Sequence and topology of the CorA magnesium transport systems of Salmonella typhimurium and Escherichia coli. Identification of a new class of transport protein.
Sequence and topology of the CorA magnesium transport systems of Salmonella typhimurium and Escherichia coli. Identification of a new class of transport protein.
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发表时间：
1993-07
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通讯作者：
Ronald L. Smith;J. Banks;M. D. Snavely;M. Maguire
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作者：
Ronald L. Smith;J. Banks;M. D. Snavely;M. Maguire
鼠伤寒沙门氏菌和大肠杆菌的CorA Mg 2+转运系统介导Mg 2+的流入和流出。CorA基因座的产物足以介导Mg 2+内流，而未连接的CorBCD基因座的产物允许CorA除了内流之外还介导外流。序列分析表明，该S.菌和大肠coli CorA基因座。每个物种中的基因座由表达凝胶分子量为42 kDa的蛋白质的单个基因组成（S。typhimurium）和39 kDa（E.大肠杆菌）。这些蛋白质的预测氨基酸序列各自为316个氨基酸长，98%相同，并且与任何已知蛋白质缺乏同源性。虽然CorA是一个完整的膜蛋白的生化标准，其预测的氨基酸序列包含28%的带电氨基酸。在大肠杆菌中，CorA的膜定位依赖于Sec途径。杆菌亲水性分析预测两个足够长的C-末端疏水序列跨越膜双层。通过构建CorA的缺失衍生物并将其遗传融合到BlaM或LacZ盒来确定CorA的膜拓扑结构。这些杂合蛋白的酶活性表明CorA蛋白的N-末端235个氨基酸残基位于周质空间内，包括单个周质结构域。CorA的C-末端区域由三个跨膜片段组成，而不是由亲水性图所建议的两个，从而将C末端沉积在细胞质内。这种拓扑结构表明CorA作为低聚物起作用，因为三个膜环对于任何种类的膜孔或通道都很可能是不够的。它与已知蛋白质的同源性的缺乏及其拓扑结构表明CorA Mg 2+转运蛋白代表了一类新的膜转运系统。
The CorA Mg2+ transport systems of Salmonella typhimurium and Escherichia coli mediate both influx and efflux of Mg2+. The product of the CorA locus is sufficient for mediation of Mg2+ influx while product(s) of the unlinked CorBCD loci allow CorA to mediate efflux in addition to influx. The nucleotide sequences of the S. typhimurium and E. coli CorA loci have been determined. The locus in each species consists of a single gene expressing a protein with gel molecular masses of 42 kDa (S. typhimurium) and 39 kDa (E. coli). The predicted amino acid sequences of these proteins are each 316 amino acids in length, are 98% identical, and lack homology to any known protein. Although CorA is an integral membrane protein by biochemical criteria, its predicted amino acid sequence contains 28% charged amino acid. Membrane localization of CorA was shown to be dependent on the Sec pathway in E. coli. Hydropathy analysis predicts two C-terminal hydrophobic sequences of sufficient length to span the membrane bilayer. The membrane topology of CorA was determined by constructing deletion derivatives of CorA and genetically fusing them to BlaM or LacZ cassettes. The enzymatic activities of these hybrid proteins indicate that the N-terminal 235 amino acid residues of the CorA protein are located within the periplasmic space, comprising a single periplasmic domain. The C-terminal region of CorA is composed of three membrane-spanning segments rather than the two suggested by hydropathy plots, thus depositing the C terminus within the cytoplasm. This topology suggests that CorA functions as an oligomer since three membrane loops are most likely insufficient for any sort of membrane pore or channel. Its lack of homology to known proteins and its topology indicate that the CorA Mg2+ transporter represents a new class of membrane transport system.