rtxA

rtxA is the designation for several bacterial genes that encode repeats-in-toxin (RTX) family toxins, most prominently the multifunctional autoprocessing RTX (MARTX) toxins produced by various Vibrio species. In Vibrio vulnificus, for example, rtxA1 encodes a very large secreted toxin that carries multiple catalytic and binding modules; other strains or species may harbor variants such as rtxA2. The RTX repeats at the toxin termini bind calcium and are characteristic of this toxin family; the central portion contains effector domains that determine specific cellular targets.

MARTX toxins are secreted by the Type I secretion system; they are produced as single polypeptides and undergo autoproteolytic processing by a cysteine protease domain to release effector modules into host cells.

Effector domains can include actin cross-linking domain, Rho-inactivation domain, glucosyltransferase domain, deamidase domain, and others; combinations define the toxin’s activity. The result is disruption of the actin cytoskeleton, altered signaling, cell rounding, cytotoxicity, and sometimes cell death. In human infections, MARTX/rtxA toxins contribute to tissue damage and immune modulation and are associated with virulence in Vibrio vulnificus and related pathogens.

Genetic context and variation: rtxA genes are often located within pathogenicity islands or operons that include an acyltransferase gene (rtxC) required for toxin maturation; there can be multiple alleles, such as rtxA1 and rtxA2, encoding toxins with differing effector repertoires and potencies. The genes may be carried on chromosomes, plasmids, or genomic islands, contributing to strain-to-strain variability in virulence. Research focuses on the regulation, secretion, and posttranslational processing of RtxA/MARTX toxins, as well as the specific roles of individual effector domains.