The iron stress-induced protein A (IsiA) is a source of interest and debate in biological research. The IsiA supercomplex, binding over 200 chlorophylls, assembles in multimeric rings around photosystem I (PSI). Recently, the IsiA–PSI structure from Synechocystis sp. PCC 6803 was resolved to 3.48 Å. Based on this structure, we created a model simulating a single excitation event in an IsiA monomer. This model enabled us to calculate the fluorescence and the localization of the excitation in the IsiA structure. To further examine this system, noise was introduced to the model in two forms—thermal and positional. Introducing noise highlights the functional differences in the system between cryogenic temperatures and biologically relevant temperatures. Our results show that the energetics of the IsiA pigment–protein complex are very robust at room temperature. Nevertheless, shifts in the position of specific chlorophylls lead to large changes in their optical and fluorescence properties. Based on these results, we discuss the implication of highly robust structures, with potential for serving different roles in a context-dependent manner, on our understanding of the function and evolution of photosynthetic processes.

中文翻译：

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基于结构的 IsiA 哈密顿模型揭示了高度稳健的色素-蛋白质复合物

铁应激诱导蛋白 A (IsiA) 是生物学研究中引起兴趣和争论的一个来源。IsiA 超级复合物结合了 200 多种叶绿素，在光系统 I (PSI) 周围组装成多聚体环。最近，来自集胞藻属的 IsiA-PSI 结构。PCC 6803 的分辨率为 3.48 Å。基于这种结构，我们创建了一个模型来模拟 IsiA 单体中的单个激发事件。该模型使我们能够计算 IsiA 结构中的荧光和激发的定位。为了进一步检查该系统，以两种形式将噪声引入模型：热噪声和位置噪声。噪声的引入凸显了系统中低温和生物相关温度之间的功能差异。我们的结果表明，IsiA 色素-蛋白质复合物的能量学在室温下非常稳定。然而，特定叶绿素位置的变化会导致其光学和荧光特性发生巨大变化。基于这些结果，我们讨论了高度稳健的结构对我们理解光合作用过程的功能和进化的影响，该结构具有以上下文相关的方式发挥不同作用的潜力。