Tautomeric state and pKa of the phosphorylated active site histidine in the N-terminal domain of enzyme I of the Escherichia coli phosphoenolpyruvate:sugar phosphotransferase system. |
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Authors: | D. S. Garrett Y. J. Seok A. Peterkofsky G. M. Clore A. M. Gronenborn |
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Affiliation: | Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892-0520, USA. |
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Abstract: | The phosphorylated form of the N-terminal domain of enzyme I of the phosphoenolpyruvate:sugar phosphotransferase system of Escherichia coli has been investigated by one-bond and long-range 1H-15N correlation spectroscopy. The active site His 189 is phosphorylated at the Nepsilon2 position and has a pKa of 7.3, which is one pH unit higher than that of unphosphorylated His 189. Because the neutral form of unphosphorylated His 189 is in the Ndelta1-H tautomer, and its Nepsilon2 atom is solvent inaccessible and accepts a hydrogen bond from the hydroxyl group of Thr 168, both protonation and phosphorylation of His 189 must be accompanied by a change in the side-chain conformation of His 189, specifically from a chi(2) angle in the g+ conformer in the unphosphorylated state to the g- conformer in the phosphorylated state. |
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Keywords: | histidine phosphorylation N-terminal domain of enzyme I pKa tautomeric state |
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