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Dive into the research topics where Eric L. Klein is active.

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Featured researches published by Eric L. Klein.


Journal of Magnetic Resonance | 2011

Pulsed dipolar spectroscopy distance measurements in biomacromolecules labeled with Gd(III) markers

Ying Song; Thomas J. Meade; Andrei V. Astashkin; Eric L. Klein; John H. Enemark; Arnold M. Raitsimring

This work demonstrates the feasibility of using Gd(III) tags for long-range Double Electron Electron Resonance (DEER) distance measurements in biomacromolecules. Double-stranded 14- base pair Gd(III)-DNA conjugates were synthesized and investigated at K(a) band. For the longest Gd(III) tag the average distance and average deviation between Gd(III) ions determined from the DEER time domains was about 59±12Å. This result demonstrates that DEER measurements with Gd(III) tags can be routinely carried out for distances of at least 60Å, and analysis indicates that distance measurements up to 100Å are possible. Compared with commonly used nitroxide labels, Gd(III)-based labels will be most beneficial for the detection of distance variations in large biomacromolecules, with an emphasis on large scale changes in shape or distance. Tracking the folding/unfolding and domain interactions of proteins and the conformational changes in DNA are examples of such applications.


Inorganic Chemistry | 2009

Direct Detection and Characterization of Chloride in the Active Site of the Low-pH Form of Sulfite Oxidase Using Electron Spin Echo Envelope Modulation Spectroscopy, Isotopic Labeling, and Density Functional Theory Calculations

Eric L. Klein; Andrei V. Astashkin; Dmitry Ganyushin; Christoph Riplinger; Kayunta Johnson-Winters; Frank Neese; John H. Enemark

Electron spin echo envelope modulation (ESEEM) investigations were carried out on samples of the low-pH (lpH) form of vertebrate sulfite oxidase (SO) prepared with (35)Cl- and (37)Cl-enriched buffers, as well as with buffer containing the natural abundance of Cl isotopes. The isotope-related changes observed in the ESEEM spectra provide direct and unequivocal evidence that Cl(-) is located in close proximity to the Mo(V) center of lpH SO. The measured isotropic hyperfine interaction constant of about 4 MHz ((35)Cl) suggests that the Cl(-) ion is either weakly coordinated to Mo(V) at its otherwise vacant axial position, trans to the oxo ligand, or is hydrogen-bonded to the equatorial exchangeable OH ligand. Scalar relativistic all-electron density functional theory (DFT) calculations of the hyperfine and nuclear quadrupole interaction parameters, along with steric and energetic arguments, strongly support the possibility that Cl(-) is hydrogen-bonded to the equatorial OH ligand rather than being directly coordinated to the Mo(V).


Physical Chemistry Chemical Physics | 2009

Exchangeable oxygens in the vicinity of the molybdenum center of the high-pH form of sulfite oxidase and sulfite dehydrogenase

Andrei V. Astashkin; Eric L. Klein; Dmitry Ganyushin; Kayunta Johnson-Winters; Frank Neese; Ulrike Kappler; John H. Enemark

The electron spin echo envelope modulation (ESEEM) investigation of the high-pH (hpH) form of sulfite oxidase (SO) and sulfite dehydrogenase (SDH) prepared in buffer enriched with H(2)(17)O reveals the presence of three types of exchangeable oxygen atoms at the molybdenum center. Two of these oxygen atoms belong to the equatorial OH ligand and the axial oxo ligand, and are characterized by (17)O hyperfine interaction (hfi) constants of about 37 MHz and 6 MHz, respectively. The third oxygen has an isotropic hfi constant of 3-4 MHz and likely belongs to a hydroxyl moiety hydrogen-bonded to the equatorial OH ligand. This exchangeable oxygen atom is not observed in the ESEEM spectra of the Y236F mutant of SDH, where the active site tyrosine has been replaced by phenylalanine.


Biochemistry | 2011

Structural studies of the molybdenum center of mitochondrial amidoxime reducing component (mARC) by pulsed EPR spectroscopy and 17O-labeling.

Asha Rajapakshe; Andrei V. Astashkin; Eric L. Klein; Debora Reichmann; Ralf R. Mendel; Florian Bittner; John H. Enemark

Mitochondrial amidoxime reducing components (mARC-1 and mARC-2) represent a novel group of Mo-containing enzymes in eukaryotes. These proteins form the catalytic part of a three-component enzyme complex known to be responsible for the reductive activation of several N-hydroxylated prodrugs. No X-ray crystal structures are available for these enzymes as yet. A previous biochemical investigation [Wahl, B., et al. (2010) J. Biol. Chem., 285, 37847-37859 ] has revealed that two of the Mo coordination positions are occupied by sulfur atoms from a pyranopterindithiolate (molybdopterin, MPT) cofactor. In this work, we have used continuous wave and pulsed electron paramagnetic resonance (EPR) spectroscopy and density functional theoretical (DFT) calculations to determine the nature of remaining ligands in the Mo(V) state of the active site of mARC-2. Experiments with samples in D(2)O have identified the exchangeable equatorial ligand as a hydroxyl group. Experiments on samples in H(2)(17)O-enriched buffer have shown the presence of a slowly exchangeable axial oxo ligand. Comparison of the experimental (1)H and (17)O hyperfine interactions with those calculated using DFT has shown that the remaining nonexchangeable equatorial ligand is, most likely, protein-derived and that the possibility of an equatorial oxo ligand can be excluded.


Journal of the American Chemical Society | 2008

Structural Studies of the Molybdenum Center of the Pathogenic R160Q Mutant of Human Sulfite Oxidase by Pulsed EPR Spectroscopy and 17O and 33S Labeling

Andrei V. Astashkin; Kayunta Johnson-Winters; Eric L. Klein; Changjian Feng; Heather L. Wilson; K. V. Rajagopalan; Arnold M. Raitsimring; John H. Enemark


Inorganic Chemistry | 2012

Identity of the Exchangeable Sulfur-Containing Ligand at the Mo(V) Center of R160Q Human Sulfite Oxidase

Eric L. Klein; Arnold M. Raitsimring; Andrei V. Astashkin; Asha Rajapakshe; Kayunta Johnson-Winters; Anna R. Arnold; Alexei Potapov; Daniella Goldfarb; John H. Enemark


Journal of the American Chemical Society | 2007

Direct Demonstration of the Presence of Coordinated Sulfate in the Reaction Pathway of Arabidopsis thaliana Sulfite Oxidase Using 33S Labeling and ESEEM Spectroscopy

Andrei V. Astashkin; Kayunta Johnson-Winters; Eric L. Klein; Robert S. Byrne; Russ Hille; and Arnold M. Raitsimring; John H. Enemark


Coordination Chemistry Reviews | 2013

Applications of pulsed EPR spectroscopy to structural studies of sulfite oxidizing enzymes

Eric L. Klein; Andrei V. Astashkin; Arnold M. Raitsimring; John H. Enemark


Journal of Inorganic Biochemistry | 2007

Toward modeling the high chloride, low pH form of sulfite oxidase: Ka-band ESEEM of equatorial chloro ligands in oxomolybdenum(V) complexes

Andrei V. Astashkin; Eric L. Klein; John H. Enemark


Inorganic Chemistry | 2011

Metal–Sulfur Valence Orbital Interaction Energies in Metal–Dithiolene Complexes: Determination of Charge and Overlap Interaction Energies by Comparison of Core and Valence Ionization Energy Shifts

Nicholas J. Wiebelhaus; Matthew A. Cranswick; Eric L. Klein; L. Tori Lockett; Dennis L. Lichtenberger; John H. Enemark

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