Protein phosphatase 2C (PP2C) is involved in regulating cellular responses to stress in various eukaryotes. It consists of two domains: an N-terminal catalytic domain and a C-terminal domain characteristic of mammalian PP2Cs. This domain consists of three antiparallel alpha helices, one of which packs against two corresponding alpha-helices of the N-terminal domain. The C-terminal domain does not seem to play a role in catalysis, but it may provide protein substrate specificity due to the cleft that is created between it and the catalytic domain [1].

1: Crystal structure of the protein serine/threonine phosphatase 2C at 2.0 A resolution. Das AK, Helps NR, Cohen PT, Barford D; EMBO J 1996;15:6798-6809. PMID:9003755