Antigen Antibody Interaction Based On DNA Origami

The antigen antibody reaction is a crucial event of host defense pathogens,tumors and immunotherapy and in vitro disease detection.Antigen antibody reaction plays an important role in understanding the mechanism and behavior of the immune response and improves the level of detection and diagnosis of diseases.The epitopes of pathogens are mostly on their surface,and epitopes nanoscale distributions is closely related to the interaction of antibodies,which may be one of the main reasons for the difference of immune responses.However,it is a great challenge to control the distributions of epitopes on the surface at the nanoscale and quantitatively explain the behavior of antigen antibody reaction.DNA origami has extraordinary potential in the precise construction of nanostructures that has advantages of programming and simplicity.Particularly,its addressability provides an effective way to design,construct and control the spatial distributions of epitopes.Here,by combining DNA origami that has addressable and programmatic characteristics and single molecule detection techniques(atomic force microscope and single molecule fluorescence resonance energy transfer),we obtained high resolution images of single antibody with different morphologies by AFM,captured the dynamic process of antibody antigen reaction,and described the correlation between antibody neutralization and epitope distances at the single molecule level.This study provides insights for the quantitative elucidation of the molecular mechanism of antigen antibody reaction,the regulation of antigen antibody reaction efficiency,and related kinetic research.The specific research contents of this dissertation are as follows:The first part:Biomolecule distributions on DNA origami and its effects on molecular recognition.Typical two-dimensional DNA origami is about 100×100 nm~2,and whether the different distributions of nanoscale biomolecules on DNA origami have an impact on molecular reaction has been a concern at present.Here,by studying the biotin modified on the DNA origami,we found that binding efficiency of biotin and streptavidin reaction were significantly different at the edge of DNA origami and the central position of the surface,which provided guidance for the design of the epitopes in the subsequent antigen antibody reaction.The second part:High resolution imaging of antibodies.In liquid environment,high resolution imaging of single IgG is very difficult due to the small,soft,and the size and morphology of three domains of single IgG(two Fabs and one Fc)is similar.Here,by using the localized modification epitopes ability of DNA origami,the IgG was fixed on the DNA origami framework,and the high resolution images of single IgG molecules with different morphologies of"V","Y"and"T"were obtained,which provided new method for the study of antigen antibody reaction.The third part:The dynamic process of antigen antibody reaction.A single IgG contains two Fab domains that bind two antigens.Scientists speculated that the antibody binds to the antigen in two steps,first binding to one antigen and then binding to the other.Here,combining the positioning ability of DNA origami and the high speed atomic force microscopy,the antigen molecules were fixed to the DNA origami nanostructure through the self-assembly process of DNA origami,and then the dynamic process of binding between a single antibody and two adjacent antigens was obtained by using the real-time in situ imaging method.It provides detailed and direct experimental evidence for antigen and antibody reaction.The fourth part:Epitopes distributions effect on the ability of antibodies neutralization.Epitopes on the surface of various pathogens show different characteristics,including quantity and spatial distributions.Is there a simple strategy by which the pathogen can reduce antibodies neutralization thus decrease or evade the immune response?Here,DNA framework structures with different epitopes distributions were constructed by DNA origami,and the differences of binding reactions at different epitopes distances(3–20 nm)were studied.The experimental results showed that the binding efficiency of antigen and antibody changed with the change of the epitopes distance.When epitopes distance was about 10 nm,the binding efficiency was the highest.Through theoretical simulation analysis,it was found that the distance had the highest probability of antibody structure and the lowest potential.In addition,through the study of three different antigen antibody reaction,it was found that this phenomenon had certain universality.The results of this study may be helpful to study the ability of antibody neutralization and design vaccines.