Structural and Functional Dynamics of Microbial Photosystem Complexes

Photosynthesis involves two stages, the light reactions and the dark reactions that occur in thylakoid membranes and stroma, respectively. The primary function of the light reactions is to generate biochemical reductant (NADPH2) and chemical energy (ATP) which are essential for the assimilation of inorganic carbon. Phototrophy is powered by Photosystem I and Photosystem II reaction centers which are classified by their absorption spectra, the order of electron transfer reactions, and terminal electron acceptors. Photosystem II plays a key role in the oxidation of water to molecular oxygen and the generation of ATP through photophosphorylation. PSII is a multimeric complex located in the thylakoid membrane, with three main components: the reaction center, the oxygen-evolving complex, and the inner light-harvesting antennae. The PSII reaction center contains D1 and D2 proteins and is responsible for the charge separation and stabilization. The PSI consists of P700, A0, A1, and iron-sulfur clusters FX, FA, and FB, which ultimately transfer electrons to ferredoxin (Fd) and ferredoxin-NADP+ reductase (FNR). The extrinsic and low molecular weight proteins in photosystem complexes work together to optimize the transfer of energy and electrons, stabilize the complex, and protect it from damage. Additionally, mutations or alterations in these proteins can lead to reduced photosynthetic efficiency and negatively impact growth and survival. Understanding the function and interactions of these proteins is important for improving yields and developing more efficient photosynthetic cell factories for various industrial applications.