Journal
JOURNAL OF BIOLOGICAL CHEMISTRY
Volume 278, Issue 6, Pages 3552-3561Publisher
AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
DOI: 10.1074/jbc.M205743200
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- NIGMS NIH HHS [GM58634, GM41247, R37 GM041247] Funding Source: Medline
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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.
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