Buyannemekh Dolgorsuren, Nham Sang-Uk
Divisions of Science Education and Biology, Kangwon National University, Chuncheon, Chuncheon 24341, Korea.
Mol Cells. 2017 May 31;40(5):355-362. doi: 10.14348/molcells.2017.0021. Epub 2017 May 24.
The β2 integrins are cell surface transmembrane proteins regulating leukocyte functions, such as adhesion and migration. Two members of β2 integrin, αMβ2 and αXβ2, share the leukocyte distribution profile and integrin αXβ2 is involved in antigen presentation in dendritic cells and transendothelial migration of monocytes and macrophages to atherosclerotic lesions. Receptor for advanced glycation end products (RAGE), a member of cell adhesion molecules, plays an important role in chronic inflammation and atherosclerosis. Although RAGE and αXβ2 play an important role in inflammatory response and the pathogenesis of atherosclerosis, the nature of their interaction and structure involved in the binding remain poorly defined. In this study, using I-domain as a ligand binding motif of αXβ2, we characterize the binding nature and the interacting moieties of αX I-domain and RAGE. Their binding requires divalent cations (Mg and Mn) and shows an affinity on the sub-micro molar level: the dissociation constant of αX I-domains binding to RAGE being 0.49 μM. Furthermore, the αX I-domains recognize the V-domain, but not the C1 and C2-domains of RAGE. The acidic amino acid substitutions on the ligand binding site of αX I-domain significantly reduce the I-domain binding activity to soluble RAGE and the alanine substitutions of basic amino acids on the flat surface of the V-domain prevent the V-domain binding to αX I-domain. In conclusion, the main mechanism of αX I-domain binding to RAGE is a charge interaction, in which the acidic moieties of αX I-domains, including E244, and D249, recognize the basic residues on the RAGE V-domain encompassing K39, K43, K44, R104, and K107.
β2整合素是调节白细胞功能（如黏附和迁移）的细胞表面跨膜蛋白。β2整合素的两个成员αMβ2和αXβ2具有相同的白细胞分布特征，并且整合素αXβ2参与树突状细胞中的抗原呈递以及单核细胞和巨噬细胞向动脉粥样硬化病变处的跨内皮迁移。晚期糖基化终产物受体（RAGE）是细胞黏附分子的一员，在慢性炎症和动脉粥样硬化中起重要作用。尽管RAGE和αXβ2在炎症反应和动脉粥样硬化发病机制中起重要作用，但它们相互作用的性质以及结合所涉及的结构仍不清楚。在本研究中，我们以I结构域作为αXβ2的配体结合基序，对αX I结构域与RAGE的结合性质及相互作用部分进行了表征。它们的结合需要二价阳离子（Mg和Mn），并且显示出亚微摩尔水平的亲和力：αX I结构域与RAGE结合的解离常数为0.49μM。此外，αX I结构域识别RAGE的V结构域，但不识别其C1和C2结构域。αX I结构域配体结合位点上的酸性氨基酸取代显著降低了I结构域与可溶性RAGE的结合活性，而V结构域平面上碱性氨基酸的丙氨酸取代则阻止了V结构域与αX I结构域的结合。总之，αX I结构域与RAGE结合的主要机制是电荷相互作用，其中αX I结构域的酸性部分（包括E244和D249）识别RAGE V结构域上包含K39、K43、K44、R104和K107的碱性残基。
