Nonplanar porphyrins and their significance in proteins

Shelnutt, John A.; Song, Xing-Zhi; Ma, Jie; Jia, Song‐Ling; Jentzen, Walter; Medforth, Craig J.

doi:10.1039/a827031z

Cited by 822 publications

(958 citation statements)

References 35 publications

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“…It is well known from metalloporphin macrocycles to conserve its shape during evolution if it is of functional relevance (36). It appears that such functional conservation principle has to be extended to functional cofactor-matrix units.…”

Section: N Photo-cidnp Mas Nmr On Ps2mentioning

confidence: 99%

¹⁵ N photochemically induced dynamic nuclear polarization magic-angle spinning NMR analysis of the electron donor of photosystem II

Diller

Roy

Gast

et al. 2007

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

110

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In natural photosynthesis, the two photosystems that operate in series to drive electron transport from water to carbon dioxide are quite similar in structure and function, but operate at widely different potentials. In both systems photochemistry begins by photo-oxidation of a chlorophyll a, but that in photosystem II (PS2) has a 0.7 eV higher midpoint potential than that in photosystem I (PS1), so their electronic structures must be very different. Using reaction centers from 15 N-labeled spinach, these electronic structures are compared by their photochemically induced dynamic nuclear polarization (photo-CIDNP) in magic-angle spinning (MAS) NMR measurements. The results show that the electron spin distribution in PS1, apart from its known delocalization over 2 chlorophyll molecules, reveals no marked disturbance, whereas the pattern of electron spin density distribution in PS2 is inverted in the oxidized radical state. A model for the donor of PS2 is presented explaining the inversion of electron spin density based on a tilt of the axial histidine toward pyrrole ring IV causing -overlap of both aromatic systems.photosynthesis ͉ photosystem I ͉ solid-state NMR ͉ electron transfer ͉ redox potential I n photosynthesis, the two photosystems that operate in series to drive electron transport from water to carbon dioxide are similar in structure and function, but operate at widely different potentials. In both photosystems, photochemistry begins by photo-oxidation of a chlorophyll a (Chl). The oxidized electron donor of photosystem II (PS2) is the strongest oxidizing agent known in living nature, having a redox potential of ϩ 1.2V (1), required for water oxidation. The electronically excited donor of photosystem I (PS1), probably the most reducing compound in living nature (2), initiates the dark reaction. The question arises what factors tune those electronic properties. The spatial structure of PS2 (Fig. 1) shows two inner Chls (P D1 and P D2 ), two accessory Chls (Chl D1 and Chl D2 ), two pheophytin a (Phe) cofactors and two quinones in an arrangement similar to that in bacterial reaction centers (RCs) of purple bacteria.Photochemically induced dynamic nuclear polarization (photo-CIDNP) magic-angle spinning (MAS) NMR is an optical solidstate NMR method using the high electron polarization in the correlated electron pair and allows for strong increase of sensitivity and selectivity (4, 5) allowing to study the electronic structure of photosynthetic cofactors in great detail. The solid-state photo-CIDNP effect, discovered in 1994 (6), relies on different mechanisms called three-spin mixing (7), differential decay (8), and differential relaxation (9, 10). Recently, the contribution of these three mechanisms has been analyzed by field-dependent measurements on unlabeled RCs of the purple bacterium Rhodobacter sphaeroides (11,12). The chemical shift refers to the electronic ground-state after the photocycle, the photo-CIDNP signal intensity is linked to the intermediate radical state. Analytical expressions imply tha...

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Section: N Photo-cidnp Mas Nmr On Ps2mentioning

confidence: 99%

¹⁵ N photochemically induced dynamic nuclear polarization magic-angle spinning NMR analysis of the electron donor of photosystem II

Diller

Roy

Gast

et al. 2007

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

110

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“…The use of mass-weighted coordinates is essential for modes involving significant Fe motion and distinguishes the correlation matrix in Eq. (10) from related approaches 46 that neglect mass variations. The method presented here mirrors the vibrational projection analysis introduced by Grafton and Wheeler, who have elucidated the advantages of this approach.…”

Section: A Mode Correlation Analysismentioning

confidence: 99%

“…41,42 However, these measurements do not exclude other vibrations that may appear in this frequency range, such as the FeCO distortion mode (in-phase bend/tilt) in iron carbonyl porphyrins [43][44][45] or other heme distortions that may control redox reactions. 46,47 The weak sensitivity of low frequencies to isotopic substitution presents a significant obstacle to associating specific atomic motions with observed frequencies. In contrast, NRVS measurements on oriented single crystals definitively identify Fe motion orthogonal to the heme plane associated with low frequency modes in model compounds.…”

Section: Introductionmentioning

confidence: 99%

Spectroscopic identification of reactive porphyrin motions

Barabanschikov

Demidov

Kubo

et al. 2011

The Journal of Chemical Physics

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Nuclear resonance vibrational spectroscopy (NRVS) reveals the vibrational dynamics of a Mössbauer probe nucleus. Here, 57 Fe NRVS measurements yield the complete spectrum of Fe vibrations in halide complexes of iron porphyrins. Iron porphine serves as a useful symmetric model for the more complex spectrum of asymmetric heme molecules that contribute to numerous essential biological processes. Quantitative comparison with the vibrational density of states (VDOS) predicted for the Fe atom by density functional theory calculations unambiguously identifies the correct sextet ground state in each case. These experimentally authenticated calculations then provide detailed normal mode descriptions for each observed vibration. All Fe-ligand vibrations are clearly identified despite the high symmetry of the Fe environment. Low frequency molecular distortions and acoustic lattice modes also contribute to the experimental signal. Correlation matrices compare vibrations between different molecules and yield a detailed picture of how heme vibrations evolve in response to (a) halide binding and (b) asymmetric placement of porphyrin side chains. The side chains strongly influence the energetics of heme doming motions that control Fe reactivity, which are easily observed in the experimental signal.

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“…It is the protein environment surrounding the heme that determines the extent of prosthetic group distortion that is conserved among members of a given superfamily (26). Quantitation of deviation from planarity of the heme by the method developed by Shellnut et al (27) gives a value for the total out-of-plane distortion for the AOS heme of 0.11 Å, a number within the coordinate error for the structure determination. In contrast, the same value for HEC, a structure determined to 1.5-Å resolution, is 0.72 Å.…”

Section: The Chemical Nature Of the U-shaped Cavity Is Complementarymentioning

confidence: 99%

The structure of coral allene oxide synthase reveals a catalase adapted for metabolism of a fatty acid hydroperoxide

Oldham

Brash

Newcomer

2004

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

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8R-Lipoxygenase and allene oxide synthase (AOS) are parts of a naturally occurring fusion protein from the coral Plexaura homomalla. AOS catalyses the production of an unstable epoxide (an allene oxide) from the fatty acid hydroperoxide generated by the lipoxygenase activity. Here, we report the structure of the AOS domain and its striking structural homology to catalase. Whereas nominal sequence identity between the enzymes had been previously described, the extent of structural homology observed was not anticipated, given that this enzyme activity had been exclusively associated with the P450 superfamily, and conservation of a catalase fold without catalase activity is unprecedented. Whereas the heme environment is largely conserved, the AOS heme is planar and the distal histidine is flanked by two hydrogen-bonding residues. These critical differences likely facilitate the switch from a catalatic activity to that of a fatty acid hydroperoxidase.eicosanoids ͉ heme

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Nonplanar porphyrins and their significance in proteins

Cited by 822 publications

References 35 publications

¹⁵ N photochemically induced dynamic nuclear polarization magic-angle spinning NMR analysis of the electron donor of photosystem II

¹⁵ N photochemically induced dynamic nuclear polarization magic-angle spinning NMR analysis of the electron donor of photosystem II

Spectroscopic identification of reactive porphyrin motions

The structure of coral allene oxide synthase reveals a catalase adapted for metabolism of a fatty acid hydroperoxide

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Nonplanar porphyrins and their significance in proteins

Cited by 822 publications

References 35 publications

15 N photochemically induced dynamic nuclear polarization magic-angle spinning NMR analysis of the electron donor of photosystem II

15 N photochemically induced dynamic nuclear polarization magic-angle spinning NMR analysis of the electron donor of photosystem II

Spectroscopic identification of reactive porphyrin motions

The structure of coral allene oxide synthase reveals a catalase adapted for metabolism of a fatty acid hydroperoxide

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¹⁵ N photochemically induced dynamic nuclear polarization magic-angle spinning NMR analysis of the electron donor of photosystem II

¹⁵ N photochemically induced dynamic nuclear polarization magic-angle spinning NMR analysis of the electron donor of photosystem II