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Observing enzyme ternary transition state analogue complexes by 19F NMR spectroscopy.

ABSTRACT: Ternary transition state analogue (TSA) complexes probing the isomerization of ?-d-glucose 1-phosphate (G1P) into d-glucose 6-phosphate (G6P) catalyzed by catalytically active, fluorinated (5-fluorotryptophan), ?-phosphoglucomutase (?PGM) have been observed directly by 19F NMR spectroscopy. In these complexes MgF3- and AlF4- are surrogates for the transferring phosphate. However, the relevance of these metal fluorides as TSA complexes has been queried. The 1D 19F spectrum of a ternary TSA complex presented a molar equivalence between fluorinated enzyme, metal fluoride and non-isomerizable fluoromethylenephosphonate substrate analogue. Ring flips of the 5-fluoroindole ring remote from the active site were observed by both 19F NMR and X-ray crystallography, but did not perturb function. This data unequivocally demonstrates that the concentration of the metal fluoride complexes is equivalent to the concentration of enzyme and ligand in the TSA complex in aqueous solution.

SUBMITTER: Ampaw A

PROVIDER: S-EPMC5863612 | biostudies-literature | 2017 Dec

REPOSITORIES: biostudies-literature

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Observing enzyme ternary transition state analogue complexes by 19F NMR spectroscopy.

Ampaw Anna A Carroll Madison M von Velsen Jill J Bhattasali Debabrata D Cohen Alejandro A Bowler Matthew W MW Jakeman David L DL

Chemical science 20171023 12

Ternary transition state analogue (TSA) complexes probing the isomerization of β-d-glucose 1-phosphate (G1P) into d-glucose 6-phosphate (G6P) catalyzed by catalytically active, fluorinated (5-fluorotryptophan), β-phosphoglucomutase (βPGM) have been observed directly by 19F NMR spectroscopy. In these complexes MgF3- and AlF4- are surrogates for the transferring phosphate. However, the relevance of these metal fluorides as TSA complexes has be ...[more]

PMID: 29619190

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Project description:(51)V solid-state NMR (SSNMR) studies of a series of noninnocent vanadium(V) catechol complexes have been conducted to evaluate the possibility that (51)V NMR observables, quadrupolar and chemical shift anisotropies, and electronic structures of such compounds can be used to characterize these compounds. The vanadium(V) catechol complexes described in these studies have relatively small quadrupolar coupling constants, which cover a surprisingly small range from 3.4 to 4.2 MHz. On the other hand, isotropic (51)V NMR chemical shifts cover a wide range from -200 to 400 ppm in solution and from -219 to 530 ppm in the solid state. A linear correlation of (51)V NMR isotropic solution and solid-state chemical shifts of complexes containing noninnocent ligands is observed. These experimental results provide the information needed for the application of (51)V SSNMR spectroscopy in characterizing the electronic properties of a wide variety of vanadium-containing systems and, in particular, those containing noninnocent ligands and that have chemical shifts outside the populated range of -300 to -700 ppm. The studies presented in this report demonstrate that the small quadrupolar couplings covering a narrow range of values reflect the symmetric electronic charge distribution, which is also similar across these complexes. These quadrupolar interaction parameters alone are not sufficient to capture the rich electronic structure of these complexes. In contrast, the chemical shift anisotropy tensor elements accessible from (51)V SSNMR experiments are a highly sensitive probe of subtle differences in electronic distribution and orbital occupancy in these compounds. Quantum chemical (density functional theory) calculations of NMR parameters for [VO(hshed)(Cat)] yield a (51)V chemical shift anisotropy tensor in reasonable agreement with the experimental results, but surprisingly the calculated quadrupolar coupling constant is significantly greater than the experimental value. The studies demonstrate that substitution of the catechol ligand with electron-donating groups results in an increase in the HOMO-LUMO gap and can be directly followed by an upfield shift for the vanadium catechol complex. In contrast, substitution of the catechol ligand with electron-withdrawing groups results in a decrease in the HOMO-LUMO gap and can directly be followed by a downfield shift for the complex. The vanadium catechol complexes were used in this work because (51)V is a half-integer quadrupolar nucleus whose NMR observables are highly sensitive to the local environment. However, the results are general and could be extended to other redox-active complexes that exhibit coordination chemistry similar to that of the vanadium catechol complexes.

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Observing enzyme ternary transition state analogue complexes by 19F NMR spectroscopy.

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Observing enzyme ternary transition state analogue complexes by <sup>19</sup>F NMR spectroscopy.

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