Dipartimento di Chimica e Chimica Industriale, Università di Pisa, Via G. Moruzzi 13, 56124 Pisa, Italy.
Department of Physics, University of Pretoria, Lynnwood Road, Pretoria 0002, South Africa.
J Phys Chem Lett. 2024 Sep 26;15(38):9746-9756. doi: 10.1021/acs.jpclett.4c02005. Epub 2024 Sep 17.
Phycobilisomes (PBs) are giant antenna supercomplexes of cyanobacteria that use phycobilin pigments to capture sunlight and transfer the collected energy to membrane-bound photosystems. In the PB core, phycobilins are bound to particular allophycocyanin (APC) proteins. Some phycobilins are thought to be terminal emitters (TEs) with red-shifted fluorescence. However, the precise identification of TEs is still under debate. In this work, we employ multiscale quantum-mechanical calculations to disentangle the excitation energy landscape of PB cores. Using the recent atomistic PB structures from PCC 7002 and PCC 6803, we compute the spectral properties of different APC trimers and assign the low-energy pigments. We show that the excitation energy of APC phycobilins is determined by geometric and electrostatic factors and is tuned by the specific protein-protein interactions within the core. Our findings challenge the simple picture of a few red-shifted bilins in the PB core and instead suggest that the red-shifts are established by the entire TE-containing APC trimers. Our work provides a theoretical microscopic basis for the interpretation of energy migration and time-resolved spectroscopy in phycobilisomes.
藻胆体（PBs）是一种巨型天线超复合物，存在于蓝藻中，它利用藻胆素色素吸收阳光，并将收集到的能量传递到膜结合的光合作用系统。在 PB 核心中，藻胆素与特定的别藻蓝蛋白（APC）蛋白结合。一些藻胆素被认为是具有红移荧光的末端发射器（TEs）。然而，TEs 的精确鉴定仍存在争议。在这项工作中，我们采用多尺度量子力学计算来分解 PB 核心的激发能量景观。使用来自 PCC 7002 和 PCC 6803 的最近的原子 PB 结构，我们计算了不同 APC 三聚体的光谱性质，并分配了低能量的色素。我们表明，APC 藻胆素的激发能量取决于几何和静电因素，并通过核心内特定的蛋白-蛋白相互作用进行调节。我们的研究结果挑战了 PB 核心中少数几个红移双氢卟吩的简单图像，而是表明红移是由整个包含 TE 的 APC 三聚体建立的。我们的工作为藻胆体中的能量迁移和时间分辨光谱学的解释提供了理论微观基础。
