scholarly journals Significance of Conformation Changes During the Binding and Release of Chromium(III) from Human Serum Transferrin

2020 ◽  
Vol 4 (Supplement_2) ◽  
pp. 1798-1798
Author(s):  
Kyle Edwards ◽  
John Vincent
Keyword(s):  
Metal Binding ◽  
Spectroscopic Properties ◽  
Spectroscopic Studies ◽  
Turnover Time ◽  
Time Intervals ◽  
Paramagnetic Resonance ◽  
Funding Sources ◽  
Research Award ◽  
Conformation Changes ◽  
Multiple Conformations

Abstract Objectives Transferrin, Tf, the protein that transports iron from the blood to the tissues via endocytosis, is believed to also transport chromium(III), Cr(III). Recently, the presence of multiple conformations was suggested by spectroscopic studies. The objective of this work is confirm whether various conformers of Cr(III)2-Tf exist and their potential significance for Cr(III) transport. Methods Cr(III) was added to apoTf in a buffered solution at pH 7.4 containing 25 mM bicarbonate at 37 °C. After time intervals, ultraviolet spectra were collected, or aliquots were removed and frozen for analysis by electron paramagnetic resonance (EPR) spectroscopy, which can distinguish free Cr(III) and Cr(III) bound to the two metal binding sites of Tf. To model the acidification of the endosome that triggers release of metal ions from Tf, the Cr(III)2-Tf conformer solutions were acidified by the addition of hydrochloric acid to pH 4.5 or 5.5. At time intervals after acidification, samples were again analyzed by ultraviolet and EPR spectroscopies. Results A combination of electronic and EPR studies reveal that the addition of Cr(III) to apoTf at near neutral pH in the presence of 25 mM bicarbonate results in the rapid binding of two Cr(III) accompanied and then followed by a series of conformation changes in Cr(III)2-Tf. These multiple conformations give rise to different spectroscopic properties and upon acidification different rates of Cr(III) release. Conclusions The conformer of Cr(III)2-Tf used in most previous studies and giving rise to EPR features at g ∼ 5.1, 5.4, and 5.6 forms too slowly to be physiologically relevant; however, two previously unknown conformers of Cr(III)2-Tf, giving rise to an EPR feature at g ∼2 and at g ∼ 5.4, respectively, were identified. The latter of these conformers has a lifespan similar to the turnover time of transferrin and releases Cr(III) rapidly, suggesting it is probably the most physiologically significant conformer of Cr(III)2-Tf. Funding Sources The University of Alabama College of Arts and Sciences Research Award.

scholarly journals Binding of Cr2-transferrin to Transferrin Receptor Enhances the Rate of Chromium Loss and Is Dependent on the Conformation of Transferrin (P24-053-19)

2019 ◽  
Vol 3 (Supplement_1) ◽  
Author(s):  
Kyle Edwards ◽  
Hannah Kim ◽  
Cortlyn Boyd ◽  
John Vincent
Keyword(s):  
Metal Binding ◽  
Transferrin Receptor ◽  
Binding Sites ◽  
Blood Stream ◽  
Time Intervals ◽  
Paramagnetic Resonance ◽  
Physiological Conditions ◽  
Metal Binding Sites ◽  
Funding Sources ◽  
Research Award

Abstract Objectives Transferrin, Tf, the protein transports iron from the blood to the tissues via endocytosis, is believed to also transport chromium(III), Cr(III). Recently, the release of Cr(III) from Tf has been postulated to be too slow for appreciable quantities of Cr(III) to be released during the lifetime of an endosome. The objective of this work was to measure the rate of Cr(III) release from human serum Tf as a function of Tf confirmation and as the transferrin-transferrin receptor (TfR) complex. Methods Cr(III) was added to apoTf in a buffered solution at pH 7.4 containing 25 mM bicarbonate at 37 °C. After time intervals, ultraviolet spectra were collected, or aliquots were removed and frozen for analysis by electron paramagnetic resonance (EPR) spectroscopy, which can distinguish free Cr(III) and Cr(III) bound to the two metal binding sites of Tf. To model the acidification of the endosome that triggers release of metal ions from Tf, the Cr(III)2-Tf solutions were acidified by the addition of hydrochloric acid to pH 4.5 or 5.5. At time intervals after acidification, samples were again analyzed by ultraviolet and EPR spectroscopies. Similar studies were performed in the presence of Tf receptor, which binds two equivalents of Cr(III)2-Tf. Results The loss of Cr(III) from the two metal-binding sites of Tf occur at different rates. Different confirmations of the Cr2-Tf complex exist depending on the conditions of Cr2-Tf formation. The conformation that forms rapidly under physiological conditions loses Cr(III) faster than conformations that form over longer periods of time. Binding of Cr(III)2-Tf to TfR facilitates the release of Cr. Conclusions The conformation of Cr(III)2-transferrin that forms under physiological conditions when complexed with transferrin receptor can release Cr at physiologically significant rates consistent with transferrin serving as the major Cr(III) transport agent between the blood stream and tissues. Funding Sources The University of Alabama College of Arts and Sciences Research Award.

scholarly journals X-ray Crystal Structure of Dichromium-transferrin with Synergistic Anion Malonate (P24-061-19)

2019 ◽  
Vol 3 (Supplement_1) ◽  
Author(s):  
John Vincent ◽  
Kyle Edwards ◽  
Courtney Petersen ◽  
Nathaniel Gilbert ◽  
Matthew Thompson
Keyword(s):  
Metal Ions ◽  
Binding Site ◽  
Metal Binding ◽  
Diffusion Method ◽  
Metal Binding Site ◽  
Funding Sources ◽  
Research Award ◽  
Crystallization Conditions ◽  
Unit Cell Dimensions ◽  
The University

Abstract Objectives Transferrin, Tf, the protein that transports iron, as Fe(III) from the blood to the tissues via endocytosis, is believed to also transport chromium(III), Cr(III). Under physiological conditions, transferrin binds Fe(III) and Cr(III), but can bind other metal ions such as titanium(IV), Ti(IV), such as in the blood of patients with Ti-containing implants. Questions have arisen whether similar protein and non-protein ligands are bound to the alternative metal ions in transferrin. Methods Human serum Cr(III)2-Tf was prepared in a buffered solution at pH 7.4 containing 25 mM bicarbonate at 37°C. The hanging drop vapor diffusion method was used for crystallization. The crystallization conditions contained 100 mM Hepes (pH 7.0, 20 mM disodium malonate, 14% PEG3350, 20% glycerol, and 55 mg/mL transferrin. Results Cr(III)2-Tf crystallized in the space group C2221 with unit cell dimensions a = 137.05 Å, b = 158.01 Å, and c = 107.14 Å and α = β = γ = 90°. The C-terminal lobe is in the closed confirmation, while the N-terminal lobe is in the open confirmation. The C-terminal metal-binding site has four protein-provided ligands (two tyrosines, one histidine, and one aspartate) to the Cr(III) center, while six coordination is completed by two oxygens from a malonate anion. Thus, under the crystallization conditions, malonate displaces `the synergistic bicarbonate anion normally at the metal-binding site. The N-terminal metal binding site possesses only one protein-provided ligand (tyrosine) while the other binding sites about the Cr(III) center are filled by a (bi)carbonate anion and water molecules. Conclusions Under the conditions of crystallization, the C-terminal lobe of transferrin binds Cr(III) in a similar fashion to Fe(III) and Ti(IV), although the ligation at the N-terminal binding site varies. These similarities and differences in coordination have implications for the relative ability of transferrin to bind and release Fe, Cr, and Ti. Funding Sources The University of Alabama College of Arts and Sciences Research Award.

Optical Spectroscopic Studies of a Soluble Fluorene-Based Conjugated Polymer: A Hydrostatic Pressure and Temperature Study

2001 ◽  
Vol 708 ◽  
Author(s):  
S. Guha ◽  
J.D. Rice ◽  
C. M. Martin ◽  
W. Graupner ◽  
M. Chandrasekhar ◽  
...  
Keyword(s):  
Hydrostatic Pressure ◽  
Conjugated Polymer ◽  
Spectroscopic Properties ◽  
Spectroscopic Studies ◽  
Phonon Interaction ◽  
Optical Studies ◽  
Strong Electron ◽  
Conjugated Molecules ◽  
Electron Phonon Interaction ◽  
Backbone Conformation

ABSTRACTSpectroscopic properties of conjugated molecules/polymers have varying degrees of sensitivity to backbone conformation. Optical studies are presented as a function of temperature and hydrostatic pressure, using photoluminescence and Raman scattering from two polymers with distinct differences in their backbone conformation, namely, polyfluorene (PF) and ladder type poly(para-phenylene)(m-LPPP). In contrast to the photoluminescence (PL) vibronics in mLPPP, the 0-0 PL vibronic peak in PF shows a red-shift with increasing temperatures. Pressure studies reveal that the PL spectrum of PF red-shifts and broadens with increasing pressures. The phonon lines in PF show an antiresonance effect at higher pressures indicating a strong electron-phonon interaction.

scholarly journals Redox-State Dependent Spectroscopic Properties of Porous Organic Polymers Containing Furan, Thiophene, and Selenophene

2017 ◽  
Vol 70 (11) ◽  
pp. 1227 ◽  
Author(s):  
Carol Hua ◽  
Stone Woo ◽  
Aditya Rawal ◽  
Floriana Tuna ◽  
James M. Hook ◽  
...  
Keyword(s):  
Solid State ◽  
Redox State ◽  
Spectroscopic Properties ◽  
Structural Features ◽  
Organic Polymers ◽  
Stimuli Responsive ◽  
Porous Organic Polymers ◽  
Paramagnetic Resonance ◽  
Responsive Materials ◽  
State Dependent

A series of electroactive triarylamine porous organic polymers (POPs) with furan, thiophene, and selenophene (POP-O, POP-S, and POP-Se) linkers have been synthesised and their electronic and spectroscopic properties investigated as a function of redox state. Solid state NMR provided insight into the structural features of the POPs, while in situ solid state Vis-NIR and electron paramagnetic resonance spectroelectrochemistry showed that the distinct redox states in POP-S could be reversibly accessed. The development of redox-active porous organic polymers with heterocyclic linkers affords their potential application as stimuli responsive materials in gas storage, catalysis, and as electrochromic materials.

scholarly journals Characterizing SPASM/twitch Domain-Containing Radical SAM Enzymes by EPR Spectroscopy

2021 ◽  
Author(s):  
Aidin R. Balo ◽  
Lizhi Tao ◽  
R. David Britt
Keyword(s):  
Epr Spectroscopy ◽  
Continuous Wave ◽  
Spectroscopic Studies ◽  
Paramagnetic Species ◽  
Paramagnetic Resonance ◽  
Iron Sulfur Cluster ◽  
Radical Sam Enzymes ◽  
Iron Sulfur ◽  
Pulse Epr ◽  
Multiple Domains

AbstractOwing to their importance, diversity and abundance of generated paramagnetic species, radical S-adenosylmethionine (rSAM) enzymes have become popular targets for electron paramagnetic resonance (EPR) spectroscopic studies. In contrast to prototypic single-domain and thus single-[4Fe–4S]-containing rSAM enzymes, there is a large subfamily of rSAM enzymes with multiple domains and one or two additional iron–sulfur cluster(s) called the SPASM/twitch domain-containing rSAM enzymes. EPR spectroscopy is a powerful tool that allows for the observation of the iron–sulfur clusters as well as potentially trappable paramagnetic reaction intermediates. Here, we review continuous-wave and pulse EPR spectroscopic studies of SPASM/twitch domain-containing rSAM enzymes. Among these enzymes, we will review in greater depth four well-studied enzymes, BtrN, MoaA, PqqE, and SuiB. Towards establishing a functional consensus of the additional architecture in these enzymes, we describe the commonalities between these enzymes as observed by EPR spectroscopy.

The magnetic and spectroscopic properties of certain rare-earth double nitrates

1955 ◽  
Vol 232 (1191) ◽  
pp. 458-474 ◽  
Keyword(s):  
Rare Earth ◽  
Electric Field ◽  
Spectroscopic Properties ◽  
Rare Earth Ions ◽  
Rare Earth Ion ◽  
Crystalline Electric Field ◽  
Paramagnetic Resonance ◽  
Systematic Fashion ◽  
Resonance Data ◽  
Rare Earth Series

The theory that has been developed for rare-earth ions in crystals is here applied to the double nitrates. The paramagnetic resonance data and certain spectroscopic properties of the different rare-earth double nitrates, depending as they do on the crystalline electric field at a rare-earth ion, are related to the six parameters through which the field is defined. It is found that most of the experimental results can be fitted to values of the parameters that vary in a systematic fashion along the rare-earth series.

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