Journal Article

The disease-protective complement factor H allotypic variant Ile62 shows increased binding affinity for C3b and enhanced cofactor activity

Agustín Tortajada, Tamara Montes, Rubén Martı́nez-Barricarte, B. Paul Morgan, Claire L. Harris and Santiago Rodríguez de Córdoba

in Human Molecular Genetics

Volume 18, issue 18, pages 3452-3461
Published in print September 2009 | ISSN: 0964-6906
Published online June 2009 | e-ISSN: 1460-2083 | DOI: http://dx.doi.org/10.1093/hmg/ddp289
The disease-protective complement factor H allotypic variant Ile62 shows increased binding affinity for C3b and enhanced cofactor activity

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Mutations and polymorphisms in the gene encoding factor H (CFH) have been associated with atypical haemolytic uraemic syndrome, dense deposit disease and age-related macular degeneration. The disease-predisposing CFH variants show a differential association with pathology that has been very useful to unravel critical events in the pathogenesis of one or other disease. In contrast, the factor H (fH)-Ile62 polymorphism confers strong protection to all three diseases. Using ELISA-based methods and surface plasmon resonance analyses, we show here that the protective fH-Ile62 variant binds more efficiently to C3b than fH-Val62 and competes better with factor B in proconvertase formation. Functional analyses demonstrate an increased cofactor activity for fH-Ile62 in the factor I-mediated cleavage of fluid phase and surface-bound C3b; however, the two fH variants show no differences in decay accelerating activity. From these data, we conclude that the protective effect of the fH-Ile62 variant is due to its better capacity to bind C3b, inhibit proconvertase formation and catalyze inactivation of fluid-phase and surface-bound C3b. This demonstration of the functional consequences of the fH-Ile62 polymorphism provides relevant insights into the complement regulatory activities of fH that will be useful in disease prediction and future development of effective therapeutics for disorders caused by complement dysregulation.

Journal Article.  6551 words.  Illustrated.

Subjects: Genetics and Genomics

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