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Publication Abstract from PubMed

Clip-domain serine proteases (SPs) are the essential components of extracellular signaling cascades in various biological processes, especially in embryonic development and the innate immune responses of invertebrates. They consist of a chymotrypsin-like SP domain and one or two clip domains at the N-terminus. Prophenoloxidase-activating factor (PPAF)-II, which belongs to the noncatalytic clip-domain SP family, is indispensable for the generation of the active phenoloxidase leading to melanization, a major defense mechanism of insects. Here, the crystal structure of PPAF-II reveals that the clip domain adopts a novel fold containing a central cleft, which is distinct from the structures of defensins with a similar arrangement of cysteine residues. Ensuing studies demonstrated that PPAF-II forms a homo-oligomer upon cleavage by the upstream protease and that the clip domain of PPAF-II functions as a module for binding phenoloxidase through the central cleft, while the clip domain of a catalytically active easter-type SP plays an essential role in the rapid activation of its protease domain.

Crystal structure of a clip-domain serine protease and functional roles of the clip domains.,Piao S, Song YL, Kim JH, Park SY, Park JW, Lee BL, Oh BH, Ha NC EMBO J. 2005 Dec 21;24(24):4404-14. Epub 2005 Dec 15. PMID:16362048^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.