全世界約有一半的人口感染了胃幽門桿菌，並且這株細菌與胃潰瘍和胃癌等疾病相關。雖然目前已經發現有許多因子對於細菌的感染所造成疾病很重要的，但是如何藉由調控基因表現改變這些因子功能的分子作用機制目前還不是很清楚。碳源調控蛋白, CsrA,是一種全面性調控蛋白，與生物膜的生成、細菌的游動能力、細菌鞭毛的合成等許多功能相關。為了了解CsrA在結構與功能是如何調控這些基因表現，以X-ray結晶學的方式研究CsrA蛋白質結構。從Escherichia coli大量表達CsrA重組蛋白，並且以親合性鎳離子螯合樹脂色層分析法與粒徑篩析層析法得到純度高的蛋白質，成功得到CsrA蛋白質結晶以及為了解出相位的硒甲硫氨酸化CsrA蛋白質結晶，並且收集了這些晶體的X光繞射數據。因為無法找出正確的晶格群 (space group)，所以沒有辦法正確的解出蛋白質結構。對於CsrA的功能研究，我們發現CsrA會與flaA的RNA結合，當精胺酸(arginine) 44這個位置的胺基酸突變成丙氨酸(alanine)後，CsrA幾乎失去了與RNA結合的能力,與野生株的胃幽門桿菌相比，其游動能力也明顯的下降。

To understand the structure-functional relationship of CsrA and the molecular mechanism by which CsrA exerts its function to regulate the gene expression, we aim to determine the crystal structure of CsrA by X-ray crystallography, SAXS, EMSA, and motility assay. We have purified CsrA and selenomethionyl CsrA protein, and get the crystals for X-ray diffraction data. But the structure of CsrA cannot be solved due to wrong space group. In the functional study of CsrA, CsrA can directly bind to flaA leader RNA, flaA1and flaA2. Residue Arg44 was involved in RNA recognition. The motility of csrA R44A mutant was significantly decreased by comparing with wild type H. pylori. In this study, CsrA can bind RNA by Arg44, and mutation of this site decrease bacteria motility.

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