Mechanical switching and coupling between two dissociation pathways in a P-selectin adhesion bond

Abstract

Many biomolecular bonds exhibit a mechanical strength that increases in proportion to the logarithm of the rate of force application. Consistent with exponential decrease in bond lifetime under rising force, this kinetically limited failure reflects dissociation along a single thermodynamic pathway impeded by a sharp free energy barrier. Using a sensitive force probe to test the leukocyte adhesion bond P-selectin glycoprotein ligand 1 (PSGL-1)-P-selectin, we observed a linear increase of bond strength with each 10-fold increase in the rate of force application from 300 to 30,000 pN͞sec, implying a single pathway for failure. However, the strength and lifetime of PSGL-1-P-selectin bonds dropped anomalously when loaded below 300 pN͞sec, demonstrating unexpectedly faster dissociation and a possible second pathway for failure. Remarkably, if first loaded by a ''jump'' in force to 20 -30 pN, the bonds became strong when subjected to a force ramp as slow as 30 pN͞sec and exhibited the same single-pathway kinetics under all force rates. Applied in this way, a new ''jump͞ramp'' mode of force spectroscopy was used to show that the PSGL-1-P-selectin bond behaves as a mechanochemical switch where force history selects between two dissociation pathways with markedly different properties. Furthermore, replacing PSGL-1 by variants of its 19-aa N terminus and by the crucial tetrasaccharide sialyl Lewis X produces dramatic changes in the failure kinetics, suggesting a structural basis for the two pathways. The two-pathway switch seems to provide a mechanism for the ''catch bond'' response observed recently with PSGL-1-P-selectin bonds subjected to smallconstant forces.N oncovalent interactions among large multidomain proteins underlie most adhesive functions in biology. Well known prototypes are the complexes formed between the selectin family of adhesion receptors, e.g., P-selectin expressed on activated endothelial cells or platelets, and their glycosylated ligands, e.g., the leukocyte mucin P-selectin glycoprotein ligand 1 (PSGL-1). Referred to as ''bonds,'' these interactions transiently interrupt rapid transport of leukocytes in blood flow and enable cells to perform a rolling exploration of vessel walls during the inflammatory response (1, 2). Most of our knowledge about how selectin bonds behave under stress has come from observing the decay in a number of receptor-bearing particles (cells or microspheres) tethered to walls by adhesive ligands in flow chambers. Held under nearly constant ''force clamp'' conditions, particles tethered by ligand͞selectin bonds release at progressively faster rates with increasing shear forces in high flow (3-5) but, at the same time, exhibit an unexpected shear threshold in slow flow below which particles also detach very quickly (6, 7). Recently tested by both flow chamber and atomic force microscope (AFM) techniques in a similar force clamp mode, the lifetimes of PSGL-1-P-selectin attachments were found to first increase with initial application of small forces before crossing over to de...

Single-molecule binding of CD44 to fibrin versus P-selectin predicts their distinct shear-dependent interactions in cancer

“…The P-selectin-PSGL-1 bond exhibits 'catch-slip' dissociation under force, in which bond lifetime is initially prolonged (catch) and then diminishes (slip) with increasing applied force (Evans et al, 2004;Marshall et al, 2003). The unstressed off-rate of P-selectin-PSGL-1 along the single pathway is 0.37±0.07 second -1 , whereas its reactive compliance is 0.23±0.01 nm, and displays a tensile strength of 70-150 pN for loading rates in the range of 300 to 30,000 pN/second, respectively (Evans et al, 2004). Comparison of the micromechanical properties of P-selectin binding to PSGL-1 relative to CD44v helps explain the more stable and slower rolling mediated by PSGL-1 compared with CD44 on P-selectin substrates in shear flow (McCarty et al, 2000).…”

Resolving the molecular mechanism of cadherin catch bond formation

“…These include energy landscapes with one bound state and two unbinding pathways 43 ; an energy landscape with two bound states, one of which is preferentially stabilized by force 44,45 ; bond dissociation along a multidimensional landscape where the direction of the tensile force and the reaction coordinate are misaligned [46][47][48] ; a freeenergy landscape with dynamic disorder that thermally fluctuates with time 49,50 ; and allosteric deformation models where external force changes the structure of the receptor either directly at the ligand-binding site 51 or at a distal location that ultimately propagates the deformation to the binding pocket [52][53][54][55] . Our simulations suggest that X-dimers form catch bonds via a slidingrebinding mechanism where a pulling force flexes the ectodomain and slides opposing EC1 domains resulting in the formation of de novo, force-induced H-bonds.…”

Deformation Model for Thioredoxin Catalysis of Disulfide Bond Dissociation by Force

“…We would like to emphasize that the description of the catch-slip anomaly proposed in the current work is not unique, and that several alternative models are available in the literature. 2,8,16,21,26,31 The current model differs from the alternative interpretations by its mathematical simplicity and by the bond deformation concept that is used to rationalize the physics of catchbinding.…”

“…The catch-slip binding transitions were discovered recently in a number of receptor-ligand biological complexes. 2,3,7,8,10,17,18,[21][22][23][24]26,27,32 The disulfide bond presents the first example of a chemical catch-bond, i.e., a system in which the increased lifetimes are associated with breaking a covalent bond.…”

“…The two-pathway description of the catch-slip behavior using a single bound state was first proposed in Pereverzev et al, 21 which focused on the anomalous force dependence of the measured lifetimes of the P,L-selectin/PSGL-1 bonds. 17,24 By containing an intermediate state the model of Wiita et al 30 belongs to the class of two-state models, 8,16,28 and therefore, it is more complex than model of reference. 21 Nevertheless, the Wiita model is very close to the two-pathway model 21 both conceptually and mathematically.…”