The Study Of Structure, Cytotoxicity And Key Point In The Aggregate Process Of A?42 Dimer

Objective:According to relevant authoritative statistics,the number of patients accounts for 6%of the world's population over 65 years old,and the incidence of Alzheimer's disease is increasing year by year and the growth rate is also increasing.In recent years,there has been increasing evidence that soluble A?protein oligomers distributed in cell membranes have significant cytotoxicity compared to senile plaques highly polymerized by A?protein.Therefore,refinement of the structural properties of A?oligomers,the interaction between oligomers and membranes,and the polymerization mechanism of oligomers are important for inhibiting the cytotoxicity of A?oligomers.Among them,A?42 dimer as the smallest polymerization unit of A?protein oligomer is also the smallest toxicity unit widely studied,clarifying the structural characteristics of A?42 dimer,interaction with membrane and polymerization mechanism will contribute to Alzheimer the proposed treatment plan.Method:1.The building of complex system.We first performed a 40 ns molecular dynamics simulation on a membrane composed of 128 DPPC molecules,and selected a bAlanced DPPC membrane structure as the initial membrane structure.The initial four dimers were ver tically inSerted into the DPPC membrane perpendicular to the surface of the membrane.The complex system is filled with SPC water molecules,and water molecules located in the hydrophobic region of the DPPC membrane are removed,and then an appropriate amount of Na+and CL-ions are added to the system to bAlance the chArge of the system.2.Molecular dynamic simulation.Before the formal simulation,the system needs to go through two bAlancing steps(NVT and NPT)to make the system cloSer to the real physiological environment.After experiencing the bAlance of NVT and NPT,the four systems were simulated for 400 ns,and the limiting forces imposed on all atoms were removed in the system during the simulation.Long-range electrostatic interactions within the system will be calculated by PME under periodic boundary conditions.3.Umbrella sampling.Taking the center of mass distance of the two chains of the dimer as the reaction coordinate,one of the chains is limited,and the other chain is applied with a traction force in the Y-axis direction,the pulling rate is 0.01 nm/ps,and the traction constant k=1000 kJ/mol/nm~2 until the dimer is completely arated.Each of system was set 32 windows,and the distance between the two adjacent windows set to 0.1-0.12 nm.Each window was simulated for 10 ns.Results:1.The characteristics of A?42 dimer secondary structure.The A?peptide can be divided into two parts,an N-terminal polar region and a C-terminal hydrophobic region.There are five regions with high degree of?sheet in the dimer 2NCB during the simulation,two regions are located in the N-terminal polar region,Compared with2NCB,the other three dimers also have three regions of high?-sheet folding in the C-terminal hydrophobic region,and the positions are similar.There is a significant difference in the N-terminal polar region.The three dimers CNNC,NCNC and NCCN show a significant low?-folding in the N-terminal polar region.2.Effect of A?42 dimer on membrane.By analyzing the APL and fluidity embedded in different dimer DPPC membranes,it was found that the four dimers have different degrees of damage to the membrane.2NCB has the greatest effect on cell membranes.Conclusions:1.Compared to CNNC,NCNC and NCCN,the?sheet of N-terminal is more stable in 2NCB2.The four dimers have different degrees of damage to the membrane.The destructive effect be caused by the?-sheet of the N-terminal of the dimer.3.The four dimers have different polymeric interface,and the dissociation paths are also different.There are three key points of aggregation were found His14,Phe20,and Ala43.