Institut für Theoretische Physik, Johannes Kepler Universität Linz, Altenberger Str. 69, 4040, Linz, Austria.
Photosynth Res. 2012 Mar;111(1-2):87-101. doi: 10.1007/s11120-011-9675-8. Epub 2011 Aug 2.
The linear optical spectra (absorbance, linear dichroism, circular dichroism, fluorescence) of the CP43 (PsbC) antenna of the photosystem II core complex (PSIIcc) pertaining to the S(0) → S(1) (Q(Y)) transitions of the chlorophyll (Chl) a pigments are simulated by applying a combined quantum chemical/electrostatic method to obtain excitonic couplings and local transition energies (site energies) on the basis of the 2.9 Å resolution crystal structure (Guskov et al., Nat Struct Mol Biol 16:334-342, 2009). The electrostatic calculations identify three Chls with low site energies (Chls 35, 37, and 45 in the nomenclature of Loll et al. (Nature 438:1040-1044, 2005). A refined simulation of experimental spectra of isolated CP43 suggests a modified set of site energies within 143 cm(-1) of the directly calculated values (root mean square deviation: 80 cm(-1)). In the refined set, energy sinks are at Chls 37, 43, and 45 in agreement with earlier fitting results (Raszewski and Renger, J Am Chem Soc 130:4431-4446, 2008). The present structure-based simulations reveal that a large part of the redshift of Chl 37 is due to a digalactosyldiacylglycerol lipid. This finding suggests a new role for lipids in PSIIcc, namely the tuning of optical spectra and the creation of an excitation energy funnel towards the reaction center. The analysis of electrostatic pigment-protein interactions is used to identify amino acid residues that are of potential interest for an experimental approach to an assignment of site energies and energy sinks by site-directed mutagenesis.
应用量子化学/静电组合方法，根据 2.9Å 分辨率的晶体结构（Guskov 等人，Nat Struct Mol Biol 16：334-342，2009），模拟了 PSIIcc 中 CP43（PsbC）天线的线性光学光谱（吸光度、线二色性、圆二色性、荧光），以获得叶绿素（Chl）a 色素的 Q(Y)）跃迁的 S(0)→S(1)（CP43（PsbC）天线的线性光学光谱（吸光度、线二色性、圆二色性、荧光））的激子耦合和局部跃迁能（局域能）。静电计算确定了三个局域能较低的 Chls（Loll 等人命名法中的 Chls 35、37 和 45）（Nature 438：1040-1044，2005）。对分离 CP43 的实验光谱的精细模拟表明，在直接计算值的 143cm(-1) 范围内，局域能有一个改进的集合（均方根偏差：80cm(-1)）。在改进的集合中，能量汇位于 Chls 37、43 和 45，与早期的拟合结果一致（Raszewski 和 Renger，J Am Chem Soc 130：4431-4446，2008）。基于结构的模拟表明，Chl 37 的红移很大一部分归因于二半乳糖基二酰基甘油脂质。这一发现表明，脂质在 PSIIcc 中具有新的作用，即调节光学光谱并为反应中心创建激发能量漏斗。静电色素-蛋白相互作用的分析用于识别氨基酸残基，这些残基可能对通过定点突变进行局域能和能量汇的实验分配具有潜在的兴趣。
