Identification of critical residues for plasminogen binding by the alphaX I-domain of the beta2 integrin, alphaXbeta2.
The beta2 integrins on leukocytes play important roles in cell adhesion, migration and phagocytosis. One of the beta2 integrins, alphaXbeta2 (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 alphaXbeta2, the alphaX I-domain, was found to bind plasminogen, the zymogen of plasmin, with moderate affinity (1.92 X 10-(6) M) in the presence of Mg(2+) or Mn(2+). The betaD-alpha5 loop of the alphaX I-domain proved to be responsible for binding, and lysine residues (Lys(242), Lys(243)) in the loop were the most important for recognizing plasminogen. An excess amount of the lysine analog, 6-aminohexanoic acid, inhibited alphaX 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 alphaXbeta2 integrin.
Gang
Jongyun
J
Division of Science Education and Biology, Research Institute of Life Sciences, Kangwon National University, Chuncheon 200-701, Korea.
Choi
Jeongsuk
J
Lee
Joo Hee
JH
Nham
Sang-Uk
SU
D000596:Amino Acids / Q000737:chemistry / Q000378:metabolism; D001665:Binding Sites; D018360:Crystallography, X-Ray; D006801:Humans; D016167:Integrin alphaXbeta2 / Q000737:chemistry* / Q000378:metabolism*; D007700:Kinetics; D008239:Lysine / Q000031:analogs & derivatives; D050505:Mutant Proteins / Q000378:metabolism; D010455:Peptides / Q000378:metabolism; D010958:Plasminogen / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013329:Structure-Activity Relationship; D020349:Surface Plasmon Resonance
D000596:Amino Acids; D016167:Integrin alphaXbeta2; D050505:Mutant Proteins; D010455:Peptides; D011993:Recombinant Fusion Proteins; D010958:Plasminogen; D008239:Lysine