title: Probing the accessibility of the Mn(4)Ca cluster in photosystem II: channels calculation, noble gas derivatization, and cocrystallization with DMSO.
abstract: Using the 2.9 A resolution structure of the membrane-intrinsic protein-cofactor complex photosystem II (PSII) from the cyanobacterium Thermosynechococcus elongatus, we calculated and characterized nine possible substrate/product channels leading to/away from the Mn(4)Ca cluster, where water is oxidized to dioxygen, protons, and electrons. Five narrow channels could function in proton transport, assuming that no large structural changes are associated with water oxidation. Four wider channels could serve to supply water to or remove oxygen from the Mn(4)Ca cluster. One of them might be regulated by conformational changes of Lys134 in subunit PsbU. Data analyses of Kr derivatized crystals and complexes with dimethyl sulfoxide (DMSO) confirm the accessibility of the proposed dioxygen channels to other molecules. Results from Xe derivatization suggest that the lipid clusters within PSII could serve as a drain for oxygen because of their predominant hydrophobic character and mediate dioxygen release from the lumen.
authors.affiliation: Institut für Chemie und Biochemie/Kristallographie, Freie Universität Berlin, Berlin, Germany.
authors.forename: Azat
authors.initials: A
authors.lastname: Gabdulkhakov
authors.forename: Albert
authors.initials: A
authors.lastname: Guskov
authors.forename: Matthias
authors.initials: M
authors.lastname: Broser
authors.forename: Jan
authors.initials: J
authors.lastname: Kern
authors.forename: Frank
authors.initials: F
authors.lastname: Müh
authors.forename: Wolfram
authors.initials: W
authors.lastname: Saenger
authors.forename: Athina
authors.initials: A
authors.lastname: Zouni
mesh_terms: D003460:Crystallization; D004121:Dimethyl Sulfoxide / Q000737:chemistry*; D008345:Manganese / Q000737:chemistry*; D008958:Models, Molecular; D015335:Molecular Probes; D005741:Noble Gases / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry; D045332:Photosystem II Protein Complex / Q000737:chemistry*
chemical_list: D015335:Molecular Probes; D005741:Noble Gases; D045332:Photosystem II Protein Complex; D008345:Manganese; D010100:Oxygen; D004121:Dimethyl Sulfoxide