Extended protein/water H-bond networks in photosynthetic water oxidation

► Structural basis of proton management in photosynthetic water oxidation. ► A complex polyelectrolyte with evolutionary optimized H-bonding networks (HBN). ► Proton transfer and conformational coupling by protein-internal HBNs. ► Proton management at the lumenal surface by extended Asp/Glu clusters. ► Identification of remarkable proton-storing Asp/Glu dyads.