2qfh

File:2qfh.jpg

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Solution Structure of the C-terminal SCR-16/20 fragment of Complement Factor H.

OverviewOverview

Factor H (FH) is a plasma glycoprotein that plays a central role in, regulation of the alternative pathway of complement. It is composed of 20, short complement regulator (SCR) domains. The SCR-1/5 fragment is required, for decay acceleration and cofactor activity, while the SCR-16/20 fragment, possesses binding sites for complement C3d and heparin. X-ray scattering, and analytical ultracentrifugation showed that SCR-1/5 was monomeric, while SCR-16/20 formed dimers. The Guinier radius of gyration R(G) of 4.3, nm for SCR-1/5 and those of 4.7 nm and about 7.8 nm for monomeric and, dimeric SCR-16/20, respectively, showed that their structures are, partially folded back and bent. The distance distribution function P(r), showed that SCR-1/5 has a maximum dimension of 15 nm while monomeric and, dimeric SCR-16/20 are 17 nm and about 27 nm long, respectively. The, sedimentation coefficient of 2.4 S for SCR-1/5 showed no, concentration-dependence, while that for SCR-16/20 was 2.8 S for the, monomer and 3.9 S for the dimer. Sedimentation equilibrium data showed, that SCR-1/5 is monomeric while SCR-16/20 exhibited a weak monomer-dimer, equilibrium with a dissociation constant of 16 microM. The constrained, scattering and sedimentation modelling of SCR-1/5 and SCR-16/20 showed, that partially folded-back and bent flexible SCR arrangements fitted both, data sets better than extended linear arrangements, and that the dimer was, best modelled in the SCR-16/20 model by an end-to-end association of two, SCR-20 domains. The SCR-1/5 and SCR-16/20 models were conformationally, similar to the previously determined partially folded-back structure for, intact wild-type FH, hence suggesting a partial explanation of the intact, FH structure. Comparison of the SCR-16/20 model with the crystal structure, of C3b clarified reasons for the distribution of mutations leading to, atypical haemolytic uraemic syndrome.

About this StructureAbout this Structure

2QFH is a Single protein structure of sequence from Homo sapiens. Full crystallographic information is available from OCA.

ReferenceReference

The regulatory SCR-1/5 and cell surface-binding SCR-16/20 fragments of factor H reveal partially folded-back solution structures and different self-associative properties., Okemefuna AI, Gilbert HE, Griggs KM, Ormsby RJ, Gordon DL, Perkins SJ, J Mol Biol. 2008 Jan 4;375(1):80-101. Epub 2007 Sep 14. PMID:18005991

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