IgaA (intracellular growth attenuator A) is a conserved bacterial membrane protein involved in the negative regulation of the Rcs phosphorelay system, a signaling pathway that controls envelope stress responses in many Gram-negative bacteria. The protein is essential for bacterial viability in several species, including Salmonella enterica, and plays a key role in modulating growth and virulence.

IgaA is a multi-pass inner membrane protein that suppresses activation of the RcsCDB phosphorelay system under non-stress conditions. When functioning properly, IgaA prevents unnecessary activation of envelope stress responses, helping maintain homeostasis and prevent toxic overexpression of capsular polysaccharides and other surface components.

Loss-of-function mutations in igaA lead to constitutive activation of Rcs signaling, resulting in defects in cell division, envelope structure, and motility, and in some cases a reduction in virulence.

IgaA typically contains several transmembrane domains and a cytoplasmic tail that may interact with downstream regulators. It is classified under the Pfam protein family Pfam PF07095.

IgaA is essential for intracellular survival and growth in host cells in some pathogenic bacteria. Its role in virulence regulation makes it a potential target for antibacterial strategies aimed at disabling stress adaptation mechanisms.

Orthologs of IgaA have been identified in a wide range of Enterobacteriaceae species, including Escherichia coli, Yersinia pestis, and Shigella flexneri.