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Analytical Chemistry

Magnetic Doping Speeds Up Protein NMR

Adding a paramagnetic copper complex to protein samples decreases the recycle time between pulses in solid-state NMR

by Celia Henry Arnaud
February 16, 2009 | A version of this story appeared in Volume 87, Issue 7

Data collection in two-dimensional 13C solid-state NMR is slowed down by the need for atoms in the sample to recover their usual proton spin polarization between scans. Yoshitaka Ishii and coworkers at the University of Illinois, Chicago, have now shortened this recovery time and improved the speed and sensitivity of 2-D solid-state NMR by spiking protein samples with a paramagnetic dopant, copper(II) ethylenediaminetetraacetic acid (Nat. Methods, DOI: 10.1038/nmeth.1300). The spectra of doped and undoped samples are almost identical in terms of intensities and chemical shifts. But the dopant reduces the proton longitudinal relaxation time of the proteins and allows the researchers to repeat NMR pulse sequences more quickly. Ishii and coworkers call their new method paramagnetic relaxation-assisted condensed data collection (PACC). They used PACC to obtain spectra of nanomole quantities of ubiquitin and β-amyloid fibrils, the latter of which are associated with Alzheimer's disease. In the case of ubiquitin, the dopant decreased the relaxation time from 230 milliseconds to 50 milliseconds and shortened the time for data collection from 21.9 hours to 5.4 hours.


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