Study On The Interaction Between DDAO And DNA By Single Molecule Technique

Understanding surfactant-DNA interactions is important for the development of basic physical biology and biomedical applications.In this study,the critical condensing force of DNA in dodecyldimethylamine oxide(DDAO)solution was investigated using the advanced biomolecule manipulation magnetic tweezers(MT)technology,which has potential implications for molecular manipulation of biomolecules such as proteins.DNA critical condensing force can be regulated by DDAO concentration and pH of solution and monovalent ion concentration(NaCl).First,at a fixed pH(7,5.5,4),the condensing force increases with the increasing of DDAO concentration.For example,when the pH of solution is 4 and the DDAO concentration is from 1 mm to 10 mM,the DNA critical condensing force increases from 0 pN to 4.6 pN approximately.Secondly,it was found that DDAO had no obvious effect on DNA under alkaline conditions,but it had condensing effect on DNA under acidic conditions.With the decrease of pH value of the solution,the condensing effect was enhanced.Finally,different concentrations of NaCl were added into DDAO-DNA solution,and it was found that the condensing effect of DNA became weaker with the increase of NaCl concentration DNA occurs decondensation.In addition,atomic force microscopy(AFM)and dynamic light scattering(DLS)experiments were used to investigate the influence of DDAO on DNA morphology and charge neutralization,and the change rule was consistent with that of MT.The three experimental methods proved that DDAO concentration and pH value were the factors of DNA condensation In neutral or alkaline solutions,the main attraction between DNA and DDAO was weak hydrophobic interaction,which could not induce DNA condensation.When the pH value of the system was lowered,there was hydrogen bonding between DDAO molecules besides electrostatic interaction and the DNA double helix structure was destroyed.DDAO concentration is lower,the surfactant molecules in the solution are monomers or dimers,acting as one or two basic charges,similar to monovalent or divalent cation.They can neutralize part of the negative charge of DNA,but can not induce DNA condensation.DDAO concentration increases with the formation of micelles,and DNA attracts more monomers,dimers and micelles,resulting in condensation.When-the DDAO concentration exceeds a certain critical value,most of the DDAO molecules in the solution form micelles,which are equivalent to polyvalent cations carrying a lot of positive charges.They can better neutralize the surface charge of DNA and have a stronger condensing effect.