Figure 3.

Acyl carrier protein post-translational manipulations and modifications. Carrier proteins (CPs) come from the ribosome in its naked apo-form (blue circle). By the action of a PPTase, utilizing coenzyme A, a highly conserved serine residue of the CP is post-translationally modified with a 4′-phosphopantetheine arm forming holo-ACP (yellow circle). This active form of the carrier protein is used to carry the growing fatty acid chain, by action of the FAS enzymes (acyl-ACP, red circle). A thioesterase (TE) or acyltransferase (AT) can cleave off the fatty acid, regenerating holo-CP. The adenylate-forming enzyme acyl-ACP synthetase (AasS) can directly load a fatty acid onto holo-CP, resulting in acyl-ACP (red circle). In the laboratory, it is possible to attach pantetheine-probes, in a CoaA, -D, -E and PPTase Sfp dependent fashion, to apo-CP, leading to crypto-CP (pink circle). Acyl carrier protein hydrolase or phosphodiesterase, AcpH, can regenerate the apo-form of the carrier protein from acyl-, crypto- and holo-ACP.