Receptor-ligand binding in the cell-substrate contact zone: a quantitative analysis using CX3CR1 and CXCR1 chemokine receptors.
Receptor-ligand binding analyses have generally used soluble components to measure thermodynamic binding constants. In their biological context, adhesion receptors bind to an immobile ligand and the binding reaction is confined to the cell-substrate contact zone. We have developed a new procedure based on the spinning disk technology to measure the number of receptor-ligand bonds in the contact zone. Application of this methodology to the CX3CR1-fractalkine and the CXCR1-IL-8 receptor-ligand systems demonstrated that the level of binding to an immobilized ligand is reduced by several orders of magnitude in comparison to solution binding. A comparison of the solution binding and contact zone binding constants shows that the effect of ligand immobilization was similar for each system. In contrast, although the CXCR1-IL-8 bond had the higher affinity, the average bond strength was only 10% of that for the CX3CR1 bond. Because fractalkine can be expressed as a cell surface-bound protein, CX3CR1 has been proposed to function as an adhesion receptor. The higher bond strength suggests that the bond architecture has also evolved to serve an adhesion function.
Lee
Fang-Hua
FH
Department of Microbiology, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
Haskell
Christopher
C
Charo
Isreal F
IF
Boettiger
David
D
D000818:Animals; D000073883:CX3C Chemokine Receptor 1; D002448:Cell Adhesion; D002478:Cells, Cultured; D054428:Chemokine CX3CL1; D020523:Chemokines, CX3C / Q000378:metabolism*; D016209:Interleukin-8 / Q000378:metabolism*; D007700:Kinetics; D008024:Ligands; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D011485:Protein Binding; D019707:Receptors, Chemokine / Q000378:metabolism*; D023062:Receptors, Interleukin-8A / Q000378:metabolism*; D012996:Solutions
D000073883:CX3C Chemokine Receptor 1; D054428:Chemokine CX3CL1; D020523:Chemokines, CX3C; C515539:Cx3cl1 protein, mouse; C471885:Cx3cr1 protein, mouse; D016209:Interleukin-8; D008024:Ligands; D008565:Membrane Proteins; D019707:Receptors, Chemokine; D023062:Receptors, Interleukin-8A; D012996:Solutions