Title : Structural insights into the innate immune recognition specificities of L- and H-ficolins
Abstract :
- Innate immunity relies critically upon the ability of a few pattern recognition molecules to sense molecular markers on pathogens, but little is known about these interactions at the atomic level
- Human L- and H-ficolins are soluble oligomeric defence proteins with lectin-like activity, assembled from collagen fibers prolonged by fibrinogen-like recognition domains
- The X-ray structures of their trimeric recognition domains , alone and in complex with various ligands, have been solved to resolutions up to 1.95 and 1.7 A, respectively
- Both domains have three-lobed structures with clefts separating the distal parts of the protomers
- Ca(2 +) ions are found at sites homologous to those described for tachy lectin 5A (TL5A), an invertebrate lectin
- Outer binding sites (S1) homologous to the GlcNAc-binding pocket of TL5A are present in the ficolins but show different structures and specificities
- In L-ficolin , three additional binding sites ( S2-S4 ) surround the cleft
- Together, they define an unpredicted continuous recognition surface able to sense various acetylated and neutral carbohydrate markers in the context of extended polysaccharides such as 1,3-beta-D-glucan, as found on microbial or apoptotic surfaces