferase, which acts in both the cytosol and mitochondria and also modifies non-acyl carrier protein substrates.

Function

All ACPS enzymes known so far are evolutionally related to each other in a single superfamily of proteins. It transfers a 4'-phosphopantetheine moiety from coenzyme A to an invariant serine in an acyl carrier protein, a small protein responsible for acyl group activation in fatty acid biosynthesis. This post-translational modification renders holo-ACP capable of acyl group activation via thioesterification of the cysteamine thiol of 4'-PP. This superfamily consists of two subtypes: the trimeric ACPS type such as E. coli ACPS and the monomeric Sfp type such as B. subtilis SFP. Structures from both families are now known. The active site accommodates a magnesium ion. The most highly conserved regions of the protein are involved in binding the magnesium ion.

Nomenclature

The systematic name of this enzyme class is CoA-:apo- 4'-pantetheinephosphotransferase. Other names in common use, disregarding the synthetase/synthase spelling difference, include acyl carrier protein holoprotein synthetase, holo-ACP synthetase, coenzyme A:fatty acid synthetase apoenzyme 4'-phosphopantetheine, acyl carrier protein synthetase, PPTase, acyl carrier protein synthase, P-pant transferase, and CoA:apo- pantetheinephosphotransferase.

Structural studies

As of late 2007, 8 structures have been solved for this class of enzymes, with PDB accession codes,,,,,,, and.