Dataset Information

Determination of the binding sites of the proton transfer inhibitors Cd2+ and Zn2+ in bacterial reaction centers.

ABSTRACT: The reaction center (RC) from Rhodobacter sphaeroides couples light-driven electron transfer to protonation of a bound quinone acceptor molecule, Q(B), within the RC. The binding of Cd(2+) or Zn(2+) has been previously shown to inhibit the rate of reduction and protonation of Q(B). We report here on the metal binding site, determined by x-ray diffraction at 2.5-A resolution, obtained from RC crystals that were soaked in the presence of the metal. The structures were refined to R factors of 23% and 24% for the Cd(2+) and Zn(2+) complexes, respectively. Both metals bind to the same location, coordinating to Asp-H124, His-H126, and His-H128. The rate of electron transfer from Q(A)(-) to Q(B) was measured in the Cd(2+)-soaked crystal and found to be the same as in solution in the presence of Cd(2+). In addition to the changes in the kinetics, a structural effect of Cd(2+) on Glu-H173 was observed. This residue was well resolved in the x-ray structure-i.e., ordered-with Cd(2+) bound to the RC, in contrast to its disordered state in the absence of Cd(2+), which suggests that the mobility of Glu-H173 plays an important role in the rate of reduction of Q(B). The position of the Cd(2+) and Zn(2+) localizes the proton entry into the RC near Asp-H124, His-H126, and His-H128. Based on the location of the metal, likely pathways of proton transfer from the aqueous surface to Q(B) are proposed.

SUBMITTER: Axelrod HL

PROVIDER: S-EPMC26471 | biostudies-literature | 2000 Feb

REPOSITORIES: biostudies-literature

ACCESS DATA

Publications

Determination of the binding sites of the proton transfer inhibitors Cd2+ and Zn2+ in bacterial reaction centers.

Axelrod H L HL Abresch E C EC Paddock M L ML Okamura M Y MY Feher G G

Proceedings of the National Academy of Sciences of the United States of America 20000201 4

The reaction center (RC) from Rhodobacter sphaeroides couples light-driven electron transfer to protonation of a bound quinone acceptor molecule, Q(B), within the RC. The binding of Cd(2+) or Zn(2+) has been previously shown to inhibit the rate of reduction and protonation of Q(B). We report here on the metal binding site, determined by x-ray diffraction at 2.5-A resolution, obtained from RC crystals that were soaked in the presence of the metal. The structures were refined to R factors of 23% a ...[more]

PMID: 10677497

Similar Datasets

Project description:The role of protein dynamics in the electron transfer from the reduced primary quinone, Q(A)(-), to the secondary quinone, Q(B), was studied at room temperature in isolated reaction centers (RC) from the photosynthetic bacterium Rhodobacter sphaeroides by incorporating the protein in trehalose water systems of different trehalose/water ratios. The effects of dehydration on the reaction kinetics were examined by analyzing charge recombination after different regimes of RC photoexcitation (single laser pulse, double flash, and continuous light) as well as by monitoring flash-induced electrochromic effects in the near infrared spectral region. Independent approaches show that dehydration of RC-containing matrices causes reversible, inhomogeneous inhibition of Q(A)(-)-to-Q(B) electron transfer, involving two subpopulations of RCs. In one of these populations (i.e., active), the electron transfer to Q(B) is slowed but still successfully competing with P(+)Q(A)(-) recombination, even in the driest samples; in the other (i.e., inactive), electron transfer to Q(B) after a laser pulse is hindered, inasmuch as only recombination of the P(+)Q(A)(-) state is observed. Small residual water variations ( approximately 7 wt %) modulate fully the relative fraction of the two populations, with the active one decreasing to zero in the driest samples. Analysis of charge recombination after continuous illumination indicates that, in the inactive subpopulation, the conformational changes that rate-limit electron transfer can be slowed by >4 orders of magnitude. The reported effects are consistent with conformational gating of the reaction and demonstrate that the conformational dynamics controlling electron transfer to Q(B) is strongly enslaved to the structure and dynamics of the surrounding medium. Comparing the effects of dehydration on P(+)Q(A)(-)-->PQ(A) recombination and Q(A)(-)Q(B)-->Q(A)Q(B)(-) electron transfer suggests that conformational changes gating the latter process are distinct from those stabilizing the primary charge-separated state.

Dataset Information

Determination of the binding sites of the proton transfer inhibitors Cd2+ and Zn2+ in bacterial reaction centers.

Publications

Determination of the binding sites of the proton transfer inhibitors Cd2+ and Zn2+ in bacterial reaction centers.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets