蓝细菌异形胞发育和模式形成的转录调控及其结构基础

Filamentous cyanobacterium Anabaena sp. PCC7120 is one of the dominant species of cyanobacteria in the lakes of fresh water. Due to the potency of differentiation from vegetative cells to regularly separated heterocysts, Anabaena is also an ideal model to study the cell differentiation and multiple-cell pattern formation. We have illustrated the structural basis of global transcriptional factor NtcA activated by the metabolite 2-OG, and systematically analyzed the mechanistic of another master regulator HetR recognized by its DNA targets and the inhibitory peptide PatS. However, a series of questions remain unanswered. For instance, how do NtcA, HetR and RNA polymerase cooperate, via their binding DNA sequences, to trigger the cell differentiation and to maintain the regular pattern? How do other transcriptional factors and enzymes participate and regulate the synthesis of specified cell wall of heterocysts? We will integrate the methodologies of microbiology, genetics, molecular biology, structural biology and enzymology, to systematically investigate structure and function of the super-macromolecular complex of NtcA, HetR and RNA polymerase, the master controller DevH for glycolipid synthesis and the transcriptional factor PatB for the maturation of heterocysts. The findings will provide us the structural insights into the concert regulation of heterocyst differentiation and pattern formation. Moreover, the investigations will give us some hints for understanding the mechanism of cell differentiation and regulation in the higher organisms.

丝状鱼腥蓝细菌(Anabaena sp. PCC7120)的一部分营养细胞具有分化为规则间隔的异形胞的潜能，是研究细胞分化和多细胞模式形成的理想模型。我们已阐明了在氮源缺乏时2-OG激活全局性转录因子NtcA的结构机理，并研究了NtcA下游控制异形胞分化的核心转录因子HetR识别DNA序列和抑制性寡肽PatS的分子机理。但是尚不清楚NtcA与HetR是如何相互作用并启动和维持异形胞的分化发育和间隔模式？其他转录因子和关键酶是如何调控异形胞特异性的糖脂层和多糖层的形成？我们将整合微生物遗传学、结构生物学和酶学的研究手段，对DNA介导的NtcA和HetR以及RNA聚合酶的超大复合物、糖脂层合成的总调控开关DevH以及控制异形胞成熟的转录因子PatB的结构和功能进行系统研究，以期阐明蓝细菌异形胞发育和模式形成的结构生物化学基础，并为研究高等生物的细胞分化和调控提供研究思路。

部分蓝细菌在氮源缺乏条件下能分化形成异形胞进行固氮作用。目前对于异形胞的分化以及异形胞特有的糖脂层、多糖层的形成乃至异形胞成熟的机制都知之甚少。我们以鱼腥蓝细菌Anabaena sp. PCC 7120为研究对象，系统地表达、纯化了一批参与蓝细菌异形胞分化和成熟的关键调节蛋白和酶类，并用X-射线晶体学手段解析了多个参与这一过程的蛋白质晶体结构。结合定点突变、酶活、微生物遗传学等多种手段，阐明了这些蛋白在参与蓝细菌异形胞形成过程中的分子机理，为更深入地研究蓝细菌异形胞的分化和成熟提供了结构生物学基础。