Coupling of functional hydrogen bonds in pyridoxal-5′-phosphate- enzyme model systems observed by solid-state NMR spectroscopy

Shasad Sharif, David Schagen, Michael D. Toney, Hans Heinrich Limbach

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Abstract

We present a novel series of hydrogen-bonded, polycrystalline 1:1 complexes of Schiff base models of the cofactor pyridoxal-5′-phosphate (PLP) with carboxylic acids that mimic the cofactor in a variety of enzyme active sites. These systems contain an intramolecular OHN hydrogen bond characterized by a fast proton tautomerism as well as a strong intermolecular OHN hydrogen bond between the pyridine ring of the cofactor and the carboxylic acid. In particular, the aldenamine and aldimine Schiff bases N-(pyridoxylidene) tolylamine and N-(pyridoxylidene)methylamine, as well as their adducts, were synthesized and studied using 15N CP and 1H NMR techniques under static and/or MAS conditions. The geometries of the hydrogen bonds were obtained from X-ray structures, 1H and 15N chemical shift correlations, secondary H/D isotope effects on the 15N chemical shifts, or directly by measuring the dipolar 2H-15N couplings of static samples of the deuterated compounds. An interesting coupling of the two "functional" OHN hydrogen bonds was observed. When the Schiff base nitrogen atoms of the adducts carry an aliphatic substituent such as in the internal and external aldimines of PLP in the enzymatic environment, protonation of the ring nitrogen shifts the proton in the intramolecular OHN hydrogen bond from the oxygen to the Schiff base nitrogen. This effect, which increases the positive charge on the nitrogen atom, has been discussed as a prerequisite for cofactor activity. This coupled proton transfer does not occur if the Schiff base nitrogen atom carries an aromatic substituent.

Original languageEnglish (US)
Pages (from-to)4440-4455
Number of pages16
JournalJournal of the American Chemical Society
Volume129
Issue number14
DOIs
StatePublished - Apr 11 2007

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Pyridoxal Phosphate
Schiff Bases
Nuclear magnetic resonance spectroscopy
Hydrogen
Hydrogen bonds
Phosphates
Magnetic Resonance Spectroscopy
Nitrogen
Enzymes
Protons
Chemical shift
Carboxylic Acids
Carboxylic acids
Atoms
Proton transfer
Protonation
Isotopes
Pyridine
Nuclear magnetic resonance
Catalytic Domain

ASJC Scopus subject areas

  • Chemistry(all)

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Coupling of functional hydrogen bonds in pyridoxal-5′-phosphate- enzyme model systems observed by solid-state NMR spectroscopy. / Sharif, Shasad; Schagen, David; Toney, Michael D.; Limbach, Hans Heinrich.

In: Journal of the American Chemical Society, Vol. 129, No. 14, 11.04.2007, p. 4440-4455.

Research output: Contribution to journalArticle

Sharif, Shasad ; Schagen, David ; Toney, Michael D. ; Limbach, Hans Heinrich. / Coupling of functional hydrogen bonds in pyridoxal-5′-phosphate- enzyme model systems observed by solid-state NMR spectroscopy. In: Journal of the American Chemical Society. 2007 ; Vol. 129, No. 14. pp. 4440-4455.
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