本课题组利用家蚕杆状病毒表达系统组装成功AsiaI型FMDV空衣壳样颗粒，以此研制的复合型疫苗已获农业部临时生产文号。由于O型FMDV衣壳在酸性环境中更易解离，我们未能用此系统组装出空衣壳样颗粒。为解决该问题，我们拟对衣壳蛋白进行耐酸改造以提高其对酸性环境的耐受力。但目前尚未在O型FMDV衣壳蛋白上鉴定出可上调衣壳耐酸能力的关键位点。本项目在课题组已获得耐酸突变株的基础上开展这一关键分子位点的鉴定工作：依据突变株与母本病毒衣壳蛋白上的氨基酸差异，构建不同的感染性克隆分析相关位点的氨基酸替代现象与上调突变株耐酸能力的关系，以期从中鉴定出关键分子位点。在此基础上开展空衣壳样颗粒的分子构建工作，并分析相关位点改造对空衣壳样颗粒的耐酸能力、组装率及免疫原性的影响。研究结果有助于阐明FMDV适应酸性胁迫的分子机制，丰富对酸依赖性脱壳分子机制的认识，并为酸敏感性病毒空衣壳疫苗的研制提供新的方法和思路。

We have assembled empty capsid-like particles of serotype Asia I in silkworm larvae using silkworm-baculovirus expression system. Based on above research, we have developed the type O and Asia 1 bivalent vaccine (empty capsid vaccine compound) which composed of type O inactivated antigens and type Asia 1 empty capsid-like particles. It was licensed for use in eight provinces and autonomous regions of China in 2008. But we did not assembled empty capsid-like particles of serotype O in silkworm larvae or pupae. The empty capsid-like particles of type O are more difficult to obtain by genetic engineering techniques as the viral capsid of type O is more acid-sensitive than other types of FMDV. To overcome this problem, some amino acids in capsid protein will be replaced to improve acid resistance of empty capsid particles in this research. But the molecular determinants in viral capsid that mediate seotype O FMDV dissociation into pentameric subunits at acidic pH have not been elucidated. So we don't know which amino acids should be replaced. The infectious FMDV mutants with increased acid resistance were isolated by biological cloning after acid treatment in our proviously research. Based on these mutants, we will address the study to find the molecular determinants of viral resistance to acid-induced disassembly.The complete capsid coding regions of mutants and the parental virus will be sequenced and compared to find the nucleotide and amino acids replacements. The reversed genetics technique will be used to identify whether these amino acid replacements are sufficient to confer resistance to acid induced inactivation and find the molecular determinants finally. Based on above research, we will use the silkworm-baculovirus expression system to assemble the empty capsid-like particles of serotype O with an increased resistance to acid induced dissociation into pentameric subunits and evaluated the immunogenicity of these empty capsid-like particles. The results will not only provide a deeper insight into acid-dependent uncoating mechanism, but also provide an approach to develop the empty capsid-like particles vaccine for the acid-sensitive virus.