The acyl carrier proteins of lipid synthesis are busy having other affairs.

This is a review of the acyl carrier proteins (ACPs) of type II fatty acid synthesis in bacteria and mitochondria, their structures and protein interactions. Type II fatty acid synthesis in bacteria (Prog. Lipid Res. (2013) 52, 249-276; Biochim. Biophys. Acta (1996) 1302, 1-16; Annu. Rev. Biochem. (2005) 74, 791-831) and in the mitochondria of yeast and mammals (Biochim. Biophys. Acta Mol. Cell. Res. (2019) 1866, 118540; MedChemComm (2019) 10, 209-220; Elife (2016) 5, e17828; Mol. Cell (2018) 71, 567-580.e4) will be discussed only tangentially in this review. The above references are excellent recent reviews. Bacterial fatty acid synthesis has been a popular target for the development of new antimicrobials and an up-to-date review of the field has been published (Annu. Rev. Microbiol. (2022) 76, 281-304). The ACP-like proteins of secondary metabolites (e.g. polyketide synthesis will not be reviewed). Escherichia coli ACP is now called AcpP to distinguish it from the enzymes that attach (AcpS) and remove (AcpH) the 4'-phosphopantetheine (4'PP) prosthetic group. Note that the primary translation product of the acpP gene is called apo-AcpP. The addition of the 4'PP prosthetic group converts apo-AcpP to holo-AcpP (commonly referred to as AcpP). Acylation of the 4'PP prosthetic group gives acyl-AcpP species. The length of the acyl chain determines the properties of the acyl-AcpP as will be discussed below.