A pattern recognition serine proteinase triggers the prophenoloxidase activation cascade in the tobacco hornworm, Manduca sexta.
A serine proteinase cascade in insect hemolymph mediates prophenoloxidase activation, a defense mechanism against pathogen or parasite infection. Little is known regarding its initiating proteinase or how this enzyme is activated in response to invading microorganisms. We have isolated from the tobacco hornworm, Manduca sexta, a cDNA encoding a modular protein designated hemolymph proteinase 14 (HP14). It contains five low density lipoprotein receptor class A repeats, a Sushi domain, a unique Cys-rich region, and a proteinase-catalytic domain. The HP14 mRNA exists in fat body and hemocytes of the naive larvae, and its level increases significantly at 24 h after a bacterial challenge. We expressed proHP14 with a carboxyl-terminal hexahistidine tag in a baculovirus/insect cell system and detected the recombinant protein in two forms. The 87-kDa protein was primarily intracellular, whereas the 75-kDa form was present in the medium. Interaction with peptidoglycan resulted in proteolytic processing of the purified zymogen and generation of an amidase activity. Supplementation of hemolymph with proHP14 greatly enhanced prophenoloxidase activation in response to Micrococcus luteus. These data suggest that proHP14 is a pattern recognition protein that binds to bacteria and autoactivates and triggers the prophenoloxidase activation system in the hemolymph of M. sexta.
Ji
Chuanyi
C
Department of Entomology and Plant Pathology, Oklahoma State University, Stillwater, OK 74078, USA.
Wang
Yang
Y
Guo
Xiaoping
X
Hartson
Steve
S
Jiang
Haobo
H
D000595:Amino Acid Sequence; D000818:Animals; D016367:Baculoviridae / Q000378:metabolism; D001483:Base Sequence; D004156:Catechol Oxidase / Q000737:chemistry*; D003545:Cysteine / Q000737:chemistry; D018076:DNA, Complementary / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D010450:Endopeptidases / Q000737:chemistry* / Q000502:physiology*; D004789:Enzyme Activation; D004792:Enzyme Precursors / Q000737:chemistry*; D006458:Hemolymph / Q000737:chemistry; D015151:Immunoblotting; D019476:Insect Proteins; D007313:Insecta; D008077:Lipoproteins, LDL / Q000378:metabolism; D018402:Manduca; D016982:Micrococcus luteus / Q000378:metabolism; D008969:Molecular Sequence Data; D010457:Peptidoglycan / Q000737:chemistry; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D012697:Serine Endopeptidases / Q000737:chemistry*; D013997:Time Factors
D018076:DNA, Complementary; D004792:Enzyme Precursors; D019476:Insect Proteins; D008077:Lipoproteins, LDL; D010457:Peptidoglycan; D012333:RNA, Messenger; D011994:Recombinant Proteins; C038451:pro-phenoloxidase; D004156:Catechol Oxidase; D010450:Endopeptidases; C490363:hemolymph proteinase 14, Manduca sexta; D012697:Serine Endopeptidases; D003545:Cysteine