CagD is a tightly conserved family of proteins found in the pathogenic strains of Helicobacter species. It is one of some 30 proteins, produced from the genomic insert termed the pathogenicity island, required for the type IV secretion system - T4SS - that delivers CagA oncoprotein toxin into the host cell. CagD is a covalent dimer in which each monomer folds as a single domain composed of five beta-strands and three alpha-helices. CagD partially associates with the inner membrane, where it may be exposed to the periplasmic space; this may indicate that CagD is released into the supernatant during host cell infection in order then to bind to the host cell surface, or to be incorporated into the pilus structure [1].

1: The Helicobacter pylori CagD (HP0545, Cag24) protein is essential for CagA translocation and maximal induction of interleukin-8 secretion. Cendron L, Couturier M, Angelini A, Barison N, Stein M, Zanotti G; J Mol Biol. 2009;386:204-217. PMID:19109970