| Hepatitis B is the most fatal disease in the world and has serious impact on the lifeand health of human beings. At present, prevention is the most effective way tocontrol the prevalence of Hepatitis B. Hepatitis B cannot be effectively cured byantiviral agents. Anti-hepatitis B virus antibody is the new orientation for theprevention and therapy of hepatitis B. The research and application of antibody wasadvanced dramatically by the development of genetic engineering technology andstructure biology. Although, genetic engineering antibodies have better specificitythan natural antibodies, their research and applications are limited by heavy workloadand tedious operations. These disadvantages of genetic engineering antibodies aresupplemented by structure biology. The number, structure and affinity of antibodiescan be optimized through computer simulation technology.The objective of this project is to optimize the affinity of the hepatitis B surfaceantibody through computer simulation technology, and to test their affinity by biologyexperiments. Middle hepatitis B surface antigen (MHBs Ag) and the sequence ofantibody are studied through the bioinformatics methods. Then, the crystal structureswhich have higher homology and quality to them are found from the database. Afterthis, the homology modeling technology is used to build the3-D structure of theepitope of MHBs Ag, heavy chain and light chain which are based on structure of1WZ4,4JDT and4KMT respectively. The assembly way of heavy chain and lightchain in the crystal structure of1F11is used to build the3-D structure of antibody asreference. The complex structure of MHBs Ag epitope and antibody is predicted andoptimized by the steepest descent method and conjugate gradient method. Then,molecular docking technology is used to realize the protein-protein molecular dockingbetween the optimized epitope of MHBs Ag and structure of antibody. A spiral part ofthe MHBs Ag epitope in this combination mode set in the middle of the loop in heavychain and light chain, and the CDR3region of heavy chain is wrapped as much aspossible by the two spiral angle of MHBs Ag. The interaction between antigen andantibody is increased, and the antibody of antigen recognition is enhanced through this optimization. This result is conformed to previous literature.After moderate optimization of antigen-antibody complex structure, the structureof the interaction between them is analyzed. In this status, MHBs Ag can effectivelyembed in the middle of grooves which formed by CDR3region of heavy chain andlight chain of antibody, and fully contact with the region.8hydrogen bond interaction,1salt bridge interaction and1cationic‐π interaction are produced to stabilize thestructure of the complex. There are2main amino acids Arg30and Tyr32of the lightchain of antibody,4main amino acids Tyr32, Arg98, Gln108and Tyr109of the heavychain of the antibody, and8main amino acids Asn1, Ser2, Gln4, Phe5, His6, Tyr18,Gly22and Gly23of MHBs Ag epitope participated in the hydrogen bondinginteraction, the saturated mutations of Arg30, Ala50of light chain and Arg98of heavychain are formed to get the energy change map by calculating the energy of saturatedmutations. Then, the combinational mutations are formed between the three sites, andall of these sites are mutated to the amino acid residues of maximum combined energy.The activity assay shows that the affinity of optimized variants is much higher thanthe variants which are not optimized.To sum up, the structure optimization of hepatitis B surface antibody is realized bythe computer simulation technology. And, the affinity of optimized antibody isobviously improved which is validated through biological experiments. All of theexperiments results provide a foundation for the clinical application of humanizedhepatitis B surface antibody. |
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