PSI–LHCI 超級複合體之光捕捉動力學的理論研究

Abstract

光系統 I–光捕捉複合體 I（Photosystem I-light-harvesting complex I，PSI-LHCI）儘管具有龐大的系統尺寸與顯著的結構異質性，仍可達到近乎單位的量子產率。雖然 PSI 核心天線中的激發能量傳遞（excitation energy transfer, EET）動力學已受到廣泛研究，但整個 PSI-LHCI 超級複合體中的能量傳遞動力學行為仍未被充分釐清。本研究以豌豆（Pisum sativum）之 PSI-LHCI 為對象，在靜態無序條件下探討其主導性的激發能量傳遞動力學特徵。

本研究首先對一個依量子產率分布之中位數選取的代表性無序實現，應用圖論中的最小割（minimum-cut）方法，建構一個最佳化的 14 群集粗粒化動力學模型，該模型可忠實重現完整系統的佔據數動力學。相同的粗粒化分析亦進一步套用於涵蓋不同量子產率百分位的其他無序實現，以及透過對整體無序系綜進行共識分群（consensus clustering）所獲得的無序平均模型。

在所有情況下，所得的粗粒化描述皆一致揭示：由外圍 LHCI 天線向 PSI 核心的激發能量傳遞呈現穩健的雙分支（two-branch）機制。此動力學架構具有三項關鍵特徵：分支內能量轉移迅速、兩分支之間的直接交換極少，以及一個反覆出現的中心橋接叢集，其扮演控制激發能否進入反應中心（reaction center, RC）的關鍵閘門。這套一致的雙分支動力學圖像顯示，PSI-LHCI 的激發能量傳遞主要受整體傳遞路徑的全域組織所支配，並在靜態無序下仍維持高度魯棒性：能量能在各分支內高效率地被傳遞，而通往反應中心的有效捕獲則由該特徵性的動力學橋樑所導引與匯聚。

Photosystem I–light-harvesting complex I (PSI-LHCI) achieves a near-unity quantum yield despite its large size and pronounced structural heterogeneity. While excitation energy transfer (EET) in the PSI core is well characterized, the transfer dynamics of the full PSI-LHCI supercomplex remain unclear. Here, we investigate the dominant EET dynamics of the PSI-LHCI supercomplex from Pisum sativum under static disorder.

A minimum-cut method from graph theory is applied to a representative disorder realization selected at the median of the quantum yield distribution to construct a 14-cluster coarse-grained kinetic model that faithfully reproduces the population dynamics of the full system. The same coarse-graining analysis is further carried out for additional disorder realizations spanning different quantum-yield percentiles, as well as for a disorder-averaged model obtained via consensus clustering over the full ensemble.

In all cases, the resulting coarse-grained descriptions consistently reveal a robust two-branch excitation energy transfer scheme from the peripheral LHCI antenna to the PSI core. This architecture is characterized by fast intra-branch transfer, minimal direct exchange between branches, and a recurrent central bridge cluster that governs access to the reaction center (RC). This consistent two-branch kinetic picture indicates that excitation energy transfer in PSI-LHCI is governed by the global organization of transfer pathways and remains robust under static disorder, with efficient energy transfer occurring within each branch and access to the reaction center funneled through the characteristic kinetic bridge.