Conformational changes in mannan-binding lectin bound to ligand surfaces |
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Authors: | Dong Mingdong Xu Sailong Oliveira Cristiano L P Pedersen Jan S Thiel Steffen Besenbacher Flemming Vorup-Jensen Thomas |
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Affiliation: | Interdisciplinary Nanoscience Center (iNANO), Department of Physiucs and Astronomy, University of Aarhus, Aarhus C, Denmark. |
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Abstract: | The binding of soluble proteins to target surfaces is vital in triggering the immune response. However, structural insight into such processes is still lacking. Mannan-binding lectin (MBL) is a classic example of a pattern recognition molecule with important roles in innate immunity against microbial infections. By small angle x-ray scattering analysis we show that the large MBL complex in solution is folded into a ramified structure with a striking rotational symmetry and a structure permissive of elongation by unbending. Nevertheless, the structure in solution is found to be very stable. However, when the MBL molecule interacts with surface-immobilized ligands, the stable MBL structure is broken into a stretched state with separation of the ligand-binding domains as shown by high resolution atomic force microscopy. These studies provide a snapshot of the single molecule mechanics of MBL and the first direct evidence that the transition from the soluble state to surface-bound protein involves large conformational changes in the quaternary structure, thus highlighting the role of surface topography in immune recognition. |
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