Coxiella burnetii, the causative agent of Q fever, is an intracellular bacterial pathogen. Studies on Coxiella have shown that a type IVB secretion system (T4BSS) contributes to the establishment of the infection by transferring protein molecules. In this report, we focus on two core proteins of the Coxiella T4BSS, namely the IcmG/DotF protein (CBU_1626) and the IcmK/DotH protein (CBU_1628). Here we present a method for the recombinant expression of IcmG and IcmK in E. coli. IcmG was purified by Strep-Tactin affinity chromatography and size exclusion chromatography, while for the purification of IcmK an additional anion exchange chromatography step was introduced. The yields of the purified IcmG and IcmK proteins were 1.2 mg/L and 3 mg/L, respectively. The purified proteins showed predominant band on SDS-PAGE gel of 37 kDa for the IcmG and 40 kDa for the IcmK. Protein folding is confirmed by circular dichroism spectroscopy. The dynamic light scattering experiment indicated that IcmG and IcmK existed in a homogenous form. Further Blue native PAGE indicates the presences of a monomeric form for the IcmK and IcmG. Our work lays the basis for functional exploration and structural determination of IcmG and IcmK proteins of Coxiella's secretion system.

Q热的病原体伯氏柯氏杆菌是一种细胞内细菌病原体。对Coxiella的研究表明，IVB 型分泌系统 (T4BSS) 通过转移蛋白质分子有助于建立感染。在本报告中，我们重点关注Coxiella T4BSS 的两种核心蛋白，即 IcmG/DotF 蛋白 (CBU_1626) 和 IcmK/DotH 蛋白 (CBU_1628)。在这里，我们提出了一种在大肠杆菌中重组表达 IcmG 和 IcmK 的方法. 通过 Strep-Tactin 亲和层析和尺寸排阻层析纯化 IcmG，而为了纯化 IcmK，引入了额外的阴离子交换层析步骤。纯化的 IcmG 和 IcmK 蛋白的产量分别为 1.2 mg/L 和 3 mg/L。纯化的蛋白质在 SDS-PAGE 凝胶上显示 IcmG 为 37 kDa 和 IcmK 为 40 kDa 的主要条带。蛋白质折叠由圆二色光谱证实。动态光散射实验表明IcmG和IcmK以同质形式存在。进一步的蓝色原生 PAGE 表明 IcmK 和 IcmG 存在单体形式。我们的工作为Coxiella分泌系统IcmG和IcmK蛋白的功能探索和结构测定奠定了基础。