| Description | HopAB family members 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 [ ]. AvrPtoB, also called HopAB3, is the best studied member of the family. It suppresses host basal defenses by interfering with PAMP (pathogen-associated molecular signature)-triggered immunity (PTI) through binding and inhibiting BAK1, a kinase which serves to activate defense signaling []. It also recognizes the kinase Pto to activate effector-triggered immunity (ETI) [].AvrPtoB contains an N-terminal region that contains 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) [ , ] . The family member HopPmaL is shorter and lacks the C-terminal E3 ligase domain [].The E3 ubiquitin ligase domain found in the bacterial protein AvrPtoB inhibits immunity-associated programmed cell death (PCD) when translocated into plant cells, probably by recruiting E2 enzymes and transferring ubiquitin molecules to cellular proteins involved in regulation of PCD and targeting them for degradation. The structure reveals a globular fold centred on a four-stranded β-sheet that packs against two helices on one face and has three very extended loops connecting the elements of secondary structure, with remarkable homology to the RING-finger and U-box families of proteins involved in ubiquitin ligase complexes in eukaryotes [ ]. | Name | Effector protein HopAB, E3 ubiquitin ligase domain |
| Short Name | E3_ubiquit_lig_AvrPtoB | Type | Domain |
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