N. Kairies et al., The 2.0-angstrom crystal structure of tachylectin 5A provides evidence forthe common origin of the innate immunity and the blood coagulation systems, P NAS US, 98(24), 2001, pp. 13519-13524
Citations number
31
Categorie Soggetti
Multidisciplinary
Journal title
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Because invertebrates lack an adaptive immune system, they had to evolve ef
fective intrinsic defense strategies against a variety of microbial pathoge
ns. This ancient form of host defense, the innate immunity, is present in a
ll multicellular organisms including humans. The innate immune system of th
e Japanese horseshoe crab Tachypleus tridentatus, serving as a model organi
sm, includes a hemolymph coagulation system, which participates both in def
ense against microbes and in hemostasis. Early work on the evolution of ver
tebrate fibrinogen suggested a common origin of the arthropod hemolymph coa
gulation and the vertebrate blood coagulation systems. However, this conjec
ture could not be verified by comparing the structures of coagulogen, the c
lotting protein of the horseshoe crab, and of mammalian fibrinogen. Here we
report the crystal structure of tachylectin 5A (TL5A), a nonself-recognizi
ng 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 eviden
ce of a common ancestor for the innate immunity and the blood coagulation s
ystems.