Implications of the progressive self-association of wild-type human factor H for complement regulation and disease.
Factor H (FH) is a major regulator of complement alternative pathway activation. It is composed of 20 short complement regulator (SCR) domains and is genetically associated as a risk factor for age-related macular degeneration. Previous studies on FH suggested that it existed in monomeric and dimeric forms. Improved X-ray scattering and analytical ultracentrifugation methodology for wild-type FH permitted a clarification of these oligomeric properties. Data at lower concentrations revealed a dependence of the X-ray radius of gyration values on concentration that corresponded to the weak self-association of FH. Global sedimentation equilibrium fits indicated that a monomer-dimer equilibrium best described the data up to 1.3 mg/ml with a fitted dissociation constant K(D) of 28 microM and that higher oligomers formed at increased concentrations. The K(D) showed that about 85-95% of serum FH will be monomeric in the absence of other factors. Size-distribution analyses in sedimentation velocity experiments showed that monomeric FH was the major species but that as many as six oligomeric forms co-existed with it. The data were explained in terms of two weak dimerisation sites recently identified in the SCR-6/8 and SCR-16/20 fragments of FH with similar K(D) values. These observations indicate a mechanism for the progressive self-association of FH and may be relevant for complement regulation and the formation of drusen deposits that are associated with age-related macular degeneration.
Nan
Ruodan
R
Department of Biochemistry and Molecular Biology, Darwin Building, University College London, Gower Street, London WC1E 6BT, UK.
Gor
Jayesh
J
Perkins
Stephen J
SJ
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D001665:Binding Sites; D017242:Complement Factor H / Q000737:chemistry* / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism*; D019281:Dimerization; D005786:Gene Expression Regulation; D006463:Hemolytic-Uremic Syndrome / Q000209:etiology / Q000473:pathology; D006639:Histidine / Q000378:metabolism; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D008970:Molecular Weight; D015594:Optic Disk Drusen / Q000209:etiology / Q000473:pathology; D011110:Polymorphism, Genetic; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D012542:Scattering, Radiation; D017356:Synchrotrons; D014461:Ultracentrifugation; D014965:X-Rays
D006639:Histidine; D017242:Complement Factor H