yybP-ykoY 孤儿核糖开关的锰离子（Mn²⁺）传感机制
Mn(2+)-sensing mechanisms of yybP-ykoY orphan riboswitches.
作者信息
Price Ian R, Gaballa Ahmed, Ding Fang, Helmann John D, Ke Ailong
机构信息
Department of Molecular Biology and Genetics, Cornell University, 253 Biotechnology Building, Ithaca, NY 14853, USA.
Department of Microbiology, Wing Hall, Cornell University, Ithaca, NY 14853, USA.
出版信息
Mol Cell. 2015 Mar 19;57(6):1110-1123. doi: 10.1016/j.molcel.2015.02.016.
Gene regulation in cis by riboswitches is prevalent in bacteria. The yybP-ykoY riboswitch family is quite widespread, yet its ligand and function remained unknown. Here, we characterize the Lactococcus lactis yybP-ykoY orphan riboswitch as a Mn(2+)-dependent transcription-ON riboswitch, with a ∼30-40 μM affinity for Mn(2+). We further determined its crystal structure at 2.7 Å to elucidate the metal sensing mechanism. The riboswitch resembles a hairpin, with two coaxially stacked helices tethered by a four-way junction and a tertiary docking interface. The Mn(2+)-sensing region, strategically located at the highly conserved docking interface, has two metal binding sites. Whereas one site tolerates the binding of either Mg(2+) or Mn(2+), the other site strongly prefers Mn(2+) due to a direct contact from the N7 of an invariable adenosine. Mutagenesis and a Mn(2+)-free E. coli yybP-ykoY structure further reveal that Mn(2+) binding is coupled with stabilization of the Mn(2+)-sensing region and the aptamer domain.
核糖开关在顺式作用中对基因的调控在细菌中很普遍。yybP-ykoY核糖开关家族分布广泛，但其配体和功能仍不清楚。在此，我们将乳酸乳球菌的yybP-ykoY孤儿核糖开关鉴定为一种依赖锰离子（Mn(2+)）的转录激活核糖开关，对Mn(2+)的亲和力约为30 - 40 μM。我们进一步确定了其2.7 Å分辨率的晶体结构，以阐明金属传感机制。该核糖开关类似一个发夹结构，有两个通过四环连接和三级对接界面同轴堆叠的螺旋。Mn(2+)传感区域位于高度保守的对接界面，有两个金属结合位点。其中一个位点可耐受镁离子（Mg(2+)）或Mn(2+)的结合，而另一个位点由于与一个不变腺苷的N7直接接触而强烈偏好Mn(2+)。诱变实验和不含Mn(2+)的大肠杆菌yybP-ykoY结构进一步表明，Mn(2+)的结合与Mn(2+)传感区域和适体结构域的稳定化相关联。
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