Open AccessPro-phenol oxidase activating proteinase from an insect, Manduca sexta: A bacteria-inducible protein similar to Drosophila easter
Author(s) -
Haobo Jiang,
Yan Wang,
Michael R. Kanost
Publication year - 1998
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.011
H-Index - 771
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.95.21.12220
Subject(s) - manduca sexta , prophenoloxidase , biochemistry , biology , zymogen , manduca , hemolymph , peptide sequence , complementary dna , serine protease , serine , microbiology and biotechnology , enzyme , innate immune system , insect , gene , protease , ecology , receptor
Activation of pro-phenol oxidase (proPO) in insects and crustaceans is important in defense against wounding and infection. The proPO zymogen is activated by a specific proteolytic cleavage. PO oxidizes phenolic compounds to produce quinones, which may help to kill pathogens and can also be used for synthesis of melanin to seal wounds and encapsulate parasites. We have isolated from the tobacco hornworm,Manduca sexta , a serine proteinase that activates proPO, and have cloned its cDNA. The isolated proPO activating proteinase (PAP) hydrolyzed artificial substrates but required other protein factors for proPO activation, suggesting that proPO-activating enzyme may exist as a protein complex, one component of which is PAP. PAP (44 kDa) is composed of two disulfide-linked polypeptide chains (31 kDa and 13 kDa). A cDNA for PAP was isolated from a hemocyte library, by using a PCR-generated probe based on the amino-terminal amino acid sequence of the 31-kDa catalytic domain. PAP belongs to a family of arthropod serine proteinases containing a carboxyl-terminal proteinase domain and an amino-terminal “clip” domain. The member of this family most similar in sequence to PAP is the product of theeaster gene fromDrosophila melanogaster . PAP mRNA was present at a low level in larval hemocytes and fat body, but became much more abundant in fat body after insects were injected withEscherichia coli . Sequence data and3 H-diisopropyl fluorphosphate labeling results suggest that the same PAP exists in hemolymph and cuticle.