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KMID : 0578320070240020240
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Molecules and Cells
2007 Volume.24 No. 2 p.240 ~ p.246
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Identification of Critical Residues for Plasminogen Binding by the αX I-domain of the β2 integrin, αXβ2
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Gang Jong-Gyun
Choi Jeong-Suk
Lee Joo-Hee
Nham Sang-Uk
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Abstract
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The β2 integrins on leukocytes play important roles in cell adhesion, migration and phagocytosis. One of the β2 integrins, αXβ2 (CD11c/CD18), is known to bind ligands such as fibrinogen, Thy-1 and iC3b, but its function is not well characterized. To understand its biological roles, we attempted to identify novel ligands. The functional moiety of αXβ2, the αX I-domain, was found to bind plasminogen, the zymogen of plasmin, with moderate affinity (1.92 X 10-6 M) in the presence of Mg2+ or Mn2+. The βD-α5 loop of the αX I-domain proved to be responsible for binding, and lysine residues (Lys242, Lys243) in the loop were the most important for recognizing plasminogen. An excess amount of the lysine analog, 6-aminohexanoic acid, inhibited αX I-domain binding to plasminogen, indicating that binding is lysine-dependent. The results of this study indicate that leukocytes regulate plasminogen activation, and consequently plasmin activities, through an interaction with αXβ2 integrin.
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KEYWORD
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αXβ2, β2 Integrin, Binding, I-Domain, Plasminogen/Plasmin
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