The insect immune protein scolexin is a novel serine proteinase homolog.
Scolexin is a coagulation-provoking plasma protein induced in response to bacterial or viral infection of larval Manduca sexta, a large lepidopterous insect. Here we report the isolation and sequencing of two cDNA clones that code for scolexin isoforms sharing 80% sequence identity. The scolexin sequences have low but recognizable sequence similarity to members of the chymotrypsin family and represent a new subfamily of chymotrypsin-like serine proteinases. Comparison with known structures reveals the conservation of key catalytic residues and a possible specificity for small nonpolar residues. Most remarkable is the absence of a canonical activation peptide cleavage site. This suggests that the regulation of scolexin activity will involve a novel activation mechanism.
Finnerty
C M
CM
Boyce Thompson Institute for Plant Research, Cornell University, Ithaca, New York 14853, USA. cmf5@cornell.edu
Karplus
P A
PA
Granados
R R
RR
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D018076:DNA, Complementary; D006023:Glycoproteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006801:Humans; D006868:Hydrolysis; D019476:Insect Proteins / Q000737:chemistry* / Q000235:genetics; D008969:Molecular Sequence Data; D017386:Sequence Homology, Amino Acid; D012697:Serine Endopeptidases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
D018076:DNA, Complementary; D006023:Glycoproteins; D019476:Insect Proteins; D012697:Serine Endopeptidases; C119965:scolexin protein, Manduca sexta