[DAF_HUMAN] This protein recognizes C4b and C3b fragments that condense with cell-surface hydroxyl or amino groups when nascent C4b and C3b are locally generated during C4 and c3 activation. Interaction of daf with cell-associated C4b and C3b polypeptides interferes with their ability to catalyze the conversion of C2 and factor B to enzymatically active C2a and Bb and thereby prevents the formation of C4b2a and C3bBb, the amplification convertases of the complement cascade.
Decay-accelerating factor (CD55), a regulator of the alternative and classical pathways of complement activation, is expressed on all serum-exposed cells. It is used by pathogens, including many enteroviruses and uropathogenic Escherichia coli, as a receptor prior to infection. We describe the x-ray structure of a pathogen-binding fragment of human CD55 at 1.7 A resolution containing two of the three domains required for regulation of human complement. We have used mutagenesis to map biological functions onto the molecule; decay-accelerating activity maps to a single face of the molecule, whereas bacterial and viral pathogens recognize a variety of different sites on CD55.
Mapping CD55 function. The structure of two pathogen-binding domains at 1.7 A.,Williams P, Chaudhry Y, Goodfellow IG, Billington J, Powell R, Spiller OB, Evans DJ, Lea S J Biol Chem. 2003 Mar 21;278(12):10691-6. Epub 2002 Dec 22. PMID:12499389
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↑ Ward T, Pipkin PA, Clarkson NA, Stone DM, Minor PD, Almond JW. Decay-accelerating factor CD55 is identified as the receptor for echovirus 7 using CELICS, a rapid immuno-focal cloning method. EMBO J. 1994 Nov 1;13(21):5070-4. PMID:7525274
↑ Williams P, Chaudhry Y, Goodfellow IG, Billington J, Powell R, Spiller OB, Evans DJ, Lea S. Mapping CD55 function. The structure of two pathogen-binding domains at 1.7 A. J Biol Chem. 2003 Mar 21;278(12):10691-6. Epub 2002 Dec 22. PMID:12499389 doi:http://dx.doi.org/10.1074/jbc.M212561200