核苷酸切除修复通路能够修复紫外线和化疗药物引起的DNA损伤，该通路与着色性干皮症的发生及癌细胞对化疗药物的抗性直接相关。人XPA(着色性干皮症互补组A)-RPA(复制蛋白A)蛋白复合物参与核苷酸切除修复通路且在确认DNA损伤及招募下游核酸内切酶等方面起到关键作用。然而XPA-RPA复合物在DNA损伤位点附近的组装机制仍是未解之谜。本项目通过解析XPA-分支双链DNA复合物及XPA-RPA-分支双链DNA大型复合物的三维晶体结构，在原子分辨率水平上首次揭示XPA-RPA-DNA相互作用的机理及XPA-RPA复合物在DNA损伤位点附近的精细组装机制，阐明XPA-RPA复合物参与核苷酸切除修复通路的关键角色，探讨与疾病相关的XPA突变对其功能的影响。本项目能够为着色性干皮症的发病机理提供新的见解，也为潜在的针对阻断XPA-RPA相互作用的化疗增敏苗头化合物的理性设计和优化提供结构基础。

Nucleotide excision repair pathway is able to remove a wide range of DNA lesions caused by ultraviolet irradiation and chemotherapy drugs, and this pathway is directly related to the development of xeroderma pigmentosum and the resistance to chemotherapy drugs in cancer cells. Human XPA (xeroderma pigmentosum, complementation group A)-RPA (replication protein A) complex play significant roles in verifying DNA damage and recruiting downstream endonucleases to facilitate the repair of DNA lesions in nucleotide excision repair pathway. However, the mechanism of XPA-RPA complex assembling around the sites of DNA lesion in nucleotide excision repair pathway remains unclear. In this study, we plan to determine the three-dimensional crystal structure of XPA in complex with branched double-stranded DNA and the structure of multi-component complex containing XPA, RPA and branched double-stranded DNA. Based on these structures, the mechanism of XPA-RPA-DNA interaction will be revealed at the atomic level. Furthermore, we can depict the precise assembly mechanism of XPA-RPA complex around the sites of DNA lesion, demonstrate the crucial role of XPA-RPA complex in nucleotide excision repair pathway, and discuss the influences of disease-associated amino acid mutations on the biological functions of XPA. This study might provide a new insight into the pathogenic mechanism of xeroderma pigmentosum, and provide a potential structural basis for the rational design and optimization of the hits of chemotherapeutic sensitizers via blocking the interaction between XPA and RPA.