Rare loss-of-function mutation in complement component C3 provides insight into molecular and pathophysiological
Georgia Sfyroera1, Daniel Ricklin1, Edimara S Reis1
1Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, PA 19104;
Journal of Immunology (Baltimore, Md. : 1950)
|February 26, 2015
Summary
A novel C3 gene mutation (M373T) was identified, causing a complete loss of alternative pathway complement activation. This discovery clarifies the molecular basis of C3 dysfunction and its varied clinical presentations.
Area of Science:
- Immunology
- Molecular Biology
- Genetics
Background:
- The complement system's central protein, C3, is crucial for immune responses.
- A hereditary C3 dysfunction affecting the alternative pathway (AP) was previously noted but lacked genetic and molecular explanation.
Purpose of the Study:
- To identify the genetic cause and molecular consequences of a hereditary C3 dysfunction.
- To elucidate the role of C3 in alternative pathway activation and its clinical relevance.
Main Methods:
- Genetic sequencing to pinpoint a point mutation in the C3 β-chain (c.1180T > C; p.Met(373)Thr).
- Functional assays to assess AP activity in patient plasma.
- Structural analysis and binding studies involving compstatin and C3b.
Main Results:
- The identified M373T mutation completely abolished AP activity, requiring normal C3 for reconstitution.
- The mutation impacts C3's macroglobulin domain 4, altering compstatin and C3b binding.
- C3 activation and opsonization were impaired by the M373T mutation.
Conclusions:
- This study reveals the molecular mechanism of a C3 loss-of-function mutation.
- Findings provide insights into C3 convertase function, C3's role in diverse clinical conditions, and implications for complement inhibition therapies.
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