Journal
BIOPHYSICAL JOURNAL
Volume 103, Issue 4, Pages 777-785Publisher
CELL PRESS
DOI: 10.1016/j.bpj.2012.07.028
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Funding
- National Natural Science Foundation of China [30730032, 11072251, 10902117]
- National Key Basic Research Foundation of China [2011CB710904, 2006CB910303]
- Strategic Priority Research Program [XDA01030102, XDA04020219]
- Chinese Academy of Sciences [2005-1-16]
- National Institutes of Health [AI77343, HL090923, TW 05774-01]
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Binding of selectins to P-selectin glycoprotein ligand-1 (PSGL-1) mediates tethering and rolling of leukocytes on the endothelium during inflammation. Previous measurements obtained with a flow-chamber assay have shown that mutations of three tyrosines at the PSGL-1 N-terminus (Y46, Y48, and Y51) increase the reverse rates and their sensitivity to the force of bonds with P- and L-selectin. However, the effects of these mutations on the binding affinities and forward rates have not been studied. We quantified these effects by using an adhesion frequency assay to measure two-dimensional affinity and kinetic rates at zero force. Wild-type PSGL-1 has 2.2- to 8.5-fold higher binding affinities for P- and L-selectin than PSGL-1 mutants with two of three tyrosines substituted by phenylalanines, and 9.6- to 49-fold higher affinities than the PSGL-1 mutant with all three tyrosines replaced. In descending order, the affinity decreased from wild-type to Y48/51F, Y46/51F, Y46/48F, and Y46/48/51F. The affinity difference's were attributed to major changes in the forward rate and minor changes in the reverse rate, suggesting that these tyrosines regulate the accessibility of PSGL-1 to P- and L-selectin via electrostatic interactions, which is supported by molecular-dynamics simulations. Our results provide insights into the structure-function relationship of receptor-ligand binding at a single-residue level.
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