本文選題：FLS2-flg22-BAK1 + 共受體　； 參考：《清華大學》2015年博士論文

【摘要】：植物因其含有豐富的營養(yǎng)物質(zhì)和水分而成為眾多病原微生物覬覦的目標。然而,植物與動物不同,植物營固著生活,無法從環(huán)境中逃離又不具有特化的免疫細胞、神經(jīng)系統(tǒng)以及體液循環(huán)系統(tǒng)。為了適應周圍環(huán)境,植物逐漸進化出以細胞為單位的應答和交流系統(tǒng)。而植物免疫的第一道防線就是通過細胞質(zhì)膜定位的模式識別受體(PRR)識別病原菌特異性的分子模式(PAMPs/DAMPs)。其中,LRR-RKs是PRR的主要成員。FLS2是典型的LRR-RK,也是模式生物擬南芥中發(fā)現(xiàn)的第一個模式識別受體,通過識別細菌鞭毛蛋白N端保守的22個氨基酸(flg22)而發(fā)揮重要的免疫作用。Flg22的結(jié)合會誘導FLS2和LRR-RK BAK1的異聚化,進而起始免疫信號。目前,已有很多有關(guān)FLS2識別flg22的研究報導,但缺乏相關(guān)的結(jié)構(gòu)信息。更重要的是,BAK1蛋白在flg22誘導的FLS2信號激活通路中的功能尚不清楚。本研究利用昆蟲細胞分泌表達FLS2和BAK1的胞外區(qū),通過pull down實驗和凝膠過濾層析體外重組了flg22誘導的FLS2-BAK1異源復合物,并解析FLS2-flg22-BAK1胞外區(qū)的晶體結(jié)構(gòu),闡明flg22誘導FLS2-BAK1異源二聚化的分子機制。FLS2通過其超螺旋結(jié)構(gòu)內(nèi)表面細長的凹槽來識別flg22,BAK1與復合物中FLS2的C端有廣泛直接的接觸面,并且Flg22的結(jié)合以及與BAK1的相互作用并沒有引起FLS2的構(gòu)象改變或寡聚化。除此之外,BAK1的N端帽子結(jié)構(gòu)特異性的識別復合物中flg22的C端,生化和細胞實驗證明BAK1對flg22 C末端的識別對于FLS2-BAK1異源二聚體的形成至關(guān)重要,揭示了BAK1的功能是作為FLS2共受體而非信號增強子。根據(jù)我們的工作,表明FLS2-flg22-BAK1異源復合物的形成是受體激活以及跨膜信號的分子開關(guān)。由于BAK1可以與多個PRR或LRR-RK形成配體依賴的異源二聚體,本研究為理解和研究他們的激活機制提供了理論和方法依據(jù)。同時,與生長信號復合物BRI1-BL-BAK1的研究工作比較,我們提出植物細胞外pH的改變參與調(diào)解植物發(fā)育和免疫信號之間的平衡。
[Abstract]:Plants are coveted by many pathogenic microorganisms because of their rich nutrients and moisture. However, plants are different from animals in that they are fixed in life and cannot escape from the environment without specialized immune cells, nervous systems, and humoral circulatory systems. In order to adapt to the surrounding environment, plants have evolved cellular response and communication systems. The first line of defense of plant immunity is the molecular pattern of PAMPs / DAMPs which recognizes pathogen specificity by the pattern recognition receptor (PRR) located on the cytoplasmic membrane. LRR-RKs is the main member of PRR. FLS2 is a typical LRR-RKand the first pattern recognition receptor found in Arabidopsis thaliana. By recognizing 22 conserved amino acids of bacterial flagellin, flg22), the binding of Flg22 can induce the heteropolymerization of FLS2 and LRR-RK BAK1 and initiate the immune signal. At present, there are a lot of research reports about FLS2 recognition flg22, but lack of relevant structure information. More importantly, the function of flg22-induced FLS2 signal activation pathway is unclear. In this study, the extracellular domains of FLS2 and BAK1 were secreted by insect cells. The heterologous complexes of FLS2-BAK1 induced by flg22 were recombined by pull down experiment and gel filtration chromatography in vitro, and the crystal structure of the extracellular domain of FLS2-flg22-BAK1 was analyzed. The molecular mechanism of FLS2-BAK1 heterodimerization induced by flg22. FLS2 recognizes the wide and direct contact surface between flg22 and the C terminal of FLS2 in the complex by means of thin and long grooves on the inner surface of the superhelix structure. The binding of Flg22 and its interaction with BAK1 did not result in conformation change or oligomerization of FLS2. In addition, the N-terminal cap of BAK1 recognized the C-terminal of flg22 specifically in the complex. Biochemical and cellular experiments showed that the recognition of flg22 C-terminal by BAK1 was very important for the formation of FLS2-BAK1 heterodimer. It is revealed that BAK1 functions as a FLS2 coreceptor rather than as a signal enhancer. According to our work, it is suggested that the formation of FLS2-flg22-BAK1 heterologous complexes is the molecular switch of receptor activation and transmembrane signal. Since BAK1 can form ligand-dependent heterodimers with multiple PRR or LRR-RK, this study provides a theoretical and methodological basis for understanding and studying their activation mechanisms. At the same time, compared with the study of growth signal complex (BRI1-BL-BAK1), we suggest that the change of extracellular pH in plants is involved in regulating the balance between plant development and immune signals.
【學位授予單位】：清華大學
【學位級別】：博士
【學位授予年份】：2015
【分類號】：Q943.2

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1 孫亞東;植物模式識別受體激酶FLS2配體識別及其激活機制研究[D];清華大學;2015年

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