title: Serine protease SP105 activates prophenoloxidase in Asian corn borer melanization, and is regulated by serpin-3.
abstract: Melanization reaction, resulting from the activation of prophenoloxidase, is a vital immune response in insects for encapsulating and killing the invasive organisms. Prophenoloxidase needs to be proteolytically activated by its upstream prophenoloxidase-activating protease (PAP) in melanization. Identification and characterization of PAPs facilitates the understanding of the molecular mechanisms involved in insect immunity. We here cloned a full-length cDNA for a serine protease, named as SP105, from Asian corn borer, Ostrinia furnacalis (Guenée). The open reading frame of SP105 encodes 424-amino acid residue protein with a 19-residue signal peptide. Sequence comparison indicates that SP105 is most similar to Manduca sexta PAP3, a defined prophenoloxidase-activating protease. qRT-PCR analysis showed that SP105 mRNA levels increased significantly after a bacterial injection. Recombinant SP105 directly cleaved and activated Asian corn borer prophenoloxidase and therefore acted as the prophenoloxidase-activating protease. Additionally, SP105 formed SDS-stable complexes with a serine protease inhibitor, serpin-3, and its activity in activating prophenoloxidase was efficiently inhibited by serpin-3. Our work thus illustrated a prophenoloxidase-activating protease and revealed its regulation by serpin-3. The results would allow further advances in the understanding of the melanization in Asian corn borer and other insects.
authors.affiliation: Department of Entomology, China Agricultural University, Beijing, 100193, China.
authors.forename: Yuan
authors.initials: Y
authors.lastname: Chu
authors.affiliation: Department of Entomology, China Agricultural University, Beijing, 100193, China.
authors.forename: Fang
authors.initials: F
authors.lastname: Hong
authors.affiliation: Department of Entomology, China Agricultural University, Beijing, 100193, China.
authors.forename: Qizhi
authors.initials: Q
authors.lastname: Liu
authors.affiliation: Department of Entomology, China Agricultural University, Beijing, 100193, China.
authors.forename: Chunju
authors.initials: C
authors.lastname: An
mesh_terms: D000818:Animals; D004156:Catechol Oxidase / Q000378:metabolism; D003001:Cloning, Molecular; D004792:Enzyme Precursors / Q000378:metabolism; D019476:Insect Proteins / Q000235:genetics / Q000378:metabolism*; D007915:Lepidoptera / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D017385:Sequence Homology; D057057:Serine Proteases / Q000235:genetics / Q000378:metabolism*; D015843:Serpins / Q000378:metabolism
chemical_list: D004792:Enzyme Precursors; D019476:Insect Proteins; D015843:Serpins; C038451:pro-phenoloxidase; D004156:Catechol Oxidase; D057057:Serine Proteases