Proton transfer pathway from the oxygen-evolving complex in photosystem II substantiated by extensive mutagenesis

We report a structure-based biological approach to identify the proton-transfer pathway in photosystem II. First, molecular dynamics (MD) simulations were conducted analyze H-bond network that may serve as Grotthuss-like proton conduit. MD show D1-Asp61, acceptor of H2O at Mn4CaO5 cluster (W1), forms an via one water molecule with D1-Glu65 but not D2-Glu312. Then, D1-Glu65, D2-Glu312, and adjacent residues, D1-Arg334, D2-Glu302, D2-Glu323, thoroughly mutated other 19 i.e., 114 Chlamydomonas chloroplast mutant cells generated. Mutation D1-Asp61 was most crucial. Only D61E D61C grew photoautotrophically exhibit O2-evolving activity. Mutations D2-Glu312 less crucial photosynthetic growth than mutations D1-Glu65. Quantum mechanical/molecular mechanical calculations indicated PSII crystal structure, is predominantly localized along pKa(D1-Glu65) > pKa(D2-Glu312). The potential-energy profile shows release from leads formation two short H-bonds between which facilitates downhill transfer conduit S2 S3 transition. It seems possible involved dominant proceeds W1 toward thylakoid lumen, whereas D1-Arg334 be alternative pathways some mutants.