Shelden Megan C, Howitt Susan M, Price G Dean
Molecular Plant Physiology Group, Research School of Biology, Australian National University, Canberra, ACT 0200, Australia.
Mol Membr Biol. 2010 Jan;27(1):12-22. doi: 10.3109/09687680903400120.
We have completed the first comprehensive transmembrane topology determination for a member of the ubiquitous and important SulP/SLC26 family of coupled anion transporters found in eukaryotes and prokaryotes. The prokaryotic member that we have mapped, namely BicA from Synechococcus PCC7002, is an important Na(+)-dependent bicarbonate transporter that is likely to play a major role in global primary productivity via the CO(2) concentrating mechanism in cyanobacteria. We experimentally determined the topology based on phoA-lacZ topology mapping combined with reference to a range of predictive models based on hydropathy analysis and positive charge distribution. The 12-TMH structure for BicA is characterized by tight turns between several pairs of TMH and it features a prominent cytoplasmically-located STAS domain that is characteristic of the SulP family. A key difference from previous predicted models is that we identify a cytoplasmic loop between helices 8 and 9 where previous models suggested a TMH. This region includes a highly conserved motif that defines the SulP family. The identification of this region as cytoplasmic, rather than transmembrane, has implications for the function and perhaps regulation of SulP family members. This finding is used to reinterpret mutagenesis data relating to highly conserved residues in this region from both plant and human SulP transporters.
我们已经完成了对真核生物和原核生物中普遍存在且重要的SulP/SLC26偶联阴离子转运蛋白家族成员的首个全面跨膜拓扑结构测定。我们绘制出拓扑结构的原核生物成员，即来自聚球藻PCC7002的BicA，是一种重要的Na⁺依赖性碳酸氢盐转运蛋白，它可能通过蓝细菌中的CO₂浓缩机制在全球初级生产力中发挥主要作用。我们通过phoA - lacZ拓扑图谱绘制，并参考一系列基于亲水性分析和正电荷分布的预测模型，通过实验确定了拓扑结构。BicA的12个跨膜螺旋（TMH）结构的特点是几对TMH之间有紧密的转角，并且具有一个位于细胞质中的突出的STAS结构域，这是SulP家族的特征。与之前的预测模型的一个关键区别在于，我们确定了螺旋8和9之间的一个细胞质环，而之前的模型认为这是一个TMH。该区域包含一个定义SulP家族的高度保守基序。将该区域确定为细胞质而非跨膜区域，对SulP家族成员的功能以及可能的调控具有重要意义。这一发现被用于重新解释来自植物和人类SulP转运蛋白该区域高度保守残基的诱变数据。
