Accurate Quantitation of Water-amide Proton Exchange Rates Using the Phase-Modulated CLEAN Chemical EXchange (CLEANEX-PM) Approach with a Fast-HSQC (FHSQC) Detection Scheme |
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| Authors: | Tsang-Lin Hwang Peter C.M. van Zijl Susumu Mori |
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| Affiliation: | (1) Department of Radiology, School of Medicine, Johns Hopkins University, 217 Traylor Building, 720 Rutland Avenue, Baltimore, MD, 21205-2195, U.S.A;(2) Department of Biophysics and Biophysical Chemistry, School of Medicine, Johns Hopkins University, 217 Traylor Building, 720 Rutland Avenue, Baltimore, MD, 21205-2195, U.S.A |
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| Abstract: | Measurement of exchange rates between water and NH protons by magnetization transfer methods is often complicated by artifacts, such as intramolecular NOEs, and/or TOCSY transfer from C protons coincident with the water frequency, or exchange-relayed NOEs from fast exchanging hydroxyl or amine protons. By applying the Phase-Modulated CLEAN chemical EXchange (CLEANEX-PM) spin-locking sequence, 135°(x) 120°(-x) 110°(x) 110°(-x) 120°(x) 135°(-x) during the mixing period, these artifacts can be eliminated, revealing an unambiguous water-NH exchange spectrum. In this paper, the CLEANEX-PM mixing scheme is combined with Fast-HSQC (FHSQC) detection and used to obtain accurate chemical exchange rates from the initial slope analysis for a sample of 15N labeled staphylococcal nuclease. The results are compared to rates obtained using Water EXchange filter (WEX) II-FHSQC, and spin-echo-filtered WEX II-FHSQC measurements, and clearly identify the spurious NOE contributions in the exchange system. |
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| Keywords: | CLEANEX-PM hydrogen exchange NOE protein pulsed field gradients water |
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