Characterization of different water pools in solid-state NMR protein samples.
We observed and characterized two distinct signals originating from different pools of water protons in solid-state NMR protein samples, namely from crystal water which exchanges polarization with the protein (on the NMR timescale) and is located in the protein-rich fraction at the periphery of the magic-angle spinning (MAS) sample container, and supernatant water located close to the axis of the sample container. The polarization transfer between the water and the protein can be probed by two-dimensional exchange spectroscopy, and we show that the supernatant water does not interact with protein on the timescale of the experiments. The two water pools have different spectroscopic properties, including resonance frequency, longitudinal, transverse and rotating frame relaxation times. The supernatant water can be removed almost completely physically or can be frozen selectively. Both measures lead to an enhancement of the quality factor of the probe circuit, accompanied by an improvement of the experimental signal/noise, and greatly simplify solvent-suppression by substantially reducing the water signal. We also present a tool, which allows filling solid-state NMR sample containers in a more efficient manner, greatly reducing the amount of supernatant water and maximizing signal/noise.
Institut de Biologie et Chimie des Protéines, Université de Lyon, UMR 5086 CNRS/UCB-Lyon 1, 7 passage du Vercors, 69367 Lyon, France. a.bockmann@ibcp.fr
Anja
A
Böckmann
Carole
C
Gardiennet
René
R
Verel
Andreas
A
Hunkeler
Antoine
A
Loquet
Guido
G
Pintacuda
Lyndon
L
Emsley
Beat H
BH
Meier
Anne
A
Lesage
D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D011506:Proteins / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
D011506:Proteins; D014867:Water