期刊
NATURE STRUCTURAL & MOLECULAR BIOLOGY
卷 14, 期 3, 页码 224-228出版社
NATURE PUBLISHING GROUP
DOI: 10.1038/nsmb1210
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Factor B is the central protease of the complement system of immune defense. Here, we present the crystal structure of human factor B at 2.3-angstrom resolution, which reveals how the five-domain proenzyme is kept securely inactive. The canonical activation helix of the Von Willebrand factor A (VWA) domain is displaced by a helix from the preceding domain linker. The two helices conformationally link the scissile-activation peptide and the metal ion-dependent adhesion site required for binding of the ligand C3b. The data suggest that C3b binding displaces the three N-terminal control domains and reshuffles the two central helices. Reshuffling of the helices releases the scissile bond for final proteolytic activation and generates a new interface between the VWA domain and the serine protease domain. This allosteric mechanism is crucial for tight regulation of the complement-amplification step in the immune response.
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