KMID : 0578320200430121023
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Molecules and Cells 2020 Volume.43 No. 12 p.1023 ~ p.1034
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Moieties of Complement iC3b Recognized by the I-domain of Integrin ¥áX¥â2
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Choi Jeong-Suk
Buyannemekh Dolgorsuren Nham Sang-Uk
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Abstract
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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, ¥áM¥â2 and ¥áX¥â2, respectively. Although there is general agreement that iC3b binds to the ¥áM and ¥áX I-domains of the respective ¥â2-integrins, much less is known regarding the regions of iC3b contributing to the ¥áX I-domain binding. In this study, using recombinant ¥áX I-domain, as well as recombinant fragments of iC3b as candidate binding partners, we have identified two distinct binding moieties of iC3b for the ¥áX I-domain. They are the C3 convertase-generated N-terminal segment of the C3b ¥á¡¯- chain (¥á¡¯NT) and the factor I cleavage-generated N-terminal segment in the CUBf region of ¥á-chain. Additionally, we have found that the CUBf segment is a novel binding moiety of iC3b for the ¥áM I-domain. The CUBf segment shows about a 2-fold higher binding activity than the ¥á¡¯NT for ¥áX 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.
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KEYWORD
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binding sites, complement, iC3b, I-domain, integrins, protein-protein interactions, ¥áM¥â2, ¥áX¥â2
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