Institute of Complex Systems (ICS), ICS-6: Structural Biochemistry, Research Centre Jülich, 52425 Jülich, Germany.
Institute of Crystallography, University of Aachen (RWTH), Jägerstraße 17-19, 52056 Aachen, Germany.
Sci Rep. 2017 Feb 6;7:41811. doi: 10.1038/srep41811.
The complex of two membrane proteins, sensory rhodopsin II (NpSRII) with its cognate transducer (NpHtrII), mediates negative phototaxis in halobacteria N. pharaonis. Upon light activation NpSRII triggers a signal transduction chain homologous to the two-component system in eubacterial chemotaxis. Here we report on crystal structures of the ground and active M-state of the complex in the space group I222. We demonstrate that the relative orientation of symmetrical parts of the dimer is parallel ("U"-shaped) contrary to the gusset-like ("V"-shaped) form of the previously reported structures of the NpSRII/NpHtrII complex in the space group P222, although the structures of the monomers taken individually are nearly the same. Computer modeling of the HAMP domain in the obtained "V"- and "U"-shaped structures revealed that only the "U"-shaped conformation allows for tight interactions of the receptor with the HAMP domain. This is in line with existing data and supports biological relevance of the "U" shape in the ground state. We suggest that the "V"-shaped structure may correspond to the active state of the complex and transition from the "U" to the "V"-shape of the receptor-transducer complex can be involved in signal transduction from the receptor to the signaling domain of NpHtrII.
两种膜蛋白复合物，感觉视紫红质 II（NpSRII）与其同源转导蛋白（NpHtrII），介导嗜盐古菌 N. pharaonis 的负趋光性。光激活后，NpSRII 触发与真细菌趋化作用中的双组分系统同源的信号转导链。在这里，我们报道了复合物在 I222 空间群中的基态和活性 M 态的晶体结构。我们证明，与先前报道的 P222 空间群中 NpSRII/NpHtrII 复合物的结构相比，二聚体对称部分的相对取向是平行的（“U”形），而不是搭接样的（“V”形），尽管单独的单体结构几乎相同。在获得的“V”形和“U”形结构中 HAMP 结构域的计算机建模表明，只有“U”形构象才能允许受体与 HAMP 结构域紧密相互作用。这与现有数据一致，并支持在基态下“U”形的生物学相关性。我们建议“V”形结构可能对应于复合物的活性状态，并且从受体到 NpHtrII 的信号转导域的信号转导可能涉及受体-转导复合物从“U”到“V”形的转变。
