Structural Basis for the Unusual Qy Red-Shift and Enhanced Thermostability of the LH1 Complex from Thermochromatium tepidum
Structural Basis for the Unusual Qy Red-Shift and Enhanced Thermostability of the LH1 Complex from Thermochromatium tepidum
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DOI：
10.1021/acs.biochem.6b00742
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发表时间：
2016-11-29
期刊：
影响因子：
2.9
通讯作者：
Wang-Otomet, Zheng-Yu
中科院分区：
文献类型：
--
作者：
Yu, Long-Jiang;Kawakami, Tomoaki;Wang-Otomet, Zheng-Yu
紫色光合细菌中的大多数核心捕光复合物（LH 1）在870-890 nm范围内显示Q（y）吸收带，而来自嗜热细菌Thermochromatium tepidum的LH 1在915 nm处显示具有增强的热稳定性的Q（y）吸收带。这些特性受Ca 2+离子的调节。用其它二价金属离子取代Ca ~（2+）会导致复合物的Q（y）带蓝移到880-890 nm，热稳定性降低。在最近发表了Ca结合的LH 1-反应中心（RC）络合物的结构[Niwa，S.，等人（2014）Nature SOS，228]，我们已经确定了Sr-和Ba-取代的LH 1-RC络合物的晶体结构，其中LH 1 Q（y）带在888 nm处。在LH 1配合物中鉴定出16个Sr ~（2+）和Ba ~（2+）离子。Sr 2+和Ba 2+都位于相同的位置，虽然接近，但明显不同于Ca 2+结合位点。取代引起的构象重排仅限于金属结合位点。与Ca-LH 1-RC复合物不同，只有α-多肽参与LH 1中的Sr和Ba配位。这些配合物之间的热稳定性的差异可以归因于由金属结合形成的网络的不同模式。Sr-和Ba-LH 1-RC复合物仅通过LH 1 α-多肽形成单环网络，与Ca-LH 1-RC复合物中由α-和β-多肽组成的双环网络形成对比。的结构信息的基础上，氢键，结构完整性，和电荷分布的综合效应被认为是影响的核心天线复合物的光谱特性。
While the majority of the core light-harvesting complexes (LH1) in purple photosynthetic bacteria exhibit a Q(y) absorption band in the range of 870-890 nm, LH1 from the thermophilic bacterium Thermochromatium tepidum displays the Q(y) band at 915 nm with an enhanced thermostability. These properties are regulated by Ca2+ ions. Substitution of the Ca2+ with other divalent metal ions results in a complex with the Q(y) band blue-shifted to 880-890 nm and a reduced thermostability. Following the recent publication of the structure of the Ca-bound LH1-reaction center (RC) complex [Niwa, S., et al. (2014) Nature SOS, 228], we have determined the crystal structures of the Sr- and Ba-substituted LH1-RC complexes with the LH1 Q(y) band at 888 nm. Sixteen Sr2+ and Ba2+ ions are identified in the LH1 complexes. Both Sr2+ and Ba2+ are located at the same positions, and these are clearly different from, though close to, the Ca2+-binding sites. Conformational rearrangement induced by the substitution is limited to the metal binding sites. Unlike the Ca-LH1-RC complex, only the a-polypeptides are involved in the Sr and Ba coordinations in LH1. The difference in the thermostability between these complexes can be attributed to the different patterns of the network formed by metal binding. The Sr- and Ba-LH1-RC complexes form a single-ring network by the LH1 alpha-polypeptides only, in contrast to the double-ring network composed of both alpha- and beta-polypeptides in the Ca-LH1-RC complex. On the basis of the structural information, a combined effect of hydrogen bonding, structural integrity, and charge distribution is considered to influence the spectral properties of the core antenna complex.