Single Molecule Study On The Conformational Transition Of DNA Caused By Histidine

As a basic genetic material in the organism,DNA affects the growth and development of organisms,which is also closely related to abnormal activities such as cell cancer and mutation.Many drugs used in clinic take DNA as the main target,damage its structure by acting with DNA and then influence the function of gene regulation and expression.The research results of DNA condensation for many years show that DNA condensation and charge inversion usually occur in solution of multivalent counterions.As one of the essential amino acids in the human body,histidine plays an important role in the process of DNA condensation and charge reversal.In this paper,histidine is used as the research object.Using single-molecule experimental methods,it was observed that polyhistidine can lead to DNA condensation and charge reversal.At the same time,the aggregation and charge neutralization behavior can be controlled by controlling the pH of the solution.First,the electrophoretic mobility of DNA was measured by dynamic light scattering experiments.The experimental results show: when the pH value is 7,the electrophoretic mobility of DNA is always negative and the charge reversal did not occur.And we lower the pH value,when the pH value is 5,the electrophoretic mobility of DNA will continue to increase with the increase of H8 concentration until the mobility is positive,and the charge reversal of DNA occurs.When the pH value is 3,the electrophoretic mobility of DNA will continue to increase with the increase of H8 concentration until the mobility is positive,and the charge reversal of DNA occurs.And the effect of charge reversal is even more pronounced.Next,the surface morphology of the DNA was observed using atomic force microscope.The experimental results show :when pH?7,keep the pH value constant,with the increase of Histidine concentration,the net charge of DNA is lower and lower after being compensated by positive valence ions in solution,Atomic force microscopy is observed in the image of the DNA coagulation more closely.When the concentration of histidine is fixed,the pH value is decreased and the degree of protonation of histidine is enhanced,DNA's imaging is also closer under the atomic force microscope.Finally,the tensile properties of DNA were measured with magnetic tweezers,the results further verify that histidine is able to make DNA concentration,and the decrease of pH value has played a further role in promoting the condensation of DNA.