PA_subtilisin_like: Protease-associated domain containing subtilisin-like proteases. This group contains various PA domain-containing subtilisin-like proteases including melon cucumisin, Arabidopsis thaliana Ara12, a nodule specific serine protease from Alnus glutinosa ag12, members of the tomato P69 family, and tomato LeSBT2. These proteins belong to the peptidase S8 family. Cucumisin from the juice of melon fruits is a thermostable serine peptidase, with a broad substrate specificity for oligopeptides and proteins. A. thaliana Ara12 is a thermostable, extracellular serine protease, found chiefly in silique tissue and stem tissue. Ara12 is stimulated by Ca2+ ions. A. glutinosa ag12 is expressed at high levels in the nodules, and at low levels in the shoot tips; it is implicated in both symbiotic and non-symbiotic processes in plant development. The tomato P69 protease family is comprised of various protein isoforms of approximately 69KDa. These isoforms accumulate extracellularly. Some of the P69 genes are tightly regulated in a tissue specific fashion, and by environmental and developmental signals. For example: infection with avirulent bacteria activates transcription of the genes for the P69 B and C isoforms, the P69 E transcript was detected only in roots, and the P69F transcript only in hydathodes. The Tomato LeSBT2 subtilase transcript was not detected in flowers and roots, but was present in cotyledons and leaves. The significance of the PA domain to these proteins has not been ascertained. It may be a protein-protein interaction domain. At peptidase active sites, the PA domain may participate in substrate binding and/or promoting conformational changes, which influence the stability and accessibility of the site to substrate.
Jiyao W et al.(2023). "The conserved domain database in 2023.",