[NMR paper] NMR Signal Quenching from Bound Biradical Affinity Reagents in DNP Samples.

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NMR Signal Quenching from Bound Biradical Affinity Reagents in DNP Samples.

Related Articles NMR Signal Quenching from Bound Biradical Affinity Reagents in DNP Samples.

J Phys Chem B. 2017 Nov 08;:

Authors: Rogawski RT, Sergeyev IV, Zhang Y, Tran TH, Li Y, Tong L, McDermott AE

Abstract
We characterize the effect of specifically bound biradicals on the NMR spectra of dihydrofolate reductase (DHFR) from E. coli. Dynamic nuclear polarization methods enhance the signal-to-noise of solid state NMR experiments by transferring polarization from unpaired electrons of biradicals to nuclei. There has been recent interest in co-localizing the paramagnetic polarizing agents with the analyte of interest through covalent or non-covalent specific interactions. This experimental approach broadens the scope of dynamic nuclear polarization methods by offering the possibility of selective signal enhancements and the potential to work in a broad range of environments. Paramagnetic compounds can have other effects on the NMR spectroscopy of nearby nuclei, including broadening of nuclear resonances due to the proximity of the paramagnetic agent. Understanding the distance dependence of these interactions is important for the success of the technique. Here we explore paramagnetic signal quenching due to a bound biradical, specifically a biradical-derivatized trimethoprim ligand of E. coli dihydrofolate reductase. Biradical-derivatized trimethoprim has nanomolar affinity for DHFR, and affords strong and selective signal enhancements in DNP experiments. In this work, we show that although the TMP fragment is well ordered, the biradical (TOTAPOL) moiety is disordered when bound to the protein due to the flexibility of the linker. The distance dependence in bleaching of NMR signal intensity allows us to detect numerous NMR signals in the protein. We present the possibility that static disorder, and electron spin diffusion play roles in this observation, among other contributions. The fact that the majority of signals are observed strengthens the case for the use of high affinity or covalent radicals in solid state NMR enhancement.


PMID: 29116793 [PubMed - as supplied by publisher]



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