The acyl carrier protein (ACP) is an important component in both fatty acid

Fatty acid

In chemistry, especially biochemistry, a fatty acid is a carboxylic acid with a long unbranched aliphatic tail , which is either saturated or unsaturated. Most naturally occurring fatty acids have a chain of an even number of carbon atoms, from 4 to 28. Fatty acids are usually derived from...

 and polyketide

Polyketide

Polyketides are secondary metabolites from bacteria, fungi, plants, and animals. Polyketides are usually biosynthesized through the decarboxylative condensation of malonyl-CoA derived extender units in a similar process to fatty acid synthesis...

 biosynthesis with the growing chain bound during synthesis as a thiol ester at the distal thiol of a 4'-phosphopantethiene moiety. The protein is expressed in the inactive apo form and the 4'-phosphopantetheine moiety must be post-translationally attached to a conserved serine residue on the ACP by the action of holo-acyl carrier protein synthase

Acyl carrier protein synthase

Acyl carrier protein synthases are members of the family of phosphopantethienyl transferases responsible for the conversion of the inactive apo-Acyl carrier protein from fatty acid or polyketide biosynthesis into the active holo form through the post-translational addition of a...

 (ACPS), a phosphopantetheinyl transferase.

4'-Phosphopantetheine

Phosphopantetheine

4'-Phosphopantetheine is an essential prosthetic group of acyl carrier protein and peptidyl carrier proteins and aryl carrier proteins derived from Coenzyme A...

 is an essential prosthetic group of several acyl carrier proteins involved in pathways of primary and secondary metabolism including the acyl carrier proteins (ACP) of fatty acid synthase

Fatty acid synthase

Fatty acid synthase is an enzyme that in humans is encoded by the FASN gene.Fatty acid synthase is a multi-enzyme protein that catalyzes fatty acid synthesis...

s, ACPs of polyketide synthase

Polyketide synthase

Polyketide synthases are a family of multi-domain enzymes or enzyme complexes that produce polyketides, a large class of secondary metabolites, in bacteria, fungi, plants, and a few animal lineages...

s, and peptidyl carrier proteins (PCP) and aryl carrier proteins (ArCP) of nonribosomal peptide synthetases (NRPS). Phosphopantetheine fulfills two demands in these biosynthetic pathways. First, the intermediates remain covalently linked to the synthases (or synthetases) in an energy-rich linkage. Second, the flexibility and length of the phosphopantetheine chain (approximately 2 nm) allows the covalently tethered intermediates to have access to spatially-distinct enzyme-active sites. This increases the effective molarity of the intermediate and allows an assembly line-like process.

The ACPs are small negatively-charged α-helical bundle proteins with a high degree of structural and amino acid similarity. The structures of a number of acyl carrier proteins have been solved using various NMR and crystallography techniques.

The ACPs are related in structure and mechanism to the peptidyl carrier proteins (PCP) from nonribosomal peptide

Nonribosomal peptide

Nonribosomal peptides are a class of peptide secondary metabolites, usually produced by microorganisms like bacteria and fungi. Nonribosomal peptides are also found in higher organisms, such as nudibranchs, but are thought to be made by bacteria inside these organisms...

synthases.