title: Associative and structural properties of the region of complement factor H encompassing the Tyr402His disease-related polymorphism and its interactions with heparin.
abstract: Factor H (FH) is a major complement control protein in serum. The seventh short complement regulator (SCR-7) domain of the 20 in FH is associated with age-related macular degeneration through a Tyr402His polymorphism. The recombinant SCR-6/8 domains containing either His402 or Tyr402 and their complexes with a heparin decasaccharide were studied by analytical ultracentrifugation and X-ray scattering. The sedimentation coefficient is concentration dependent, giving a value of 2.0 S at zero concentration and a frictional ratio f/f(o) of 1.2 for both allotypes. The His402 allotype showed a slightly greater self-association than the Tyr402 allotype, and small amounts of dimeric SCR-6/8 were found for both allotypes in 50 mM, 137 mM and 250 mM NaCl buffers. Sedimentation equilibrium data were interpreted in terms of a monomer-dimer equilibrium with a dissociation constant of 40 microM for the His402 form. The Guinier radius of gyration R(G) of 3.1-3.3 nm and the R(G)/R(O) ratio of 2.0-2.1 showed that SCR-6/8 is relatively extended in solution. The distance distribution function P(r) showed a maximum dimension of 10 nm, which is less than the length expected for a linear domain arrangement. The constrained scattering and sedimentation modelling of FH SCR-6/8 showed that bent SCR arrangements fit the data better than linear arrangements. Previously identified heparin-binding residues were exposed on the outside curvature of this bent domain structure. Heparin caused the formation of a more linear structure, possibly by binding to residues in the linker. It was concluded that the His402 allotype may self-associate more readily than the Tyr402 allotype, SCR-6/8 is partly responsible for the folded-back structure of intact FH, and SCR-6/8 changes conformation upon heparin binding.
authors.affiliation: Department of Biochemistry and Molecular Biology, Darwin Building, University College London, Gower Street, London WC1E 6BT, UK.
authors.forename: Anira N
authors.initials: AN
authors.lastname: Fernando
authors.forename: Patricia B
authors.initials: PB
authors.lastname: Furtado
authors.forename: Simon J
authors.initials: SJ
authors.lastname: Clark
authors.forename: Hannah E
authors.initials: HE
authors.lastname: Gilbert
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Day
authors.forename: Robert B
authors.initials: RB
authors.lastname: Sim
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Perkins
mesh_terms: D000595:Amino Acid Sequence; D017242:Complement Factor H / Q000737:chemistry*; D019281:Dimerization; D006493:Heparin / Q000378:metabolism*; D006639:Histidine / Q000737:chemistry*; D006801:Humans; D008268:Macular Degeneration / Q000235:genetics*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011110:Polymorphism, Genetic; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D012542:Scattering, Radiation; D013329:Structure-Activity Relationship; D014443:Tyrosine / Q000737:chemistry*; D014461:Ultracentrifugation; D014961:X-Ray Diffraction
chemical_list: D014443:Tyrosine; D006639:Histidine; D017242:Complement Factor H; D006493:Heparin