2jhh
Structure of globular heads of M-ficolin at acidic pHStructure of globular heads of M-ficolin at acidic pH
Structural highlights
FunctionFCN1_HUMAN Complement-activating lectin and pattern recognition receptor. Binds GlcNAc. Binds preferentially to 9-O-acetylated 2-6-linked sialic acid derivatives and to various glycans containing sialic acid engaged in a 2-3 linkage.[1] Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedFicolins are soluble oligomeric proteins with lectin-like activity, assembled from collagen fibers prolonged by fibrinogen-like recognition domains. They act as innate immune sensors by recognizing conserved molecular markers exposed on microbial surfaces and thereby triggering effector mechanisms such as enhanced phagocytosis and inflammation. In humans, L- and H-ficolins have been characterized in plasma, whereas a third species, M-ficolin, is secreted by monocytes and macrophages. To decipher the molecular mechanisms underlying their recognition properties, we previously solved the structures of the recognition domains of L- and H-ficolins, in complex with various model ligands (Garlatti, V., Belloy, N., Martin, L., Lacroix, M., Matsushita, M., Endo, Y., Fujita, T., Fontecilla-Camps, J. C., Arlaud, G. J., Thielens, N. M., and Gaboriaud, C. (2007) EMBO J. 24, 623-633). We now report the ligand-bound crystal structures of the recognition domain of M-ficolin, determined at high resolution (1.75-1.8 A), which provides the first structural insights into its binding properties. Interaction with acetylated carbohydrates differs from the one previously described for L-ficolin. This study also reveals the structural determinants for binding to sialylated compounds, a property restricted to human M-ficolin and its mouse counterpart, ficolin B. Finally, comparison between the ligand-bound structures obtained at neutral pH and nonbinding conformations observed at pH 5.6 reveals how the ligand binding site is dislocated at acidic pH. This means that the binding function of M-ficolin is subject to a pH-sensitive conformational switch. Considering that the homologous ficolin B is found in the lysosomes of activated macrophages (Runza, V. L., Hehlgans, T., Echtenacher, B., Zahringer, U., Schwaeble, W. J., and Mannel, D. N. (2006) J. Endotoxin Res. 12, 120-126), we propose that this switch could play a physiological role in such acidic compartments. Structural basis for innate immune sensing by M-ficolin and its control by a pH-dependent conformational switch.,Garlatti V, Martin L, Gout E, Reiser JB, Fujita T, Arlaud GJ, Thielens NM, Gaboriaud C J Biol Chem. 2007 Dec 7;282(49):35814-20. Epub 2007 Sep 26. PMID:17897951[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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