IV菌毛HCP是EHEC O157:H7重要的毒力因子，胶原纤维素ficolin 3是凝集素补体激活系统关键的补体分子，HCP与ficolin 3互作，对宿主补体系统起到抑制效应，但二者互作的精细结构和分子基础尚不清楚。本项目拟从三个方面阐释HCP与ficolin 3互作抑制补体激活系统的分子机制：（1）表达HCP和ficolin 3不同片段蛋白和氨基酸位点突变蛋白，研究HCP与ficolin 3互作对凝集素补体激活系统节点分子和受体表达的影响。（2）HCP与ficolin 3互作对MBL介导凝集素补体激活系统和经典补体激活系统的影响。（3）HCP与ficolin 3蛋白结晶和X射线检测，分析二者互作精细结构。本研究获得的结果和理论将深入诠释EHEC O157:H7的致病机制，并指导病原菌的有效防控。

HCP of IV pili is an important virulence factor of EHEC O157:H7 and ficolin 3 is one of key complement molecules. Interaction of HCP with ficolin 3 inhibits lectin complement activation system, but the molecular mechanism and fine structural basis between them is unclear. In this study, we will start research from three aspects to elucidate the mechanism. First of all, prepare segmental expression of HCP and ficolin 3 proteins and displaced key amino acid expression of HCP and ficolin 3 proteins to study effect on key complement moleculars and their receptors in lectin complement activation system. And, to study key protein changes in the signal cascades of MBL-mediated complement activation system and classical complement activation system. Finally, to study fine structure of HCP and ficolin 3 dimer using technology of protein crystallization and X-ray, in order to explain how HCP changes ficolin 3 structure and inhibits ficolin 3 role as a complement member. These results and theory obtained in this study will deepen interpretation of EHEC O157: H7 HCP pathogenesis and HCP-mediated immune escape mechanisms, further clear the interaction relationship between parasite of EHEC O157: H7 and host defense mechanisms.