Direct NMR resonance assignments of the active site histidine residue in Escherichia coli thioesterase I/protease I/lysophospholipase L 1

Owing to the hydrogen‐bond interaction and rapid exchange rate with the bulk water, the transverse relaxation time for the N δ1 H proton of the catalytic histidine in Escherichia coli thioesterase I/protease I/lysophospholipase L 1 (TEP‐I) is rather short. Because of its catalytic importance, it is desirable to detect and assign this proton resonance. In this paper, we report the first direct NMR correlation between the short‐lived N δ1 H proton and its covalently attached N δ1 –nitrogen of the catalytic His157 residue in E. coli thioesterase/protease I. We have used gradient‐enhanced jump‐return spin‐echo HMQC (GE‐JR SE HMQC) to obtain a direct correlation between the short‐lived N δ1 H proton and its covalently attached N δ1 –nitrogen. The sensitivity of detection for the short‐lived N δ1 H proton was enhanced substantially by improved water suppression, in particular, the suppression of radiation damping via pulsed field gradients. Copyright © 2006 John Wiley & Sons, Ltd.