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¹³CHD₂ Methyl Group Probes of Millisecond Time Scale Exchange in Proteins by ¹H Relaxation Dispersion: An Application to Proteasome Gating Residue Dynamics


Andrew J. Baldwin, Tomasz L. Religa, D. Flemming Hansen, Guillaume Bouvignies and Lewis E. Kay*
Departments of Molecular Genetics, Biochemistry and Chemistry, The University of Toronto, Toronto, Ontario, M5S 1A8, Canada





Abstract:

A pulse scheme is presented for quantifying millisecond time scale chemical exchange processes in proteins by measuring ¹H CPMG relaxation dispersion profiles of ¹³CHD₂ methyl groups. The use of ¹³CHD₂ isotopomers for ¹H methyl dispersion experiments eliminates problems with interconversion between differentially relaxing proton transitions that complicate the extraction of accurate exchange parameters when ¹³CH₃ probes are used. Good agreement is demonstrated between extracted chemical shift differences from fits of dispersion profiles and the corresponding differences measured independently on a model exchanging system, validating the experiment. The methodology is applied to the gating residues of the T. acidiphilium proteasome that are shown to undergo extensive motion on the millisecond time scale.



Journal of the American Chemical Society, Volume 132, Issue 32, Page 10992-10995, August 18, 2010.

Source: JACS