The CLIP domain is a regulatory domain which controls the proteinase action of various proteins of the trypsin family, e.g. easter and pap2. The domain is restricted to the arthropoda and found in varying copy numbers (from one to five in Drosophila proteins). It is always found N-terminal to the chymotrypsin serine protease domain, which belong to MEROPS peptidase family S1A. The CLIP domain … expand

The CLIP domain is a regulatory domain which controls the proteinase action of various proteins of the trypsin family, e.g. easter and pap2. The domain is restricted to the arthropoda and found in varying copy numbers (from one to five in Drosophila proteins). It is always found N-terminal to the chymotrypsin serine protease domain, which belong to MEROPS peptidase family S1A. The CLIP domain remains linked to the protease domain after cleavage of a conserved residue which retains the protein in zymogen form. It is named CLIP because it can be drawn in the shape of a paper clip. It has many disulphide bonds and highly conserved cysteine residues, and so it folds extensively [ PUBMED:2107028 PUBMED:10696585 ].

The clip domain adopts an α/β mixed fold consisting of two helices and an antiparallel distorted β-sheet made of four strands. The two helices are antiparallel and are almost perpendicular to the β-sheet. Three disulfide bridges (C1-C5, C2-C4, C3-C6) stabilize the β-sheet, C3 being the only cysteine that is not located on a β-strand. The clip domain is located opposite the activation loop and contacts the C-terminal α-helix of the SP domain [ PUBMED:21310954 ].