Abstract: The purpose of this study was to analysis the antigenicity of msp4 protein of anaplamsa phagocytophilum. The informatics analysis was used to predict and analyze the important parameters of the msp4 protein, such as the physical and chemical properties, protein secondary structure, and its hydrophilicity, hydrophicity, bepipred linear epitope. According to the advantage epitope, we selected the high hydrophilic region of protein membrane outside domains, and cloned to pET32a prokaryotic expression vector. The bioinformatics analysis revealed that the msp4 protein was composed of 283 amino acids, and that its isoelectric point was 6.52. The msp4 protein was an stable hydropathilic protein（the instablility coefficient was 32.79, the grand average of hydropathicity was 0.063）. The secondary structure of the msp4 protein was mainly composed of random coils, extended strands, and alpha helixes. B cell epitope predicted that the msp4 protein has 14 linear epitopes. From the result of bioinformatics analysis, we selected the the 28-158 aa of the high hydrophilic region of protein membrane outside domains, and cloned to pET32a prokaryotic expression vector, the msp4 protein was successfully expressed and purified. The expressed and purified the recombinant msp4 protein lays a material foundation for the establishment of serological methods for anaplasma phaagocytophilum detection.

Key words: anaplasma phagocytophilum, bioinformatics analysis, msp4 protein, prokaryotic expression