SPSB家族蛋白含有SPRY结构域和SOCS盒。项目申请人解析了SPSB2的晶体结构(Kuang, et al. J Mol Biol. 2009)，并率先阐明了SPSB1,2,4通过SPRY结构域与诱导型一氧化氮合酶(iNOS)结合而介导iNOS的泛素化和蛋白酶体降解；SPSB2基因敲除巨噬细胞中iNOS和一氧化氮(NO)增加并加速对利什曼原虫的杀灭(Kuang, et al. J Cell Biol. 2010)，提供了通过干预SPSB与iNOS相互作用来增强免疫细胞NO产生，促进杀灭病原微生物(如结核杆菌和疟疾)或癌细胞的全新思路。本课题将解析SPSB2-iNOS氨基端复合物结构，并通过基于片段的NMR筛选发现可以抑制SPSB-iNOS相互作用的分子先导结构。另一方面，SPSB3不与iNOS结合而其靶蛋白未知。本课题将鉴定SPSB3的特异结合序列和细胞内靶蛋白，从而揭示其生物学功能。

The SPRY domain-containing SOCS box proteins (SPSB1 to 4) are a family of four proteins that consist of a central SPRY domain and a C-terminal SOCS box. We have recently solved the crystal structure of SPSB2 (Kuang, et al. J Mol Biol. 2009), and have shown that SPSB1, 2, 4 are novel negative regulators of inducible nitric oxide synthase (iNOS); they bind to the N-terminus of iNOS via their SPRY domains and target iNOS for ubiquitination and proteasomal degradation. Activated SPSB2-deficient macrophages produced significantly more nitric oxide (NO) and had enhanced Leishmania killing compared to control macrophages (Kuang, et al. J Cell Biol. 2010). The aims of this project are to determine the structural basis for the SPSB2-iNOS interaction and develop small molecule inhibitors thereof through fragment-based approaches. Such molecules will enhance nitric oxide production and may have potential therapeutic applications in pathogen and cancer cell killing. On the other hand, SPSB3 does not interact with iNOS. In this project we will use phage display and affinity-column purification methods to identify the binding motif and cellular protein target of SPSB3.