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

• Published in: Biochimica et biophysica acta. Bioenergetics Vol. 1862; no. 1; p. 148329
• Main Authors: Kuroda, Hiroshi, Kawashima, Keisuke, Ueda, Kazuyo, Ikeda, Takuya, Saito, Keisuke, Ninomiya, Ryo, Hida, Chisato, Takahashi, Yuichiro, Ishikita, Hiroshi
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.01.2021
• Subjects: Chlamydomonas - enzymology; Chlamydomonas - genetics; Models, Chemical; Models, Molecular; Molecular dynamics simulations; Oxygen - chemistry; Oxygen - metabolism; Oxygen-evolving activity; Photosystem II; Photosystem II Protein Complex - chemistry; Photosystem II Protein Complex - genetics; Photosystem II Protein Complex - metabolism; Proton transfer pathway; Protons; Quantum mechanical/molecular mechanical calculations; Oxygen-evolving activity; Photosystem II; Proton transfer pathway; Molecular dynamics simulations; Quantum mechanical/molecular mechanical calculations
• ISSN: 0005-2728; 1879-2650
• DOI: 10.1016/j.bbabio.2020.148329

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