Department of Physics, Concordia University, 7141 Sherbrooke Str. West, Montreal, Quebec H4B 1R6 Canada.
J Phys Chem B. 2012 Sep 27;116(38):11780-90. doi: 10.1021/jp308055r. Epub 2012 Sep 18.
Chlorophyll-protein complexes are ideal model systems for protein energy landscape research. Here pigments, used in optical spectroscopy experiments as sensitive probes to local dynamics, are built into protein by Nature (in a large variety of local environments; without extraneous chemical manipulations or genetic engineering). Distributions of the tunneling parameter, λ, and/or protein energy landscape barrier heights, V, have been determined for (the lowest energy state of) the CP43 core antenna complex of photosystem II. We demonstrate that spectral hole burning (SHB) and hole recovery (HR) measurements are capable of delivering important information on protein energy landscape properties and spectral diffusion mechanism details. In particular, we show that tunneling rather than barrier hopping is responsible for both persistent SHB and subsequent HR at 5-12 K, which allows us to estimate the md(2) parameter of the tunneling entities as ~1.0 × 10(-46) kg·m(2). The subdistributions of λ actually contributing to the nonsaturated spectral holes (and affecting their recovery) differ from the respective full true distributions. In the case of the full λ-distribution being uniform (or the barrier height distribution ~1/√V, a model which has been widely employed in theories of amorphous solids at low temperatures and in HR analysis), the difference is qualitative, with λ subdistributions probed in the HR experiments being highly asymmetrical, and barrier V subdistributions deviating significantly from ~1/√V. Thus, the distribution of λ for the protein energy landscape tier directly probed by SHB is likely Gaussian and not uniform. Additionally, a Gaussian distribution of barriers, with parameters incompatible with those of the landscape tier directly probed by SHB, contributes to the thermocycling results.
叶绿素-蛋白质复合物是研究蛋白质能量景观的理想模型系统。在这里，色素被用作局部动力学的敏感探针，被自然界（在各种局部环境中；没有额外的化学处理或基因工程）构建到蛋白质中。已经确定了光合作用系统 II 的 CP43 核心天线复合物（最低能量状态）的隧穿参数 λ 和/或蛋白质能量景观势垒高度 V 的分布。我们证明了光谱烧孔（SHB）和孔恢复（HR）测量能够提供有关蛋白质能量景观性质和光谱扩散机制细节的重要信息。特别是，我们表明，隧穿而不是势垒跳跃负责在 5-12 K 下持续 SHB 和随后的 HR，这使我们能够估计隧穿实体的 md(2)参数约为 1.0 × 10(-46) kg·m(2)。实际上，对未饱和光谱孔（并影响其恢复）有贡献的 λ 子分布与各自的全真实分布不同。在全 λ 分布均匀的情况下（或势垒高度分布为1/√V，这是低温非晶固体理论和 HR 分析中广泛采用的模型），差异是定性的，HR 实验中探测到的 λ 子分布高度不对称，势垒 V 子分布明显偏离1/√V。因此，直接通过 SHB 探测的蛋白质能量景观层的 λ 分布可能是高斯分布而不是均匀分布。此外，与直接通过 SHB 探测的景观层参数不兼容的势垒高斯分布也会对热循环结果产生影响。
