Design Principals of Photobiological Metabolism

细胞新陈代谢包括生物体获取、储存和释放对不断变化的需求和环境条件做出反应所需的因子的基本过程。在光合作用的生物体中，细胞新陈代谢的基础来自于对太阳能的可控捕获和利用，这一过程对几乎所有陆地生命都是必不可少的。从化学上讲，光合作用的早期反应包括吸收入射太阳光并将其转化为低势电子，这些电子可用于驱动各种新陈代谢过程，包括碳固定。电子流向不同代谢过程的调节在很大程度上是通过电子载体铁氧还蛋白的作用来控制的。然而，铁氧还蛋白优先将低势电子捐献给一条代谢途径而不是另一条代谢途径的机制尚不清楚。为此，我建议研究长聚球藻PCC7942中铁氧还蛋白产生的电子通量的可塑性。具体地说，我提出了一系列实验，旨在将低势电子重新定向到细胞氢酶，细胞氢酶催化氢气的产生，作为可接受的电子的读数。拟议的实验涉及构建蓝细菌菌株，该菌株具有竞争低势电子的代谢途径的可诱导下调，以及具有铁氧还蛋白和氢酶的菌株的空间限制，这些菌株通过表达嵌合蛋白或合成蛋白支架而被限制在一起。这些实验将导致构建能够直接从阳光中产生氢气的蓝藻菌株。这些实验结果将对理解光合作用代谢具有重要意义。此外，这些实验将对光合作用驱动的生产生物医学化合物和可持续、清洁生物燃料的途径的工程具有广泛的影响。

Cellular metabolism encompasses the fundamental processes by which organisms acquire, store, and release factors required to respond to changing needs and environmental conditions. In photosynthesizing organisms, the basis for cellular metabolism is drawn from the controlled capture and utilization of solar energy, a process which is essential for virtually all terrestrial life. Chemically, the early reactions of photosynthesis involve the absorption of incident solar light and its conversion into low potential electrons that can be used to drive a variety of metabolic processes, including carbon fixation. Regulation of the direction of electron flux towards different metabolic processes is largely controlled through the actions of the electron carrier, ferredoxin. However, the mechanism by which ferredoxin preferentially donates low potential electrons to one metabolic pathway over another is poorly understood. To this end, I propose to examine the plasticity of electron flux from ferredoxin within the cyanobacterium Synechococcus elongatus PCC7942. Specifically, I propose a series of experiments designed to redirect low potential electrons towards cellular hydrogenases, which catalyze the production of hydrogen gas as a readout of accepted electrons. Proposed experiments involve the construction of cyanobacterial strains with inducible downregulation of metabolic pathways competing for low potential electrons as well as strains with ferredoxin and hydrogenases spatially constrained together by expression of chimeric proteins or synthetic protein scaffolds. These experiments will result in the construction of strains of cyanobacteria capable of producing hydrogen gas directly from sunlight. The results of these experiments will have relevance for the understanding of photosynthetic metabolism. Furthermore, these experiments will have broad implications for the engineering of photosynthesis-driven pathways for the production of biomedical compounds and sustainable, clean biofuels.