Limulus factor D, a 43-kDa protein isolated from horseshoe crab hemocytes, is a serine protease homologue with antimicrobial activity.
A glycoprotein (Mr = 43,000) from horseshoe crab hemocytes with antimicrobial activity against Gram-negative bacteria was purified. The internal peptide sequences coincided exactly with the deduced amino acid sequence of a cDNA clone, designated limulus factor D, which was isolated by screening a hemocyte cDNA library with an anti-human plasminogen antibody. The open reading frame codes for a precursor of factor D of 394 amino acid residues, including an NH2-terminal signal sequence. The COOH-terminal domain of factor D has significant sequence homology with the catalytic domain of mammalian serine proteases, in particular with human tissue plasminogen activator (32% identity), except for the substitution of Ser of the active site triad to Gly. Factor D has a unique NH2-terminal domain with weak sequence homology with part of the mammalian interleukin-6 receptor alpha-chain. Factor D is likely to have an important role in host defense mechanisms.
Kawabata
S
S
Department of Biology, Faculty of Science, Kyushu University, Fukuoka, Japan. skawascb@mbox.nc.kyushu-u.ac.jp
Tokunaga
F
F
Kugi
Y
Y
Motoyama
S
S
Miura
Y
Y
Hirata
M
M
Iwanaga
S
S
D000595:Amino Acid Sequence; D000818:Animals; D000900:Anti-Bacterial Agents / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology*; D060829:Arthropod Proteins; D001483:Base Sequence; D001798:Blood Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000494:pharmacology*; D018076:DNA, Complementary / Q000235:genetics; D004755:Enterobacteriaceae / Q000187:drug effects*; D015723:Gene Library; D006023:Glycoproteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000494:pharmacology*; D006434:Hemocytes / Q000737:chemistry*; D006737:Horseshoe Crabs / Q000737:chemistry*; D006801:Humans; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D016415:Sequence Alignment; D012697:Serine Endopeptidases / Q000737:chemistry; D057057:Serine Proteases
D000900:Anti-Bacterial Agents; D060829:Arthropod Proteins; D001798:Blood Proteins; D018076:DNA, Complementary; D006023:Glycoproteins; D057057:Serine Proteases; C103259:limulus factor D, Tachypleus tridentatus; D012697:Serine Endopeptidases