Solution structure of a functionally active fragment of decay-accelerating factor.
The second and third modules of human decay accelerating factor (DAF) are necessary and sufficient to accelerate decay of the classical pathway (CP) convertase of complement. No structure of a mammalian protein with decay-accelerating activity has been available to date. We therefore determined the solution structure of DAF modules 2 and 3 (DAF approximately 2,3). Structure-guided analysis of 24 mutants identified likely contact points between DAF and the CP convertase. Three (R96, R69, and a residue in the vicinity of L171) lie on DAF approximately 2,3's concave face. A fourth, consisting of K127 and nearby R100, is on the opposite face. Regions of module 3 remote from the semiflexible 2-3 interface seem not to be involved in binding to the CP convertase. DAF thus seems to occupy a groove on the CP convertase such that both faces of DAF close to the 2-3 junction (including a positively charged region that encircles the protein at this point) interact simultaneously. Alternative pathway convertase interactions with DAF require additional regions of CCP 3 lying away from the 2-3 interface, consistent with the established additional requirement of module 4 for alternative pathway regulation.
Uhrinova
Stanislava
S
Edinburgh Protein Interaction Centre, University of Edinburgh, Edinburgh EH9 3JJ, Scotland.
Lin
Feng
F
Ball
Graeme
G
Bromek
Krystyna
K
Uhrin
Dusan
D
Medof
M Edward
ME
Barlow
Paul N
PN
D001665:Binding Sites; D018958:CD55 Antigens / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D050577:Complement C3-C5 Convertases / Q000378:metabolism; D006801:Humans; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D019906:Nuclear Magnetic Resonance, Biomolecular; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012996:Solutions; D055672:Static Electricity; D013816:Thermodynamics
D018958:CD55 Antigens; D010446:Peptide Fragments; D011994:Recombinant Proteins; D012996:Solutions; D050577:Complement C3-C5 Convertases