PA_subtilisin_1: Protease-associated domain containing subtilisin-like proteases, subgroup 1. A subgroup of PA domain-containing subtilisin-like proteases. The significance of the PA domain to many of the proteins in which it is inserted is undetermined. 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. Proteins into which the PA domain is inserted include the following subtilisin-like proteases: i) melon cucumisin, ii) Arabidopsis thaliana Ara12, iii) Alnus glutinosa ag12, iv) members of the tomato P69 family, and v) tomato LeSBT2. However, these proteins belong to other subtilisin-like subgroups. Relatively little is known about proteins in this subgroup.