Low spring constant regulates P-selectin-PSGL-1 bond rupture.

Forced dissociation of selectin-ligand bonds is crucial to such biological processes as leukocyte recruitment, thrombosis formation, and tumor metastasis. Although the bond rupture has been well known at high loading rate r(f) (>or=10(2) pN/s), defined as the product of spring constant k and retract velocity v, how the low r(f) (<10(2) pN/s) or the low k regulates the bond dissociation remains unclear. Here an optical trap assay was used to quantify the bond rupture at r(f) <or= 20 pN/s with low k ( approximately 10(-3)-10(-2) pN/nm) when P-selectin and P-selectin glycoprotein ligand 1 (PSGL-1) were respectively coupled onto two glass microbeads. Our data indicated that the bond rupture force f retained the similar values when r(f) increased up to 20 pN/s. It was also found that f varied with different combinations of k and v even at the same r(f). The most probable force, f*, was enhanced with the spring constant when k < 47.0 x 10(-3) pN/nm, indicating that the bond dissociation at low r(f) was spring constant dependent and that bond rupture force depended on both the loading rate and the mechanical compliance of force transducer. These results provide new insights into understanding the P-selectin glycoprotein ligand 1 bond dissociation at low r(f) or k.