C-terminal processing peptidase; serine protease family S41
The C-terminal processing peptidase (CPP, EC 22.214.171.124) also known as tail-specific protease (tsp), the photosystem II D1 C-terminal processing protease (D1P), and other related S41 protease family members are present in this CD. CPP is synthesized as a precursor form with a carboxyl-terminal extension. It specifically recognizes a C-terminal tripeptide, Xaa-Yaa-Zaa, in which Xaa is preferably Ala or Leu, Yaa is preferably Ala or Tyr and Zaa is preferably Ala, but then cleaves at a variable distance from the C-terminus. The C-terminal carboxylate group is essential, and proteins where this group is amidated are not substrates. This family of proteases contains the PDZ domain that promotes protein-protein interactions and is important for substrate recognition. The active site consists of a serine/lysine catalytic dyad. The bacterial CCP-1 is believed to be important for the degradation of incorrectly synthesized proteins as well as protection from thermal and osmotic stresses. In E. coli, it is involved in the cleavage of a C-terminal peptide of 11 residues from the precursor form of penicillin-binding protein 3 (PBP3). In the plant chloroplast, the enzyme removes the C-terminal extension of the D1 polypeptide of photosystem II, allowing the light-driven assembly of the tetranuclear manganese cluster, which is responsible for photosynthetic water oxidation.