Structural domains comprising this superfamily share the structure of the BAK1 binding domain found in members of the HopAB family of proteins. These are type III effector proteins that are secreted by the plant pathogen Pseudomonas syringae into the host plant to inhibit its immune system and facilitate the spread of the pathogen PMID:15808932. The best studied member of this family, HopAB3/AvrPtoB, suppresses host basal defenses by interfering with PAMP (pathogen-associated molecular signature)-triggered immunity (PTI) by the binding and inhibiton of BAK1, a kinase which serves to activate defense signaling PMID:22169508. It also recognizes the kinase Pto to activate effector-triggered immunity (ETI) PMID:21112235.

HopAB3 contains an N-terminal region comprised of two kinase-interacting domains (KID) and a C-terminal E3 ligase domain. The first KID recognizes the PTI-associated kinase Bti9 as well as Pto, and is referred to as the Pto-binding domain (PID). The second KID interacts with BAK1 and FLS2, which are leucine-rich repeat-containing receptor-like kinases, and is called the BAK1-interacting domain (BID) PMID:22169508,PMID:19062288.