The CbiB protein of Salmonella enterica is an integral membrane protein involved in the last step of the de novo corrin ring biosynthetic pathway.
The CbiB protein of Salmonella enterica is an integral membrane protein involved in the last step of the de novo corrin ring biosynthetic pathway.
复制标题
肠沙门氏菌的 CbiB 蛋白是一种整合膜蛋白，参与从头咕啉环生物合成途径的最后一步。
DOI：
10.1128/jb.01090-07
复制
发表时间：
2007
影响因子：
3.2
通讯作者：
Escalante-Semerena,JorgeC
中科院分区：
文献类型：
--
作者：
Zayas,CarmenL;Claas,Kathy;Escalante-Semerena,JorgeC
本文报道了鼠伤寒沙门氏菌LT2中腺苷钴胺素（辅酶B12）途径的最后一步，即腺苷钴酸（AdoCby）转化为腺苷钴酰胺-磷酸（adenosylcobinamide-phosphate）。先前的报道暗示了CbiB蛋白参与了这一途径的步骤。亲水性分析预测CbiB可能是一个完整的膜蛋白。我们利用计算机生成的CbiB一级序列拓扑模型来指导构建CbiB- lacz和CbiB- phoa蛋白融合体，用于探索CbiB在细胞膜中的一般拓扑结构。提出了一种改进的CbiB作为完整膜蛋白的模型。体内单氨基酸变化的影响分析表明，外周质和细胞质暴露的残基对CbiB功能至关重要。体内研究结果也表明，乙醇胺-磷酸（EA-P）是CbiB的底物，而丁- thrp不是，CbiB可能通过磷酸化激活AdoCby。后一种观察结果使我们认为CbiB是一种合成酶而不是合酶。质谱分析和生物分析结果表明，鼠伤寒血清型在EA-P为CbiB底物时可合成去钴胺素（缺乏C176甲基的钴胺素）。
We report results of studies of the conversion of adenosylcobyric acid (AdoCby) to adenosylcobinamide-phosphate, the last step of the de novo corrin ring biosynthetic branch of the adenosylcobalamin (coenzyme B12) pathway ofSalmonella entericaserovar Typhimurium LT2. Previous reports have implicated the CbiB protein in this step of the pathway. Hydropathy analysis predicted that CbiB would be an integral membrane protein. We used a computer-generated topology model of the primary sequence of CbiB to guide the construction of CbiB-LacZ and CbiB-PhoA protein fusions, which were used to explore the general topology of CbiB in the cell membrane. A refined model of CbiB as an integral membrane protein is presented. In vivo analyses of the effect of single-amino-acid changes showed that periplasm- and cytosol-exposed residues are critical for CbiB function. Results of in vivo studies also show that ethanolamine-phosphate (EA-P) is a substrate of CbiB, butl-Thr-P is not, and that CbiB likely activates AdoCby by phosphorylation. The latter observation leads us to suggest that CbiB is a synthetase not a synthase enzyme. Results from mass spectrometry and bioassay experiments indicate that serovar Typhimurium synthesizes norcobalamin (cobalamin lacking the methyl group at C176) when EA-P is the substrate of CbiB.