This domain is found at the very C-terminus of bacteriophage parallel beta-helical tailspike proteins. It carries the enzymic residues that induce autoproteolytic cleavage to bring about maturation of the folding process of the helix in a chaperone-like manner. The domain thus mediates the assembly of a large tailspike protein and then releases itself after maturation. These C-terminal regions that autoproteolytically release themselves after maturation are exchangeable between functionally unrelated N-terminal proteins and have been identified in a number of bacteriophage tailspike proteins [1].

1: Knitting and snipping: chaperones in beta-helix folding. Schulz EC, Ficner R; Curr Opin Struct Biol. 2011; [Epub ahead of print] PMID:21330133