AatD

AatD is an enzyme found in certain Gram-negative bacteria, where it functions as an N-acyltransferase within the Aat secretion system. It is most closely associated with pathogenic strains of Escherichia coli that produce the heat-stable enterotoxin STa and other small secreted peptides.

The primary role of AatD is to catalyze the N-acylation of exported peptides, most notably the precursor to STa. By transferring a fatty acyl group to the N-terminal amino group of these substrates, AatD creates an N-acylated form that is typically required for efficient recognition and export by the AatPABCD secretion machinery. AatD belongs to a family of bacterial N-acyltransferases that use fatty acyl donors, such as fatty acyl-ACP, to modify target proteins or peptides, a modification that can influence substrate stability and secretion.

Genetically, AatD is encoded in the aat gene region alongside other components of the Aat secretion system. This cluster is present in enterotoxigenic E. coli and related organisms that rely on the Aat pathway to secrete virulence factors. The enzyme’s activity links peptide processing with secretion, contributing to virulence by enabling proper toxin maturation and export.

Understanding AatD has implications for studying bacterial secretion systems and for exploring potential therapeutic approaches aimed at mitigating toxin delivery in Aat-dependent pathogens. Its functioning illustrates how post-translational lipid modification can govern virulence factor secretion in bacteria.