Chimeric CD46/DAF molecules reveal a cryptic functional role for SCR1 of DAF in regulating complement activation
D Christiansen1, B Loveland, P Kyriakou
1Immunité and Infections Virales, V.P.V., CNRS-UCBL UMR 5537, Faculté de Médecine Laennec, 69372 Cedex 08, Lyon, France.
Insights
Chimeric proteins combining CD46 and DAF domains reveal new insights into complement regulation. Specific domain combinations, particularly DAF SCR1, show unexpected functional roles in controlling complement activation.
Area of Science:
- Immunology
- Complement System Biology
Background:
- The human complement system is crucial for innate immunity but requires tight regulation to prevent self-damage.
- Membrane cofactor protein (CD46) and decay accelerating factor (DAF or CD55) are key regulators of complement activation.
- Understanding the specific functional domains of CD46 and DAF is essential for comprehending complement regulation.
Purpose of the Study:
- To investigate the functional roles of specific domains within CD46 and DAF in regulating human serum complement.
- To generate and characterize chimeric proteins combining domains from CD46 and DAF.
- To elucidate how different combinations of short consensus repeat (SCR) domains influence complement regulatory activity.
Main Methods:
- Generation of chimeric proteins by substituting specific SCR domains of CD46 with those of DAF (x3DAF, x4DAF, x3/4DAF, x1/2DAF).
- Assessment of regulatory activity following classical and alternative pathway activation by measuring C3b deposition.
- Utilizing SCR-specific antibodies to map functional domains responsible for alternative pathway regulation.
Main Results:
- CD46 SCR III substitution (x3DAF) showed modest activity, while CD46 SCR IV (x4DAF) and combined SCR III+IV (x3/4DAF) were highly efficient in classical pathway regulation.
- CD46 SCR I+II substitution (x1/2DAF) showed no classical pathway regulation but significant alternative pathway control.
- The x1/2DAF chimera's alternative pathway activity was mapped to DAF SCR 1, 2, and CD46 SCR III, highlighting a novel role for DAF SCR1.
Conclusions:
- Combinations of SCR domains from CD46 and DAF can yield functional complement regulatory molecules.
- A previously unrecognized functional role for DAF SCR1 in alternative pathway regulation has been identified.
- These findings contribute to a deeper understanding of complement system regulation and the structure-function relationships of its regulators.
Abstract:
Chimeric proteins using membrane cofactor (CD46) and decay accelerating factor (DAF or CD55) were generated to further investigate the functional domains involved in the regulation of human serum complement. Following activation of the classical pathway, the isolated substitution of CD46 SCR III (x3DAF) exhibited a modest regulatory activity comparable to that of CD46. The isolated substitution of CD46 SCR IV (x4DAF), and the combined CD46 SCR III+IV substitutions (x3/4DAF) were essentially as efficient as DAF. No regulation of C3b deposition was observed with the combined CD46 SCR I+II substitutions (x1/2DAF). When tested after activation of the alternative pathway, both the x3DAF and x3/4DAF chimeras failed to regulate C3b deposition, while the x4DAF chimera still displayed some activity. In contrast to that observed following classical pathway activation, the x1/2DAF chimera exhibited a similar efficiency to wild type CD46 and DAF in controlling C3b deposition. Using SCR specific antibodies, the regulatory activity of the x1/2DAF chimera against the alternative pathway was mapped to the first three distal SCR (i.e. DAF 1, DAF 2 and CD46 III). These data demonstrate that several combinations of SCR domains from two related complement regulators can result in functional molecules, and reveal a novel and cryptic functional role for DAF SCR1.
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