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

【摘要】：植物因其含有豐富的營(yíng)養(yǎng)物質(zhì)和水分而成為眾多病原微生物覬覦的目標(biāo)。然而,植物與動(dòng)物不同,植物營(yíng)固著生活,無(wú)法從環(huán)境中逃離又不具有特化的免疫細(xì)胞、神經(jīng)系統(tǒng)以及體液循環(huán)系統(tǒng)。為了適應(yīng)周?chē)h(huán)境,植物逐漸進(jìn)化出以細(xì)胞為單位的應(yīng)答和交流系統(tǒng)。而植物免疫的第一道防線(xiàn)就是通過(guò)細(xì)胞質(zhì)膜定位的模式識(shí)別受體(PRR)識(shí)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(gè)模式識(shí)別受體,通過(guò)識(shí)別細(xì)菌鞭毛蛋白N端保守的22個(gè)氨基酸(flg22)而發(fā)揮重要的免疫作用。Flg22的結(jié)合會(huì)誘導(dǎo)FLS2和LRR-RK BAK1的異聚化,進(jìn)而起始免疫信號(hào)。目前,已有很多有關(guān)FLS2識(shí)別flg22的研究報(bào)導(dǎo),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(dǎo)的FLS2信號(hào)激活通路中的功能尚不清楚。本研究利用昆蟲(chóng)細(xì)胞分泌表達(dá)FLS2和BAK1的胞外區(qū),通過(guò)pull down實(shí)驗(yàn)和凝膠過(guò)濾層析體外重組了flg22誘導(dǎo)的FLS2-BAK1異源復(fù)合物,并解析FLS2-flg22-BAK1胞外區(qū)的晶體結(jié)構(gòu),闡明flg22誘導(dǎo)FLS2-BAK1異源二聚化的分子機(jī)制。FLS2通過(guò)其超螺旋結(jié)構(gòu)內(nèi)表面細(xì)長(zhǎng)的凹槽來(lái)識(shí)別flg22,BAK1與復(fù)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(méi)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(shí)別復(fù)合物中flg22的C端,生化和細(xì)胞實(shí)驗(yàn)證明BAK1對(duì)flg22 C末端的識(shí)別對(duì)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(hào)增強(qiáng)子。根據(jù)我們的工作,表明FLS2-flg22-BAK1異源復(fù)合物的形成是受體激活以及跨膜信號(hào)的分子開(kāi)關(guān)。由于BAK1可以與多個(gè)PRR或LRR-RK形成配體依賴(lài)的異源二聚體,本研究為理解和研究他們的激活機(jī)制提供了理論和方法依據(jù)。同時(shí),與生長(zhǎng)信號(hào)復(fù)合物BRI1-BL-BAK1的研究工作比較,我們提出植物細(xì)胞外pH的改變參與調(diào)解植物發(fā)育和免疫信號(hào)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(xué)位授予單位】：清華大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2015
【分類(lèi)號(hào)】：Q943.2

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1 孫亞?wèn)|;植物模式識(shí)別受體激酶FLS2配體識(shí)別及其激活機(jī)制研究[D];清華大學(xué);2015年

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本文編號(hào)：1846322