Mutual relationships between structural and functional changes in a PsbM-deletion mutant of photosystem II
Mutual relationships between structural and functional changes in a PsbM-deletion mutant of photosystem II
复制标题
光系统 II PsbM 缺失突变体结构和功能变化之间的相互关系
DOI：
10.1039/c6fd00213g
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发表时间：
2017
影响因子：
3.4
通讯作者：
J.-R. Shenf and N. Kamiya
中科院分区：
文献类型：
--
作者：
S. Uto;K. Kawakami;Y. Umena;M. Iwai;M. Ikeuchi;J.-R. Shenf and N. Kamiya
光系统II （PSII）是一种膜蛋白复合体，它进行光诱导的电子转移和从水中析氧。PSII在其晶体形式中由19或20个亚基组成，并结合各种辅助因子，如叶绿素a、质体醌、类胡萝卜素和脂类。在初始光激发后，电荷分离产生一个电子，该电子转移到一个质体醌分子（QA）上，然后转移到另一个质体醌分子（QB）上。PsbM是具有一个跨膜螺旋的低分子量亚基，位于PSII二聚体的单体界面。基于先前的分辨率为4.2 Å的x射线晶体结构分析，已经报道了PsbM的功能是稳定PSII二聚体和维持PSII的电子转移效率。为了更详细地阐明PsbM的结构-功能关系，我们从长热聚球菌的PsbM缺失突变体（ΔPsbM-PSII）中改进了PSII晶体的质量，并成功地将衍射质量提高到2.2 Å。ΔPsbM-PSII的x射线晶体结构分析表明，PsbM亚基和邻近的类胡萝卜素和洗涤剂分子在单体-单体界面上没有电子密度。ΔPsbM-PSII的整体结构与野生型PSII相似，但由于PsbM的缺失，疏水跨膜亚基的排列发生了显著变化，导致涉及QB的脂质孔略微变宽。脂质空穴的扩大进一步诱导了与非血红素Fe（II）原子配位的碳酸氢盐离子的结构变化，并使远离PsbM位置的QB结合位点周围的多肽链不稳定。荧光衰减测量表明，与野生型PSII相比，ΔPsbM-PSII中QA到QB的电子传递速率降低。电子传递效率的功能变化完全基于PsbM亚基缺失引起的结构变化来解释。
Photosystem II (PSII) is a membrane protein complex that performs light-induced electron transfer and oxygen evolution from water. PSII consists of 19 or 20 subunits in its crystal form and binds various cofactors such as chlorophyll a, plastoquinone, carotenoid, and lipids. After initial light excitation, the charge separation produces an electron, which is transferred to a plastoquinone molecule (QA) and then to another plastoquinone (QB). PsbM is a low-molecular-weight subunit with one transmembrane helix, and is located in the monomer–monomer interface of the PSII dimer. The function of PsbM has been reported to be stabilization of the PSII dimer and maintenance of electron transfer efficiency of PSII based on previous X-ray crystal structure analysis at a resolution of 4.2 Å. In order to elucidate the structure–function relationships of PsbM in detail, we improved the quality of PSII crystals from a PsbM-deleted mutant (ΔPsbM-PSII) of Thermosynechococcus elongatus, and succeeded in improving the diffraction quality to a resolution of 2.2 Å. X-ray crystal structure analysis of ΔPsbM-PSII showed that electron densities for the PsbM subunit and neighboring carotenoid and detergent molecules were absent in the monomer–monomer interface. The overall structure of ΔPsbM-PSII was similar to wild-type PSII, but the arrangement of the hydrophobic transmembrane subunits was significantly changed by the deletion of PsbM, resulting in a slight widening of the lipid hole involving QB. The lipid hole-widening further induced structural changes of the bicarbonate ion coordinated to the non-heme Fe(II) atom and destabilized the polypeptide chains around the QB binding site located far from the position of PsbM. The fluorescence decay measurement indicated that the electron transfer rate from QA to QB was decreased in ΔPsbM-PSII compared with wild-type PSII. The functional change in electron transfer efficiency was fully interpreted based on structural changes caused by the deletion of the PsbM subunit.