Molecular Dynamics Study On Mechanical Stability And Force Regulation Mechanism Of ?3 Integrin Cytoplasmic Tail/Talin F3 Domain

As an important force-sensitive protein on the platelet plasma membrane,?3 integrin transducts bidirectional membrane signals and plays a key role in platelet coagulation and hemostasis.In bidirectional membrane signals pathway,Talin binds?3 integrin and bridges Actin to conducts intracellular cytoskeletal contraction and extracellular blood flow shear stress through the mechanism of force-chemical coupling,promoting integrin activation and platelets coagulation.Therefore,the mechanical linkage of integrin and Talin as a bridge connecting extracellular ligands and intracellular cytoskeleton must have great mechanical stability to withstand intracellular and extracellular mechanical forces and transduct mechanical signals,in order to mediate platelet aggregation and spread.The binding of integrin tail and Talin is simple and the low-affinity.How it withstands and transducts all the forces from intracellular and extracellular is still a mystery.Previous studies focused on the force-dependent stochastic unfolding and refolding of Talin ROD domains making Talin as an effective force buffer.However,the mechanical stability of the integrin-Talin mechanical linkage,the integrin cytoplasmic tail binding with Talin F3 domain complex is unknown.Because of the traditional biological experimental cannot reflect the dynamic conformation and structural basis of protein molecules at the atomic level,herein we conduct molecular dynamics simulation?MD?to study the?3 integrin cytoplasmic tail membrane-distal portion with the Talin F3 domain complex??3/F3?conformational changes and mechanical stability in different mechanical microenvironments,to reveal the force-dependent mechanical stability mechanism and structural basis of?3/F3,and further to understand the process of platelet adhesion and aggregation mediated by Talin and?3 integrin.We setup the simulation system based on the?3/F3 crystal structure?PDB ID:1MK7?,and perform thermal equilibrium and constant velocity steer MD for the?3/F3 system;than conduct constant force steer MD for the responding force conformation conducting in constant velocity steer MD simulation first;analysis and compare the conformational stability and hydrogen bond network evolution under different simulation conditions to reveal the structural basis of the mechanical stability of?3/F3 under different external forces.We found that the deformation of Talin F3 domain hydrophobic pocket can effectively buffer the tensile force about 100 p N,and the force-dependent F3 deformation cooperates with the hydrogen bonds interaction in?3/F3 binding interface(especially the ASP⁷⁴⁰ with TRP³⁵⁹)can resist the steer force about 250 p N?The steer force obtained by simulation is different from the absolute value obtained by experiment?.Appropriate force can promote?3integrin interacting with Talin.At a constant force of less than 20-60 p N,the?3/F3 exhibits a catch bond,the dissociation probability decreases with increasing force,and the area of binding interface and the number of hydrogen bond gradually increase.In contrast,when the force is greater than 20-60 p N,it appears as a slip bond.ALA⁷⁴²,and ASN⁷⁴⁴,TYR⁷⁴⁷ and GLU⁷⁴⁹ residues bingding with their particular partners play a key role in the mechanical stability.The biphasic force-dependent interaction of?3 integrin cytoplasmic tail membrane-distal portion with Talin F3 and the force-dependent?3/F3 conformational change is the basis for?3/F3 maintaining stable and transducting intracellular cytoskeletal tension and extracellular blood flow shear stress,and to regulate platelet spreading and aggregation.The researches deepened our understanding of the structural basis of integrin/Talin-mediated platelet adhesion and aggregation,and provided structural informations and new ideas for the design of new antithrombotic drugs targeting the interaction of integrin with Talin.