This is a family of cysteine proteases, found in actinobacteria, protobacteria and firmicutes. Papain-like cysteine proteases play a crucial role in plant-pathogen/pest interactions. On entering the host they act on non-self substrates, thereby manipulating the host to evade proteolysis [2]. AvrRpt2 from Pseudomonas syringae pv. tomato DC3000 triggers resistance to P. syringae-2-dependent defence responses, including hypersensitive cell death, by cleaving the Arabidopsis RIN4 protein which is monitored by the cognate resistance protein RPS2 [1].

1: Characterization of the Pseudomonas syringae pv. tomato AvrRpt2 protein: demonstration of secretion and processing during bacterial pathogenesis. Mudgett MB, Staskawicz BJ; Mol Microbiol. 1999;32:927-941. PMID:10361296

2: Papain-like cysteine proteases: key players at molecular battlefields employed by both plants and their invaders. Shindo T, Van der Hoorn RA; Mol Plant Pathol. 2008;9:119-125. PMID:18705889