title: The plastoquinol-plastoquinone exchange mechanism in photosystem II: insight from molecular dynamics simulations.
abstract: In the photosystem II (PSII) of oxygenic photosynthetic organisms, the reaction center (RC) core mediates the light-induced electron transfer leading to water splitting and production of reduced plastoquinone molecules. The reduction of plastoquinone to plastoquinol lowers PSII affinity for the latter and leads to its release. However, little is known about the role of protein dynamics in this process. Here, molecular dynamics simulations of the complete PSII complex embedded in a lipid bilayer have been used to investigate the plastoquinol release mechanism. A distinct dynamic behavior of PSII in the presence of plastoquinol is observed which, coupled to changes in charge distribution and electrostatic interactions, causes disruption of the interactions seen in the PSII-plastoquinone complex and leads to the "squeezing out" of plastoquinol from the binding pocket. Displacement of plastoquinol closes the second water channel, recently described in a 2.9 Å resolution PSII structure (Guskov et al. in Nat Struct Mol Biol 16:334-342, 2009), allowing to rule out the proposed "alternating" mechanism of plastoquinol-plastoquinone exchange, while giving support to the "single-channel" one. The performed simulations indicated a pivotal role of D1-Ser264 in modulating the dynamics of the plastoquinone binding pocket and plastoquinol-plastoquinone exchange via its interaction with D1-His252 residue. The effects of the disruption of this hydrogen bond network on the PSII redox reactions were experimentally assessed in the D1site-directed mutant Ser264Lys.
authors.affiliation: Theoretical Biology and Bioinformatics Laboratory, Department of Sciences, Roma Tre University, Viale G. Marconi 446, 00146, Rome, Italy.
authors.forename: Veranika
authors.initials: V
authors.lastname: Zobnina
authors.affiliation: Institute of Crystallography CNR, 00015, Monterotondo Scalo, Rome, Italy.
authors.forename: Maya D
authors.initials: MD
authors.lastname: Lambreva
authors.affiliation: Institute of Crystallography CNR, 00015, Monterotondo Scalo, Rome, Italy.
authors.forename: Giuseppina
authors.identifier: http://orcid.org/0000-0001-7353-727X
authors.initials: G
authors.lastname: Rea
authors.affiliation: Institute of Crystallography CNR, 00015, Monterotondo Scalo, Rome, Italy.
authors.forename: Gaetano
authors.initials: G
authors.lastname: Campi
authors.affiliation: Institute of Crystallography CNR, 00015, Monterotondo Scalo, Rome, Italy.
authors.forename: Amina
authors.initials: A
authors.lastname: Antonacci
authors.affiliation: Institute of Crystallography CNR, 00015, Monterotondo Scalo, Rome, Italy.
authors.forename: Viviana
authors.initials: V
authors.lastname: Scognamiglio
authors.affiliation: Institute of Crystallography CNR, 00015, Monterotondo Scalo, Rome, Italy.
authors.forename: Maria Teresa
authors.initials: MT
authors.lastname: Giardi
authors.affiliation: Theoretical Biology and Bioinformatics Laboratory, Department of Sciences, Roma Tre University, Viale G. Marconi 446, 00146, Rome, Italy. fabio.polticelli@uniroma3.it.|National Institute of Nuclear Physics, Roma Tre Section, 00146, Rome, Italy. fabio.polticelli@uniroma3.it.
authors.forename: Fabio
authors.identifier: http://orcid.org/0000-0002-7657-2019
authors.initials: F
authors.lastname: Polticelli
mesh_terms: D006860:Hydrogen Bonding; D008024:Ligands; D056004:Molecular Dynamics Simulation; D045332:Photosystem II Protein Complex / Q000378:metabolism*; D010971:Plastoquinone / Q000031:analogs & derivatives* / Q000378:metabolism*
chemical_list: D008024:Ligands; D045332:Photosystem II Protein Complex; C003165:plastoquinol; D010971:Plastoquinone
keywords: Molecular dynamics simulations; Photosystem II; plastoquinone; Plastoquinol; Plastoquinol release mechanism; Protein dynamics