AcpS

AcpS, or acyl carrier protein synthase, is a 4'-phosphopantetheinyl transferase (PPTase) that activates the bacterial acyl carrier protein (ACP) by converting apo-ACP to holo-ACP. This activation occurs when AcpS transfers the 4'-phosphopantetheine moiety from coenzyme A to a conserved serine residue on ACP, enabling ACP to carry growing fatty acyl chains during fatty acid biosynthesis.

AcpS enzymes are typically organized as homotrimers, with each subunit contributing to the catalytic site that coordinates CoA and ACP during the transfer reaction. They generally show specificity for ACPs associated with the type II fatty acid synthesis pathway (FAS II) in bacteria and are less able to activate other carrier proteins, in contrast to the broader-specificity Sfp-type PPTases, which can modify a wider range of carrier proteins including those involved in polyketide and nonribosomal peptide biosynthesis.

Distribution and role in metabolism vary among bacteria. The acpS gene is widely conserved in many bacterial lineages that rely on FAS II, and in several species it is essential for viability because holo-ACP is required for fatty acid production. Some bacteria possess additional or alternative PPTases that can partially compensate for AcpS loss, reflecting diversification of phosphopantetheinyl transfer mechanisms.

Biological significance and applications: AcpS is central to fatty acid biosynthesis in many bacteria and thus represents a potential target for antibacterial strategies. In biotechnology, understanding AcpS specificity informs strategies for engineering carrier protein modification, particularly when aiming to harness or reprogram microbial lipid or polyketide pathways.