1JC9: Tachylectin 5a From Tachypleus Tridentatus (Japanese Horseshoe Crab)

Because invertebrates lack an adaptive immune system, they had to evolve effective intrinsic defense strategies against a variety of microbial pathogens. This ancient form of host defense, the innate immunity, is present in all multicellular organisms including humans. The innate immune system of the Japanese horseshoe crab Tachypleus tridentatus, serving as a model organism, includes a hemolymph coagulation system, which participates both in defense against microbes and in hemostasis. Early work on the evolution of vertebrate fibrinogen suggested a common origin of the arthropod hemolymph coagulation and the vertebrate blood coagulation systems. However, this conjecture could not be verified by comparing the structures of coagulogen, the clotting protein of the horseshoe crab, and of mammalian fibrinogen. Here we report the crystal structure of tachylectin 5A (TL5A), a nonself-recognizing lectin from the hemolymph plasma of T. tridentatus. TL5A shares not only a common fold but also related functional sites with the gamma fragment of mammalian fibrinogen. Our observations provide the first structural evidence of a common ancestor for the innate immunity and the blood coagulation systems.
PDB ID: 1JC9Download
MMDB ID: 17982
PDB Deposition Date: 2001/6/8
Updated in MMDB: 2001/12
Experimental Method:
x-ray diffraction
Resolution: 2.01  Å
Source Organism:
Similar Structures:
Biological Unit for 1JC9: monomeric; determined by author
Molecular Components in 1JC9
Label Count Molecule
Protein (1 molecule)
Molecule annotation
Chemicals (2 molecules)
* Click molecule labels to explore molecular sequence information.

Citing MMDB