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Author Spotlight: Development of a Method for Identifying Small Molecular Antagonists of β2 Integrin Activation
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Moieties of Complement iC3b Recognized by the I-domain of Integrin αXβ2

Jeongsuk Choi1, Dolgorsuren Buyannemekh1, Sang-Uk Nham2

  • 1Department of Biology, Kangwon National University, Chuncheon 24341, Korea.

Molecules and Cells
|December 29, 2020
PubMed

Complement fragment iC3b serves as a major opsonin for facilitating phagocytosis via its interaction with complement receptors CR3 and CR4, also known by their leukocyte integrin family names, αMβ2 and αXβ2, respectively. Although there is general agreement that iC3b binds to the αM and αX I-domains of the respective β2-integrins, much less is known regarding the regions of iC3b contributing to the αX I-domain binding. In this study, using recombinant αX I-domain, as well as recombinant fragments of iC3b as candidate binding partners, we have identified two distinct binding moieties of iC3b for the αX I-domain. They are the C3 convertase-generated N-terminal segment of the C3b α'- chain (α'NT) and the factor I cleavage-generated N-terminal segment in the CUBf region of α-chain. Additionally, we have found that the CUBf segment is a novel binding moiety of iC3b for the αM I-domain. The CUBf segment shows about a 2-fold higher binding activity than the α'NT for αX I-domain. We also have shown the involvement of crucial acidic residues on the iC3b side of the interface and basic residues on the I-domain side.

Keywords:
I-domainbinding sitescomplementiC3bintegrinsprotein-protein interactionsαMβ2αXβ2

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