Limulus factor D, a 43-kDa protein isolated from horseshoe crab hemocytes, is a serine protease homologue with antimicrobial activity

FEBS Lett. 1996 Dec 2;398(2-3):146-50. doi: 10.1016/s0014-5793(96)01224-0.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Anti-Bacterial Agents / chemistry
  • Anti-Bacterial Agents / isolation & purification
  • Anti-Bacterial Agents / pharmacology*
  • Arthropod Proteins
  • Base Sequence
  • Blood Proteins / chemistry
  • Blood Proteins / genetics
  • Blood Proteins / isolation & purification
  • Blood Proteins / pharmacology*
  • DNA, Complementary / genetics
  • Enterobacteriaceae / drug effects*
  • Gene Library
  • Glycoproteins / chemistry
  • Glycoproteins / genetics
  • Glycoproteins / isolation & purification
  • Glycoproteins / pharmacology*
  • Hemocytes / chemistry*
  • Horseshoe Crabs / chemistry*
  • Humans
  • Microbial Sensitivity Tests
  • Molecular Sequence Data
  • Sequence Alignment
  • Serine Endopeptidases / chemistry
  • Serine Proteases


  • Anti-Bacterial Agents
  • Arthropod Proteins
  • Blood Proteins
  • DNA, Complementary
  • Glycoproteins
  • Serine Proteases
  • limulus factor D, Tachypleus tridentatus
  • Serine Endopeptidases

Associated data

  • GENBANK/D87214