Hoffmann, R. A wiki for the life sciences where authorship matters. Nature Genetics (2008)

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McRae, J.L. et al.

McRae, Duthy, Griggs, Ormsby, Cowan, Cromer, McKinstry, Parker, Murphy, Gordon,

Human factor H-related protein 5 has cofactor activity, inhibits C3 convertase activity, binds heparin and C-reactive protein, and associates with lipoprotein.

Factor H-related protein 5 (FHR-5) is a recently discovered member of the factor H (fH)-related protein family. FHR proteins are structurally similar to the complement regulator fH, but their biological functions remain poorly defined. FHR-5 is synthesized in the liver and consists of 9 short consensus repeats (SCRs), which display various degrees of homology to those of fH and the other FHR proteins. FHR-5 colocalizes with complement deposits in vivo and binds C3b in vitro, suggesting a role in complement regulation or localization. The current study examined whether rFHR-5 exhibits properties similar to those of fH, including heparin binding, CRP binding, cofactor activity for the factor I-mediated degradation of C3b and decay acceleration of the C3 convertase. rFHR-5 bound heparin-BSA and heparin-agarose and a defined series of truncations expressed in Pichia pastoris localized the heparin-binding region to within SCRs 5-7. rFHR-5 bound CRP, and this binding was also localized to SCRs 5-7. FHR-5 inhibited alternative pathway C3 convertase activity in a fluid phase assay; however, dissociation of the convertase was not observed in a solid phase assay. rFHR-5 displayed factor I-dependent cofactor activity for C3b cleavage, although it was apparently less effective than fH. In addition, we demonstrate association of FHR-5 with high density lipid lipoprotein complexes in human plasma. These results demonstrate that FHR-5 shares properties of heparin and CRP binding and lipoprotein association with one or more of the other FHRs but is unique among this family of proteins in possessing independent complement-regulatory activity.[1]

References

Human factor H-related protein 5 has cofactor activity, inhibits C3 convertase activity, binds heparin and C-reactive protein, and associates with lipoprotein. McRae, J.L., Duthy, T.G., Griggs, K.M., Ormsby, R.J., Cowan, P.J., Cromer, B.A., McKinstry, W.J., Parker, M.W., Murphy, B.F., Gordon, D.L. J. Immunol. (2005) [Pubmed]

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