Direct NMR resonance assignments of the active site histidine residue in Escherichia coli thioesterase I/protease I/lysophospholipase L₁

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 L₁ (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.