Prediction Of Catch-slip Bond Transition Of Kindlin2/?3-integrin Via Steered Molecular Dynamics Simulation

In tumor immune microenvironment,?3 integrin signaling can plays different roles in different circumstances.The necessary condition for these functions is the activation of ?3(the transition from a low to a high affinity state).Kindlin proteins,which are indispensable in the process of integrin activation,directly interact with cytoplasmic tail of integrin and mediate the cell-extracellular matrix adhesion and signaling.Kindlin2(K2)is the most widely distributed member of the kindlin family and is ubiquitously expressed.Its complex structure with ?3 integrin has been resolved in recent years.Unlike talins,K2 cannot directly alter the conformation of the integrin transmembrane helix and fail to activate integrin alone.The underlying mechanism is unclear.The study of the force dissociation of the K2/?3-tail complx and the conformation stabilization under different mechanical micro-environments should be of great significance for the further understanding of the structural basis of its synergistically activation of integrin.To reveal the molecular dynamics mechanism of interaction between K2 and ?3-tail,we perform molecular dynamics(MD)simulations for this K2F3/?3 complex with a “ramp-clamp” mode.Two software packages,VMD for visualization and modeling and NAMD 2.13 for energy minimizations and MD simulations,were used here.During the equilibrium of complex,hydrogen interaction maintains the stability of the F3/?3.During the simulation of “force-ramp”(constant velocity)mode,the resistance of F3/?3 has different kinds of H-bond evolution processes,but it can still speculate that at least three pairs of important H-bonds(M612-N781,K613-N781,W615-F779 and E665-R785)play a major role in the resistance.Besides,the complex exhibits a variety of unfolding pathways against tension applications,which are mainly distinguished by the disruption of hydrogen-bonds between the F3 domain ?1/?2 helixes and ?1/?2 sheets.All these factors allow the F3/?3 to withstand a force of about 200 p N.The “force-clamp”(constant force)mode is used to simulate the continuous stress state of the complex in vivo.We found that the different phases of the composite force dissociation have different dissociation probabilities,which shows the “catch-slip bond”(biphasic forcedependent)characteristics.This mechanism depends on the various mechanical response of the intermolecular interaction residue pairs.Using MD simulation of a “ramp-clamp” mode,we showed the steady state of the K2F3/?3 complex under different tensile forces and observed the dynamic process of molecular interaction.A possible underlying biophysical mechanism is that,the dissociation of K2F3/?3 complex is regulated by a “catch-slip bond” mechanism.Under mechanical force induction,different intermolecular residue pairs have different effects on the binding affinity of complex.This study not only provides insights into the structural basis and mechanical regulation mechanisms of the kindlin/integrin interaction,in understanding in kindlin/integrin-related signaling in different cellular biological processes,but also provides new ideas for biotherapy strategy targeting ?3 integrin in the process of tumor immunity.