期刊
EMBO JOURNAL
卷 26, 期 2, 页码 623-633出版社
NATURE PUBLISHING GROUP
DOI: 10.1038/sj.emboj.7601500
关键词
carbohydrate recognition; fibrinogen-like domain; innate immunity; N-acetyl group; X-ray crystallography
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 angstrom, respectively. Both domains have three-lobed structures with clefts separating the distal parts of the protomers. Ca2+ ions are found at sites homologous to those described for tachylectin 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.
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