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Crystal Structure Analysis of the Bb segment of Factor B
Structural highlights
DiseaseCFAB_HUMAN Defects in CFB are a cause of susceptibility to hemolytic uremic syndrome atypical type 4 (AHUS4) [MIM:612924. An atypical form of hemolytic uremic syndrome. It is a complex genetic disease characterized by microangiopathic hemolytic anemia, thrombocytopenia, renal failure and absence of episodes of enterocolitis and diarrhea. In contrast to typical hemolytic uremic syndrome, atypical forms have a poorer prognosis, with higher death rates and frequent progression to end-stage renal disease. Note=Susceptibility to the development of atypical hemolytic uremic syndrome can be conferred by mutations in various components of or regulatory factors in the complement cascade system. Other genes may play a role in modifying the phenotype.[1] [2] FunctionCFAB_HUMAN Factor B which is part of the alternate pathway of the complement system is cleaved by factor D into 2 fragments: Ba and Bb. Bb, a serine protease, then combines with complement factor 3b to generate the C3 or C5 convertase. It has also been implicated in proliferation and differentiation of preactivated B-lymphocytes, rapid spreading of peripheral blood monocytes, stimulation of lymphocyte blastogenesis and lysis of erythrocytes. Ba inhibits the proliferation of preactivated B-lymphocytes. 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 PubMedThe C-terminal fragment, Bb, of factor B combines with C3b to form the pivotal C3-convertase, C3bBb, of alternative complement pathway. Bb consists of a von Willebrand factor type A (vWFA) domain that is structurally similar to the I domains of integrins and a serine protease (SP) domain that is in inactive conformation. The structure of the C3bBb complex would be important in deciphering the activation mechanism of the SP domain. However, C3bBb is labile and not amenable to X-ray diffraction studies. We engineered a disulfide bond in the vWFA domain of Bb homologous to that shown to lock I domains in active conformation. The crystal structures of Bb(C428-C435) and its inhibitor complexes reveal that the adoption of the "active" conformation by the vWFA domain is not sufficient to activate the C3-convertase catalytic apparatus and also provide insights into the possible mode of C3-convertase activation. Structural analysis of engineered Bb fragment of complement factor B: insights into the activation mechanism of the alternative pathway C3-convertase.,Ponnuraj K, Xu Y, Macon K, Moore D, Volanakis JE, Narayana SV Mol Cell. 2004 Apr 9;14(1):17-28. PMID:15068800[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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