Heteronuclear proton assisted recoupling
- 1 March 2011
- journal article
- research article
- Published by AIP Publishing in The Journal of Chemical Physics
- Vol. 134 (9), 095101
- https://doi.org/10.1063/1.3541251
Abstract
We describe a theoretical framework for understanding the heteronuclear version of the third spin assisted recoupling polarization transfer mechanism and demonstrate its potential for detecting long-distance intramolecular and intermolecular 15N–13C contacts in biomolecular systems. The pulse sequence, proton assisted insensitive nuclei cross polarization (PAIN-CP) relies on a cross term between 1H–15N and 1H–13C dipolar couplings to mediate zero- and/or double-quantum 15N–13C recoupling. In particular, using average Hamiltonian theory we derive effective Hamiltonians for PAIN-CP and show that the transfer is mediated by trilinear terms of the form N±C∓Hz (ZQ) or N±C±Hz (DQ) depending on the rf field strengths employed. We use analytical and numerical simulations to explain the structure of the PAIN-CP optimization maps and to delineate the appropriate matching conditions. We also detail the dependence of the PAIN-CP polarization transfer with respect to local molecular geometry and explain the observed reduction in dipolar truncation. In addition, we demonstrate the utility of PAIN-CP in structural studies with 15N–13C spectra of two uniformly 13C,15N labeled model microcrystalline proteins—GB1, a 56 amino acid peptide, and Crh, a 85 amino acid domain swapped dimer (MW = 2 × 10.4 kDa). The spectra acquired at high magic angle spinning frequencies (ωr/2π > 20 kHz) and magnetic fields (ω0H/2π = 700–900 MHz) using moderate rf fields, yield multiple long-distance intramonomer and intermonomer 15N–13C contacts. We use these distance restraints, in combination with the available x-ray structure as a homology model, to perform a calculation of the monomer subunit of the Crh protein.Keywords
Funding Information
- National Institutes of Health (ANR08-CEXC-003-01, EB-002026, EB-003151, JC05_44957)
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