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

Protein Sci. 1998 Mar;7(3):789-93. doi: 10.1002/pro.5560070329.


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.

MeSH terms

  • Bacterial Proteins / chemistry
  • Binding Sites
  • Escherichia coli / enzymology*
  • Histidine / chemistry
  • Models, Molecular
  • Nuclear Magnetic Resonance, Biomolecular
  • Phosphoenolpyruvate Sugar Phosphotransferase System / chemistry*
  • Phosphorylation
  • Protein Structure, Tertiary


  • Bacterial Proteins
  • Histidine
  • Phosphoenolpyruvate Sugar Phosphotransferase System