Electrostatic effects on electron-transfer kinetics in the cytochrome f-plastocyanin complex

Soriano, Glenda M.; Cramer, William A.; Krishtalik, L. I.

doi:10.1016/s0006-3495(97)78351-6

Cited by 43 publications

(49 citation statements)

References 51 publications

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“…Note that small dielectric reorganization in proteins was invoked to explain a variety of kinetic data for charge transfer reactions (1,3,4,(46)(47)(48)(49)(50)(51) and was inferred from molecular simulations (52)(53)(54)(55)(56)(57)(58)(59)(60). Our direct measurements now provide evidence supporting this hypothesis.…”

Section: Discussionsupporting

confidence: 69%

Low dielectric response in enzyme active site

Mertz

Krishtalik

2000

Proc. Natl. Acad. Sci. U.S.A.

125

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The kinetics of charge transfer depend crucially on the dielectric reorganization of the medium. In enzymatic reactions that involve charge transfer, atomic dielectric response of the active site and of its surroundings determines the efficiency of the protein as a catalyst. We report direct spectroscopic measurements of the reorganization energy associated with the dielectric response in the active site of ␣-chymotrypsin. A chromophoric inhibitor of the enzyme is used as a spectroscopic probe. We find that water strongly affects the dielectric reorganization in the active site of the enzyme in solution. The reorganization energy of the protein matrix in the vicinity of the active site is similar to that of low-polarity solvents. Surprisingly, water exhibits an anomalously high dielectric response that cannot be described in terms of the dielectric continuum theory. As a result, sequestering the active site from the aqueous environment inside low-dielectric enzyme body dramatically reduces the dielectric reorganization. This reduction is particularly important for controlling the rate of enzymatic reactions. Many enzymatic reactions are charge transfer processes. Their activation free energy is affected by the dielectric properties of the milieu of the reacting groups (1). It has been suggested that small dielectric response at the active site could be a physical reason for high catalytic activity (2-4).Direct measurements of local dielectric properties at enzyme active sites have never been made. Most of the current knowledge is based on circumstantial evidence. Different existing data can be used to support opposing points of view. For instance, the average static dielectric constant of proteins s Ϸ 4 was estimated from measurements on dry powders (5-9). However, x-ray data indicate that the mobility of atoms near enzymes active sites is higher than average (10, 11) and, thus, the dielectric response should be enhanced. Furthermore, active sites are typically situated within several angstroms of the protein surface. A wide range of dielectric response was predicted from molecular simulations for various proteins: A gradual increase from Ϸ 3 in the center of globule to about Ϸ 10 at its periphery was found in refs. 12-19. Even higher values of 25-35 were calculated by taking into account fluctuations of ionizable surface groups (18,19). Finally, highly polarizable aqueous surroundings may contribute to the dielectric response, to increase the uncertainty even further.Thus, local dielectric properties at enzyme active sites have remained unclear. In the present paper, we attempt to resolve this issue by direct measurement. A spectroscopic technique proposed in refs. 20 and 21 and further developed in refs. 22-24 is used. The reorganization energy is determined from absorption and emission spectra of proflavine noncovalently bound in the active site of ␣-chymotrypsin. We evaluate the contributions to the dielectric reorganization of the protein interior and of the surrounding solvent by comparing the spectra of t...

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Section: Discussionsupporting

confidence: 69%

Low dielectric response in enzyme active site

Mertz

Krishtalik

2000

Proc. Natl. Acad. Sci. U.S.A.

125

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“…In Phormidium, Pc binds Cf in a "head-on" conformation in which the hydrophobic patch accounts for the whole recognition interface in Pc, contrary to the "side-on" interface that also involves the acidic patches, which is found in the plant complex. Both kinds of complexes have been predicted in theoretical studies using the co-ordinates from plant proteins (15)(16)(17). The ionic strength dependences of the structures suggest that in the plant complex electrostatics play a dominant role, whereas in Phormidium complex formation is governed by the hydrophobic effect.…”

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confidence: 99%

Structure of the Complex between Plastocyanin and Cytochrome f from the Cyanobacterium Nostoc sp. PCC 7119 as Determined by Paramagnetic NMR

Dı́az-Moreno

Díaz-Quintana

Rosa

et al. 2005

Journal of Biological Chemistry

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The complex between cytochrome f and plastocyanin from the cyanobacterium Nostoc has been characterized by NMR spectroscopy. The binding constant is 16 mM ؊1 , and the lifetime of the complex is much less than 10 ms. Intermolecular pseudo-contact shifts observed for the plastocyanin amide nuclei, caused by the heme iron, as well as the chemical-shift perturbation data were used as the sole experimental restraints to determine the orientation of plastocyanin relative to cytochrome f with a precision of 1.3 Å. The data show that the hydrophobic patch surrounding tyrosine 1 in cytochrome f docks the hydrophobic patch of plastocyanin. Charge complementarities are found between the rims of the respective recognition sites of cytochrome f and plastocyanin. Significant differences in the relative orientation of both proteins are found between this complex and those previously reported for plants and Phormidium, indicating that electrostatic and hydrophobic interactions are balanced differently in these complexes.

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“…Several different computational approaches to elucidate the structure of the bimolecular complex formed between spinach or poplar Pc and turnip Cyt f have been employed. Manual docking was first attempted us-ing information derived by mapping the electrostatic field on the proteins surface (17,18). Subsequently, molecular dynamics (19) and Brownian dynamics (20,21) were employed.…”

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confidence: 99%