Polymer Conjugation And Solution Behaviors Of Rod-Like Virus

Rod-like M13 virus has emerged as an attractive bionanomaterial due to its monodisperse size and can be tuned through chemical or genetic methods and self-assemble into assemblies with hierarchical structures.Polymer-bioconjuates synergistically combine the advantages of their individual constituents,which can lead to a wide range of potential biological and chemical applications.Furthermore,M13 has been proposed as a model system in soft condensed physics,especially,as a mesogenic unit in understanding the lyotropic liquid crystal(LC)theory of colloidal rods.Herein,we have created several kinds of polymer grafted M13 viruses and systemically investigated the influence of grafted polymer on the lyotropic LC phase and thermal stability of the virus,aim to obtain certain understanding of the origin of the cholesteric LC phases and regulate thermal stability of rod-like viruses.Firstly,this thesis successfully developed a simple and efficient method to graft the filamentous bacteriophages M13 with density PEG.Most importantly,the LC phase behavior of the densely grafted M13 can only form a pure nematic LC phase in the range of high ionic strengths or high concentrations.Combined with the scrutiny of several biophysical methods which sense different levels of structural changes of the major coat protein,we conclude that the secondary to tertiary structural change of the major coat protein of the virus,driven by the steric repulsion of the PEG brush may account for the nematic LC phase of the virus.Besides,in the whole ionic strength range,the I-N transition concentration of the densely grafted M13 virus is independent of the ionic strength.This is because the extended PEG layer on the surface of the virus fixs the effective diameter(Deff)of the virus.Secondly,two polymers(PEG and PNIPAM)were grafted onto the surface of M13 virus and their phase behaviors were investigated.The results indicated that when the concentration is above the I-N transition,the virus grafted with PEG,forms the chiral LC phase in the whole range of ionic strengths and concentrations.However,the PNIPAM grafted virus only forms the chiral LC phase in a small range of low ionic strengths and concentrations and out of this range,only forms a pure nematic LC phase.Combined with the structural change of the coat protein after polymer grafting,we think that the grafted PNIPAM chains start to collapse even at room temperature,which not only decrease Deff of the PNIPAM grafted virus,the collapsed polymers also form hydrophobic domains on the surface of the virus.Attractive interactions between the collapsed domains might lead to unwinding of the viruses into a pure nematic LC phase.Finally,we discussed the polymers conjugation on the thermal stability of rod-like M13 virus.Firstly,we studied the morphologies changes of the virus after heated to different temperature for different time.The results demonstrated that the morphologie of the PEG grated virus still could keep on its morphologies integrity after heated to 90°C,while most of the PNIPAM grafted virus broken into fragments.Secondly,we investigated the different levels of structural changes of the capsid protein with the increasing of temperature.The PEG conjugation could enhance the structure thermal stability of the protein.While PNIPAM decreased the thermal stability of the protein.Then the biological activity thermal stability of the virus was investigated.The results demonstrated that PEG can enhance the biological activity of the virus.It is because that the hydrophilic PEG is well water-soluble and could enhance the thermal stability of the virus.While with the increasing of the temperature,the PNIPAM could collapse into hydrophobic globule on the surface of the virus,and the attractive force between the adjacent globules enhanced the unwinding of the capsid protein,thus lead to the thermal stability of the virus decreased.