title: Putative hydrogen bond to tyrosine M208 in photosynthetic reaction centers from Rhodobacter capsulatus significantly slows primary charge separation.
abstract: Slow, ∼50 ps, P* → P(+)HA(-) electron transfer is observed in Rhodobacter capsulatus reaction centers (RCs) bearing the native Tyr residue at M208 and the single amino acid change of isoleucine at M204 to glutamic acid. The P* decay kinetics are unusually homogeneous (single exponential) at room temperature. Comparative solid-state NMR of [4'-(13)C]Tyr labeled wild-type and M204E RCs show that the chemical shift of Tyr M208 is significantly altered in the M204E mutant and in a manner consistent with formation of a hydrogen bond to the Tyr M208 hydroxyl group. Models based on RC crystal structure coordinates indicate that if such a hydrogen bond is formed between the Glu at M204 and the M208 Tyr hydroxyl group, the -OH would be oriented in a fashion expected (based on the calculations by Alden et al., J. Phys. Chem. 1996, 100, 16761-16770) to destabilize P(+)BA(-) in free energy. Alteration of the environment of Tyr M208 and BA by Glu M204 via this putative hydrogen bond has a powerful influence on primary charge separation.
authors.affiliation: Department of Chemistry, Stanford University , Stanford, California 94305-5012, United States.
authors.forename: Miguel
authors.initials: M
authors.lastname: Saggu
authors.forename: Brett
authors.initials: B
authors.lastname: Carter
authors.forename: Xiaoxue
authors.initials: X
authors.lastname: Zhou
authors.forename: Kaitlyn
authors.initials: K
authors.lastname: Faries
authors.forename: Lynette
authors.initials: L
authors.lastname: Cegelski
authors.forename: Dewey
authors.initials: D
authors.lastname: Holten
authors.forename: Steven G
authors.initials: SG
authors.lastname: Boxer
authors.forename: Christine
authors.initials: C
authors.lastname: Kirmaier
mesh_terms: D019943:Amino Acid Substitution; D002247:Carbon Isotopes / Q000737:chemistry; D006860:Hydrogen Bonding; D007700:Kinetics; D019906:Nuclear Magnetic Resonance, Biomolecular; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000378:metabolism; D016354:Rhodobacter capsulatus / Q000378:metabolism*; D013696:Temperature; D014443:Tyrosine / Q000737:chemistry*
chemical_list: D002247:Carbon Isotopes; D045322:Photosynthetic Reaction Center Complex Proteins; D014443:Tyrosine