Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow 119234, Russia.
Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow 119234, Russia.
Biochem Biophys Res Commun. 2018 May 15;499(3):600-604. doi: 10.1016/j.bbrc.2018.03.196. Epub 2018 Mar 30.
Bacterial Na-transporting rhodopsins convert solar energy into transmembrane ion potential difference. Typically, they are strictly specific for Na, but some can additionally transport H. To determine the structural basis of cation promiscuity in Na-rhodopsins, we compared their primary structures and found a single position that harbors a cysteine in strictly specific Na-rhodopsins and a serine in the promiscuous Krokinobacter eikastus Na-rhodopsin (Kr2). A Cys253Ser variant of the strictly specific Dokdonia sp. PRO95 Na-rhodopsin (NaR) was indeed found to transport both Na and H in a light-dependent manner when expressed in retinal-producing Escherichia coli cells. The dual specificity of the NaR variant was confirmed by analysis of its photocycle, which revealed an acceleration of the cation-capture step by comparison with the wild-type NaR in a Na-deficient medium. The structural basis for the dependence of the Na/H specificity in Na-rhodopsin on residue 253 remains to be determined.
细菌 Na 转运视紫红质将太阳能转化为跨膜离子电势差。通常，它们严格特异性地针对 Na，但有些还可以运输 H。为了确定 Na 视紫红质中阳离子混杂的结构基础，我们比较了它们的一级结构，发现严格特异性 Na 视紫红质中的单一位置含有半胱氨酸，而混杂的 Krokinobacter eikastus Na 视紫红质（Kr2）中则含有丝氨酸。在视网膜产生的大肠杆菌细胞中表达时，确实发现严格特异性的 Dokdonia sp。PRO95 Na 视紫红质（NaR）的 Cys253Ser 变体以光依赖性方式同时运输 Na 和 H。NaR 变体的双重特异性通过其光循环分析得到证实，与 Na 缺乏培养基中的野生型 NaR 相比，该变体的阳离子捕获步骤得到了加速。Na 视紫红质中 Na/H 特异性对残基 253 的依赖性的结构基础仍有待确定。
