Complement factor H binds at two independent sites to C-reactive protein in acute phase concentrations.
Factor H (FH) regulates the activation of C3b in the alternative complement pathway, both in serum and at host cell surfaces. It is composed of 20 short complement regulator (SCR) domains. The Y402H polymorphism in FH is a risk factor for age-related macular degeneration. C-reactive protein (CRP) is an acute phase protein that binds Ca(2+). We established the FH-CRP interaction using improved analytical ultracentrifugation (AUC), surface plasmon resonance (SPR), and synchrotron x-ray scattering methods. Physiological FH and CRP concentrations were used in 137 mM NaCl and 2 mM Ca(2+), in which the occurrence of denatured CRP was avoided. In solution, AUC revealed FH-CRP binding. The FH-CRP interaction inhibited the formation of higher FH oligomers, indicating that CRP blocked FH dimerization sites at both SCR-6/8 and SCR-16/20. SPR confirmed the FH-CRP interaction and its NaCl concentration dependence upon using either immobilized FH or CRP. The SCR-1/5 fragment of FH did not bind to CRP. In order of increasing affinity, SCR-16/20, SCR-6/8 (His-402), and SCR-6/8 (Tyr-402) fragments bound to CRP. X-ray scattering showed that FH became more compact when binding to CRP, which is consistent with CRP binding at two different FH sites. We concluded that FH and CRP bind at elevated acute phase concentrations of CRP in physiological buffer. The SCR-16/20 site is novel and indicates the importance of the FH-CRP interaction for both age-related macular degeneration and atypical hemolytic uremic syndrome.
Department of Structural and Molecular Biology, Darwin Building, University College London, Gower Street, London WC1E 6BT, United Kingdom.
Azubuike I
AI
Okemefuna
Ruodan
R
Nan
Ami
A
Miller
Jayesh
J
Gor
Stephen J
SJ
Perkins
D000210:Acute-Phase Reaction / Q000235:genetics / Q000378:metabolism; D019943:Amino Acid Substitution / Q000502:physiology; D001665:Binding Sites / Q000235:genetics; D002097:C-Reactive Protein / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D002118:Calcium / Q000737:chemistry / Q000378:metabolism; D003179:Complement C3b / Q000235:genetics / Q000378:metabolism; D017242:Complement Factor H / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008268:Macular Degeneration / Q000235:genetics / Q000378:metabolism; D011110:Polymorphism, Genetic; D011485:Protein Binding / Q000235:genetics; D020836:Protein Structure, Quaternary / Q000235:genetics; D012307:Risk Factors; D012965:Sodium Chloride / Q000737:chemistry / Q000378:metabolism
D012965:Sodium Chloride; D003179:Complement C3b; D017242:Complement Factor H; D002097:C-Reactive Protein; D002118:Calcium