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Updated: Jun 10, 2026

Atomic Scale Structural Studies of Macromolecular Assemblies by Solid-state Nuclear Magnetic Resonance Spectroscopy
Published on: September 17, 2017
Application of multiple-quantum line narrowing with simultaneous 1H and 13C constant-time scalar-coupling evolution
G V Swapna1, C B Rios, Z Shang
1Center for Advanced Biotechnology and Medicine and Department of Molecular Biology and Biochemistry, Rutgers University, 679 Hoes Lane, Piscataway, NJ, 08854-5638, U.S.A.
Abstract:
Many triple-resonance experiments make use of one-bond heteronuclear scalar couplings toestablish connectivities among backbone and/or side-chain nuclei. In medium-sized(15-30 kDa) proteins, short transverse relaxation times of Calpha single-quantum stateslimit signal-to-noise (S/N) ratios. These relaxation properties can be improved usingheteronuclear multiple-quantum coherences (HMQCs) instead of heteronuclear single-quantumcoherences (HSQCs) in the pulse sequence design. In slowly tumbling macromolecules, theseHMQCs can exhibit significantly better transverse relaxation properties than HSQCs.However, HMQC-type experiments also exhibit resonance splittings due to multiple two- andthree-bond homo- and heteronuclear scalar couplings. We describe here a family of pulsed-field gradient (PFG) HMQC-type triple-resonance experiments using simultaneous 1H and13C constant-time (CT) periods to eliminate the t1 dependence of these scalar couplingeffects. These simultaneous CT PFG-(HA)CANH and PFG-(HA)CA(CO)NH HMQC-typeexperiments exhibit sharper resonance line widths and often have better S/N ratios than thecorresponding HSQC-type experiments. Results on proteins ranging in size from 6 to 30 kDashow average methine CalphaH HMQC:HSQC enhancement factors of 1.10 +/- 0.15, withabout 40% of the cross peaks exhibiting better S/N ratios in the simultaneous CT-HMQCversions compared with the HSQC versions.
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