Prophenoloxidase-activating proteinase-2 from hemolymph of Manduca sexta. A bacteria-inducible serine proteinase containing two clip domains.
Proteolytic activation of prophenoloxidase in insects is a component of the host defense system against invading pathogens and parasites. We have purified from hemolymph of the tobacco hornworm, Manduca sexta, a new serine proteinase that cleaves prophenoloxidase. This enzyme, designated prophenoloxidase-activating proteinase-2 (PAP-2), differs from another PAP, previously isolated from integuments of the same insect (PAP-1). PAP-2 contains two clip domains at its amino terminus and a catalytic domain at its carboxyl terminus, whereas PAP-1 has only one clip domain. Purified PAP-2 cleaved prophenoloxidase at Arg(51) but yielded a product that has little phenoloxidase activity. However, in the presence of two serine proteinase homologs, active phenoloxidase was generated at a much higher level, and it formed covalently linked, high molecular weight oligomers. The serine proteinase homologs associate with a bacteria-binding lectin in M. sexta hemolymph, indicating that they may be important for ensuring that the activation of prophenoloxidase occurs only in the vicinity of invading microorganisms. PAP-2 mRNA was not detected in naive larval fat body or hemocytes, but it became abundant in these tissues after the insects were injected with bacteria.
Jiang
Haobo
H
Department of Entomology and Plant Pathology, Oklahoma State University, Stillwater 74078, USA. haobo@okstate.edu
Wang
Yang
Y
Yu
Xiao-Qiang
XQ
Kanost
Michael R
MR
D000595:Amino Acid Sequence; D000818:Animals; D018407:Bacterial Physiological Phenomena; D001483:Base Sequence; D003001:Cloning, Molecular; D018076:DNA, Complementary; D004789:Enzyme Activation; D004790:Enzyme Induction; D006458:Hemolymph / Q000201:enzymology*; D018402:Manduca; D008969:Molecular Sequence Data; D000073718:Pancreatitis-Associated Proteins; D012697:Serine Endopeptidases / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
D018076:DNA, Complementary; D000073718:Pancreatitis-Associated Proteins; C000612141:REG3A protein, human; D012697:Serine Endopeptidases; C022435:prephenoloxidase-activating enzyme