Using the water signal to detect invisible exchanging protons in the catalytic triad of a serine protease.

ABSTRACT: Chemical Exchange Saturation Transfer (CEST) is an MRI approach that can indirectly detect exchange broadened protons that are invisible in traditional NMR spectra. We modified the CEST pulse sequence for use on high-resolution spectrometers and developed a quantitative approach for measuring exchange rates based upon CEST spectra. This new methodology was applied to the rapidly exchanging Hδ1 and Hε2 protons of His57 in the catalytic triad of bovine chymotrypsinogen-A (bCT-A). CEST enabled observation of Hε2 at neutral pH values, and also allowed measurement of solvent exchange rates for His57-Hδ1 and His57-Hε2 across a wide pH range (3-10). Hδ1 exchange was only dependent upon the charge state of the His57 (k (ex,Im+) = 470 s(-1), k (ex,Im) = 50 s(-1)), while Hε2 exchange was found to be

SUBMITTER: Lauzon CB 

PROVIDER: S-EPMC3149851 | biostudies-literature | 2011 Aug

REPOSITORIES: biostudies-literature