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(delta1)-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(delta1)-H proton and its covalently attached N(delta1)-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(delta1)-H proton and its covalently attached N(delta1)-nitrogen. The sensitivity of detection for the short-lived N(delta1)-H proton was enhanced substantially by improved water suppression, in particular, the suppression of radiation damping via pulsed field gradients.

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