Molecular mechanism of spectral tuning in sensory rhodopsin II.
Molecular mechanism of spectral tuning in sensory rhodopsin II.
复制标题
感觉视紫红质 II 光谱调谐的分子机制。
DOI：
10.1021/bi0116487
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发表时间：
2001
期刊：
影响因子：
2.9
通讯作者：
Birge,RR
中科院分区：
文献类型：
--
作者：
Ren,L;Martin,CH;Wise,KJ;Gillespie,NB;Luecke,H;Lanyi,JK;Spudich,JL;Birge,RR
感觉视紫红质II(SRII)是古生菌视紫红质中独一无二的一种，其最大吸收波长接近500 nm，蓝移了约70 nm。此外，SRII在λ的最大吸收带显示出振动结构，而其他颜料则显示出完全展宽的最大吸收带。本文以纳氏纳氏杆菌感觉性视紫红质II(NpSRII)的2.4？晶体结构为参照，对这两种光物理性质的分子起源进行了研究。我们用半经验分子轨道理论(MOZYME)优化了生色团结合位内的生色团，用MNDO-PSDCI分子轨道理论计算了光谱性质。在MNDO-PSDCI SCF计算中，包括了生色团结合部位的整个第一壳，对于生色团π-体系，包括了完全的单、双构型相互作用。通过对细菌视紫红质(BR)1.55？晶体结构的相应计算的比较，我们确定了导致NpSRII光谱蓝移的主要分子机制和残基。我们得出结论，蓝移的主要来源与Arg-72(Arg-82在BR中)在两种蛋白质中的位置显著不同有关。在NpSRII中，这个侧链已经从发色团希夫碱氮转移到更接近β-亚硫叉环的位置。这种位置的移动将这种带正电荷的残基从BR中生色团失稳的区域转移到NpSRII中生色团稳定的区域，并负责大约一半的蓝移。其他重要的贡献者包括Asp-201、Thr-204、Tyr-174、Trp-76和W402，即水分子氢键合到希夫碱质子上。然而，W402的贡献是一种次要效应，可以追溯到Arg-72的移位。事实上，残基之间的二次相互作用对结合位点的性质有很大贡献。我们将NpSRII中振动结构的增加归因于Arg-72动态不均匀性的丧失和第二激发类1Ag*-态强度的增加，这现在在λ最大带轮廓中显示为一个单独的特征。在NpSRII中，强允许的类1Bu~(*+)态和高能的类1Ag~*-态高度混合，后者借用前者的强度来获得可观察到的振子强度。
Sensory rhodopsin II (SRII) is unique among the archaeal rhodopsins in having an absorption maximum near 500 nm, blue shifted roughly 70 nm from the other pigments. In addition, SRII displays vibronic structure in the λmaxabsorption band, whereas the other pigments display fully broadened band maxima. The molecular origins responsible for both photophysical properties are examined here with reference to the 2.4 Å crystal structure of sensory rhodopsin II (NpSRII) fromNatronobacterium pharaonis. We use semiempirical molecular orbital theory (MOZYME) to optimize the chromophore within the chromophore binding site, and MNDO-PSDCI molecular orbital theory to calculate the spectroscopic properties. The entire first shell of the chromophore binding site is included in the MNDO-PSDCI SCF calculation, and full single and double configuration interaction is included for the chromophore π-system. Through a comparison of corresponding calculations on the 1.55 Å crystal structure of bacteriorhodopsin (bR), we identify the principal molecular mechanisms, and residues, responsible for the spectral blue shift in NpSRII. We conclude that the major source of the blue shift is associated with the significantly different positions of Arg-72 (Arg-82 in bR) in the two proteins. In NpSRII, this side chain has moved away from the chromophore Schiff base nitrogen and closer to the β-ionylidene ring. This shift in position transfers this positively charged residue from a region of chromophore destabilization in bR to a region of chromophore stabilization in NpSRII, and is responsible for roughly half of the blue shift. Other important contributors include Asp-201, Thr-204, Tyr-174, Trp-76, and W402, the water molecule hydrogen bonded to the Schiff base proton. The W402 contribution, however, is a secondary effect that can be traced to the transposition of Arg-72. Indeed, secondary interactions among the residues contribute significantly to the properties of the binding site. We attribute the increased vibronic structure in NpSRII to the loss of Arg-72 dynamic inhomogeneity, and an increase in the intensity of the second excited1Ag*--like state, which now appears as a separate feature within the λmaxband profile. The strongly allowed1Bu*+-like state and the higher-energy1Ag*--like state are highly mixed in NpSRII, and the latter state borrows intensity from the former to achieve an observable oscillator strength.