Michelle Dicus - Academia.edu (original) (raw)
Papers by Michelle Dicus
![Research paper thumbnail of Multifrequency Pulsed EPR investigation of Fehistidine Interaction of the Uniquely Coordinated [2Fe2S] Cluster in the Outer Mitochondrial Membrane Protein, MitoNEET](https://attachments.academia-assets.com/39950310/thumbnails/1.jpg)
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Biochemistry, 2009
The Rieske protein from Thermus thermophilus (TtRp) and a truncated version of the protein (trunc... more The Rieske protein from Thermus thermophilus (TtRp) and a truncated version of the protein (truncTtRp), produced to achieve a low-pH crystallization condition, have been characterized using UV-visible and circular dichroism spectroscopies. TtRp and truncTtRp undergo a change in the UV-visible spectra with increasing pH. The LMCT band at 458 nm shifts to 436 nm and increases in intensity. The increase at 436 nm versus pH can be fit using the sum of two Henderson-Hasselbalch equations, yielding two pK(a) values for the oxidized protein. For TtRp, pK(ox1) = 7.48 +/- 0.12 and pK(ox2) = 10.07 +/- 0.17. For truncTtRp, pK(ox1) = 7.87 +/- 0.17 and pK(ox2) = 9.84 +/- 0.42. The shift to shorter wavelength and the increase in intensity for the LMCT band with increasing pH are consistent with deprotonation of the histidine ligands. A pH titration of truncTtRp monitored by circular dichroism also showed pH-dependent changes at 315 and 340 nm. At 340 nm, the fit gives pK(ox1) = 7.14 +/- 0.26 and pK(ox2) = 9.32 +/- 0.36. The change at 315 nm is best fit for a single deprotonation event, giving pK(ox1) = 7.82 +/- 0.10. The lower wavelength region of the CD spectra was unaffected by pH, indicating that the overall fold of the protein remains unchanged, which is consistent with crystallographic results of truncTtRp. The structure of truncTtRp crystallized at pH 6.2 is very similar to TtRp at pH 8.5 and contains only subtle changes localized at the [2Fe-2S] cluster. These titration and structural results further elucidate the histidine ligand characteristics and are consistent with important roles for these amino acids.
Biochimica et Biophysica Acta (BBA) - Bioenergetics, 2004
The pulsed electron paramagnetic resonance (EPR) methods of electron spin echo envelope modulatio... more The pulsed electron paramagnetic resonance (EPR) methods of electron spin echo envelope modulation (ESEEM) and electron spin echoelectron nuclear double resonance (ESE-ENDOR) are used to investigate the structure of the Photosystem II oxygen-evolving complex (OEC), including the paramagnetic manganese cluster and its immediate surroundings. Recent unpublished results from the pulsed EPR laboratory at UC-Davis are discussed, along with aspects of recent publications, with a focus on substrate and cofactor interactions. New data on the proximity of exchangeable deuterons around the Mn cluster poised in the S 0 -state are presented and interpreted. These pulsed EPR results are used in an evaluation of several recently proposed mechanisms for PSII water oxidation. We strongly favor mechanistic models where the substrate waters bind within the OEC early in the S-state cycle. Models in which the OUO bond is formed by a nucleophilic attack by a Ca 2 + -bound water on a strong S 4 -state electrophile provide a good match to the pulsed EPR data. D
Applied Magnetic Resonance, 2007
Electron paramagnetic resonance studies at multiple frequencies (MF EPR) can provide detailed ele... more Electron paramagnetic resonance studies at multiple frequencies (MF EPR) can provide detailed electronic structure descriptions of unpaired electrons in organic radicals, inorganic complexes, and metalloenzymes. Analysis of these properties aids in the assignment of the chemical environment surrounding the paramagnet and provides mechanistic insight into the chemical reactions in which these systems take part. Herein, we present results from pulsed EPR studies performed at three different frequencies (9, 31, and 130 GHz) on [Mn(II)(H 2 O) 6 ] 2! , Mn(II) adducts with the nucleotides ATP and GMP, and the Mn(II)-bound form of the hammerhead ribozyme (MnHH). Through line shape analysis and interpretation of the zero-field splitting values derived from successful simulations of the corresponding continuous-wave and field-swept echo-detected spectra, these data are used to exemplify the ability of the MF EPR approach in distinguishing the nature of the first ligand sphere. A survey of recent results from pulsed EPR, as well as pulsed electronnuclear double resonance and electron spin echo envelope modulation spectroscopic studies applied to Mn(II)-dependent systems, is also presented.
Analytical Chemistry, 1983
![Research paper thumbnail of Binding of Histidine in the (Cys) 3 (His) 1 -Coordinated [2Fe−2S] Cluster of Human mitoNEET](https://attachments.academia-assets.com/39842612/thumbnails/1.jpg)
](Journal of the American Chemical Society, 2010
Human mitoNEET is a homodimeric iron-sulfur protein located in the outer mitochondrial membrane w... more Human mitoNEET is a homodimeric iron-sulfur protein located in the outer mitochondrial membrane with unknown function, but which is known to interact with thiazolidinedione diabetes drugs. Each monomer houses a [2Fe-2S] cluster with an unusual (Cys) 3 (His) 1 ligation. The His ligand is important for enabling cluster release and for tuning the redox potential. We use multi-frequency (X-, Ka-, Qband) and multi-technique (CW, ESEEM, ENDOR, HYSCORE) EPR spectroscopy to investigate the cluster in its paramagnetic reduced [Fe 2+ Fe 3+ ] (S = 1/2) state. It has a rhombic g-tensor (2.007, 1.937, 1.897) with an average g-value of 1.947 that falls between those of Rieske-type and ferredoxintype [2Fe-2S] clusters. Simulation and least-squares fitting of orientation-selective Ka-and Q-band ENDOR, 1D ESEEM and HYSCORE spectra of 14 N and 15 N-labelled mitoNEET yield the principal values and orientations of both the hyperfine tensor ( 14 N: A iso = −6.25 MHz, T = −0.94 MHz) and the quadrupolar tensor (e 2 Qq/h = −2.47 MHz, η = +0.38) of the ligating histidine nitrogen N δ . From these, we can infer the absolute g tensor orientation with respect to the cluster: The g 2 axis is close to perpendicular to the [2Fe-2S] plane, and g 1 and g 2 are in-plane, but skewed from the Fe-Fe and S-S axes. In X-band ENDOR and ESEEM spectra, a weakly coupled nitrogen is visible, most likely the N ε of the histidine in the protonated state. We find that the cluster is in a valence-localized state, where Fe 2+ is His-bound. The field-sweep spectra show evidence of inter-cluster dipolar coupling that can be simulated using an uncoupled spin model for each cluster (S Fe2+ = 2, S Fe3+ = 5/2). The parameters determined in this work can function as reporters on how the cluster structure is altered upon pH changes and drug binding.
Biochemistry, 2009
The Rieske protein from Thermus thermophilus (TtRp) and a truncated version of the protein (trunc... more The Rieske protein from Thermus thermophilus (TtRp) and a truncated version of the protein (truncTtRp), produced to achieve a low-pH crystallization condition, have been characterized using UV-visible and circular dichroism spectroscopies. TtRp and truncTtRp undergo a change in the UV-visible spectra with increasing pH. The LMCT band at 458 nm shifts to 436 nm and increases in intensity. The increase at 436 nm versus pH can be fit using the sum of two Henderson-Hasselbalch equations, yielding two pK(a) values for the oxidized protein. For TtRp, pK(ox1) = 7.48 +/- 0.12 and pK(ox2) = 10.07 +/- 0.17. For truncTtRp, pK(ox1) = 7.87 +/- 0.17 and pK(ox2) = 9.84 +/- 0.42. The shift to shorter wavelength and the increase in intensity for the LMCT band with increasing pH are consistent with deprotonation of the histidine ligands. A pH titration of truncTtRp monitored by circular dichroism also showed pH-dependent changes at 315 and 340 nm. At 340 nm, the fit gives pK(ox1) = 7.14 +/- 0.26 and pK(ox2) = 9.32 +/- 0.36. The change at 315 nm is best fit for a single deprotonation event, giving pK(ox1) = 7.82 +/- 0.10. The lower wavelength region of the CD spectra was unaffected by pH, indicating that the overall fold of the protein remains unchanged, which is consistent with crystallographic results of truncTtRp. The structure of truncTtRp crystallized at pH 6.2 is very similar to TtRp at pH 8.5 and contains only subtle changes localized at the [2Fe-2S] cluster. These titration and structural results further elucidate the histidine ligand characteristics and are consistent with important roles for these amino acids.
Biochimica et Biophysica Acta (BBA) - Bioenergetics, 2004
The pulsed electron paramagnetic resonance (EPR) methods of electron spin echo envelope modulatio... more The pulsed electron paramagnetic resonance (EPR) methods of electron spin echo envelope modulation (ESEEM) and electron spin echoelectron nuclear double resonance (ESE-ENDOR) are used to investigate the structure of the Photosystem II oxygen-evolving complex (OEC), including the paramagnetic manganese cluster and its immediate surroundings. Recent unpublished results from the pulsed EPR laboratory at UC-Davis are discussed, along with aspects of recent publications, with a focus on substrate and cofactor interactions. New data on the proximity of exchangeable deuterons around the Mn cluster poised in the S 0 -state are presented and interpreted. These pulsed EPR results are used in an evaluation of several recently proposed mechanisms for PSII water oxidation. We strongly favor mechanistic models where the substrate waters bind within the OEC early in the S-state cycle. Models in which the OUO bond is formed by a nucleophilic attack by a Ca 2 + -bound water on a strong S 4 -state electrophile provide a good match to the pulsed EPR data. D
Applied Magnetic Resonance, 2007
Electron paramagnetic resonance studies at multiple frequencies (MF EPR) can provide detailed ele... more Electron paramagnetic resonance studies at multiple frequencies (MF EPR) can provide detailed electronic structure descriptions of unpaired electrons in organic radicals, inorganic complexes, and metalloenzymes. Analysis of these properties aids in the assignment of the chemical environment surrounding the paramagnet and provides mechanistic insight into the chemical reactions in which these systems take part. Herein, we present results from pulsed EPR studies performed at three different frequencies (9, 31, and 130 GHz) on [Mn(II)(H 2 O) 6 ] 2! , Mn(II) adducts with the nucleotides ATP and GMP, and the Mn(II)-bound form of the hammerhead ribozyme (MnHH). Through line shape analysis and interpretation of the zero-field splitting values derived from successful simulations of the corresponding continuous-wave and field-swept echo-detected spectra, these data are used to exemplify the ability of the MF EPR approach in distinguishing the nature of the first ligand sphere. A survey of recent results from pulsed EPR, as well as pulsed electronnuclear double resonance and electron spin echo envelope modulation spectroscopic studies applied to Mn(II)-dependent systems, is also presented.
Analytical Chemistry, 1983
Journal of the American Chemical Society, 2010
Human mitoNEET is a homodimeric iron-sulfur protein located in the outer mitochondrial membrane w... more Human mitoNEET is a homodimeric iron-sulfur protein located in the outer mitochondrial membrane with unknown function, but which is known to interact with thiazolidinedione diabetes drugs. Each monomer houses a [2Fe-2S] cluster with an unusual (Cys) 3 (His) 1 ligation. The His ligand is important for enabling cluster release and for tuning the redox potential. We use multi-frequency (X-, Ka-, Qband) and multi-technique (CW, ESEEM, ENDOR, HYSCORE) EPR spectroscopy to investigate the cluster in its paramagnetic reduced [Fe 2+ Fe 3+ ] (S = 1/2) state. It has a rhombic g-tensor (2.007, 1.937, 1.897) with an average g-value of 1.947 that falls between those of Rieske-type and ferredoxintype [2Fe-2S] clusters. Simulation and least-squares fitting of orientation-selective Ka-and Q-band ENDOR, 1D ESEEM and HYSCORE spectra of 14 N and 15 N-labelled mitoNEET yield the principal values and orientations of both the hyperfine tensor ( 14 N: A iso = −6.25 MHz, T = −0.94 MHz) and the quadrupolar tensor (e 2 Qq/h = −2.47 MHz, η = +0.38) of the ligating histidine nitrogen N δ . From these, we can infer the absolute g tensor orientation with respect to the cluster: The g 2 axis is close to perpendicular to the [2Fe-2S] plane, and g 1 and g 2 are in-plane, but skewed from the Fe-Fe and S-S axes. In X-band ENDOR and ESEEM spectra, a weakly coupled nitrogen is visible, most likely the N ε of the histidine in the protonated state. We find that the cluster is in a valence-localized state, where Fe 2+ is His-bound. The field-sweep spectra show evidence of inter-cluster dipolar coupling that can be simulated using an uncoupled spin model for each cluster (S Fe2+ = 2, S Fe3+ = 5/2). The parameters determined in this work can function as reporters on how the cluster structure is altered upon pH changes and drug binding.