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 Differentiation of the binding of two ligands to a tetrameric protein with a single symmetric active site by 19F NMR |
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Dec 12, 2020 - 6:54 PM - by nmrlearner
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Differentiation of the binding of two ligands to a tetrameric protein with a single symmetric active site by 19F NMR
Abstract
R67 dihydrofolate reductase (R67 DHFR) is a plasmid-encoded enzyme that confers resistance to the antibacterial drug trimethoprim. R67 DHFR is a tetramer with a single active site that is unusual as both cofactor and substrate are recognized by symmetry-related residues. Such promiscuity has limited our previous efforts to differentiate ligand binding by NMR. To address this problem, we incorporated fluorine at positions 4, 5, 6, or 7 of the indole rings of tryptophans 38 and 45 and characterized the spectra to determine which probe was optimal for studying ligand binding. Two resonances were observed for all apo proteins. Unexpectedly, the W45 resonance appeared broad, and truncation of the disordered N-termini resulted in the appearance of one sharp W45 resonance. These results are consistent with interaction of the N-terminus with W45. Binding of the cofactor broadened W38 for all fluorine probes, whereas substrate, dihydrofolate, binding resulted in the appearance of three new resonances for 4- and 5-fluoroindole labeled protein and severe line broadening for 6- and 7-fluoroindole R67 DHFR. W45 became slightly broader upon ligand binding. With only two peaks in the 19F NMR spectra, our data were able to differentiate cofactor and substrate binding to the single, symmetric active site of R67 DHFR and yield binding affinities.
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[NMR paper] Dominant entropic binding of perfluoroalkyl substances (PFASs) to albumin protein revealed by 19F NMR. |
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Dec 12, 2020 - 6:54 PM - by nmrlearner
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Dominant entropic binding of perfluoroalkyl substances (PFASs) to albumin protein revealed by 19F NMR.
Related Articles Dominant entropic binding of perfluoroalkyl substances (PFASs) to albumin protein revealed by 19F NMR.
Chemosphere. 2021 Jan;263:128083
Authors: Fedorenko M, Alesio J, Fedorenko A, Slitt A, Bothun GD
Abstract
Mechanistic insight into protein binding by poly- and perfluoroalkyl substances (PFASs) is critical to understanding how PFASs distribute and accumulate within the body and to developing predictive models within and across classes of PFASs. Fluorine nuclear magnetic resonance spectroscopy (19F NMR) has proven to be a powerful, yet underutilized tool to study PFAS binding; chemical shifts of each fluorine group reflect the local environment along the length of the PFAS molecule. Using bovine serum albumin (BSA), we report dissociation constants, Kd, for four common PFASs well below reported critical micelle concentrations (CMCs)*-*perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), perfluorohexanesulfonic acid (PFHxS), and perfluorooctanesulfonic acid (PFOS)*-*as a function of temperature in phosphate buffered saline. Kd values were determined based on the difluoroethyl group adjacent to the anionic headgroups and the terminal trifluoromethyl groups. Our results indicate that the hydrophobic tails exhibit greater binding affinity relative to the headgroup, and that the binding affinities are generally consistent with previous results... [Read More]
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0 Replies | 12 Views
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