2olg
Crystal structure of the serine protease domain of prophenoloxidase activating factor-I in a zymogen form
Structural highlights
FunctionPPAF1_HOLDI Serine endopeptidase which, by cleaving prophenoloxidase PPO1 and PPO2, is required for the activation of the prophenoloxidase cascade probably following the recognition of pathogen-derived products.[1] [2] [3] [4] [5] Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedA family of serine proteases (SPs) mediates the proteolytic cascades of embryonic development and immune response in invertebrates. These proteases, called easter-type SPs, consist of clip and chymotrypsin-like SP domains. The SP domain of easter-type proteases differs from those of typical SPs in its primary structure. Herein, we report the first crystal structure of the SP domain of easter-type proteases, presented as that of prophenoloxidase activating factor (PPAF)-I in zymogen form. This structure reveals several important structural features including a bound calcium ion, an additional loop with a unique disulfide linkage, a canyon-like deep active site, and an exposed activation loop. We subsequently show the role of the bound calcium and the proteolytic susceptibility of the activation loop, which occurs in a clip domain-independent manner. Based on biochemical study in the presence of heparin, we suggest that PPAF-III, highly homologous to PPAF-I, contains a surface patch that is responsible for enhancing the catalytic activity through interaction with a nonsubstrate region of a target protein. These results provide insights into an activation mechanism of easter-type proteases in proteolytic cascades, in comparison with the well studied blood coagulation enzymes in mammals. Crystal structure of the serine protease domain of prophenoloxidase activating factor-I.,Piao S, Kim S, Kim JH, Park JW, Lee BL, Ha NC J Biol Chem. 2007 Apr 6;282(14):10783-91. Epub 2007 Feb 7. PMID:17287215[6] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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