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Decay-accelerating factor must bind both components of the complement alternative pathway C3 convertase to mediate

Claire L Harris¹, David M Pettigrew, Susan M Lea

¹Department of Medical Biochemistry and Immunology, School of Medicine, Cardiff University, Cardiff, United Kingdom.

Journal of Immunology (Baltimore, Md. : 1950)

|December 22, 2006

Summary

Decay-accelerating factor (DAF) uses its SCR2 and SCR4 domains to interact with complement C3 convertase subunits Bb and C3b, respectively, to inhibit the complement cascade. This clarifies DAF

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Lighting Up the Pathways to Caspase Activation Using Bimolecular Fluorescence Complementation

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Published on: March 5, 2018

Area of Science:

Immunology
Biochemistry
Complement System

Background:

Decay-accelerating factor (DAF; CD55) is a key regulator of the complement cascade.
DAF inhibits complement by dissociating C3 convertase enzymes, crucial for amplification.
Previous work showed DAF interacts with the Bb subunit of the alternative pathway C3 convertase.

Purpose of the Study:

To dissect the specific interactions between DAF domains and complement C3 convertase subunits.
To elucidate the functional roles of different DAF short consensus repeat (SCR) domains in complement regulation.

Main Methods:

Surface plasmon resonance (SPR) was used to analyze binding kinetics.
Interactions between DAF domains (SCR2, SCR3, SCR4) and complement subunits (C3b, Bb) were investigated.
Functional assays assessed the decay-accelerating activity of DAF truncation mutants.

Main Results:

DAF's SCR2 domain binds specifically to the Bb subunit.
DAF's SCR4 domain interacts with the C3b subunit.
SCR3 does not directly interact with either Bb or C3b, contrary to previous hypotheses.

Conclusions:

DAF utilizes SCR2 and SCR4 for interaction with C3bBb, mediating complement inhibition.
SCR2-Bb interaction enhances DAF binding avidity to the convertase.
SCR4-C3b interaction directly drives decay acceleration, inhibiting the complement cascade.