Solution NMR

The NMRFAM user program provides access to 11 NMR spectrometers (500 MHz – 900 MHz) equipped for a variety of solution and solid-state NMR experiments. A 1.1 GHz solid-state NMR spectrometer is scheduled to arrive in 2023. NMRFAM staff scientists provide advice and assistance in experimental design, data acquisition and processing for studies of molecular structure, dynamics and interactions. We have experience with a range of sample types, including soluble and membrane proteins, fibrils, RNA, small molecules, and metabolomics.

Solution NMR can be used to determine molecular structures, measure molecular motion on a wide range of timescales from picoseconds to hours, and detect molecular interactions. The flexibility of NMR to address a wide range of scientific questions and ability to directly correlate different types of data with specific sites across a molecule is a major strength. However, the breadth of NMR applications can also make experimental design a challenge for those who are not familiar with the technology. The sections below provide an overview of NMRFAM capabilities and sample considerations for different types of applications.

Experiments available for routine use at NMRFAM are listed here.

Information on small molecule solution NMR applications is available here.

In the age of AlphaFold and Cryo-EM, NMR remains a vital tool for experimentally assessing the validity of protein structural models in solution, detect hydrogen bonding, and studying systems not amenable to crystallography or cryo-EM, such as membrane proteins lacking large soluble domains, fibrils lacking twist to aid alignment, small proteins in solution, and intrinsically disordered proteins or regions. NMR is highly complementary to other structural biology approaches and can add detailed information on the interactions of critical functional groups in active sites or provide experimental data for flexible regions that are poorly resolved in EM or crystallographic structures.

In studying molecular interactions, NMR is uniquely able to detect and characterize weak or transient interactions, including interactions between protein domains or between proteins and small molecules. NMR can directly detect protonation and deprotonation independent of any coupled effect on substrate binding or molecular structure, providing a valuable experimental tool for studying proton-coupled transport, proton-coupled enzymatic reactions, or pH-dependent allosteric regulation.

NMR is one of the most powerful methods to measure molecular motion because of the wide range of timescales that can be assessed and the information that can be simultaneously detected at multiple sites across a molecule. For slower process with a finite number of low energy states, NMR methods can simultaneously determine the relative populations and rates of exchange between states coupled with the chemical shift of the different states. This directly links thermodynamic, kinetic, and structural properties with site specific resolution that can immediately reveal whether a dynamic process is global or local.

Solution NMR studies of macromolecules (protein or RNA) are constrained by molecular size and the overall rotational correlation time of the molecule or complex. The flowchart below illustrates how molecular size impacts the choice to use solution or solid-state NMR approaches, the type of isotopic labeling needed for studies of macromolecular structure and dynamics, and the amount of material needed (usually a few milligrams per sample). NMRFAM staff can provide more specific guidance regarding your particular system.

Resonance assignment is the first step in most macromolecular NMR studies. This is the process by which specific nuclei in the molecule are correlated with each peak in the NMR spectrum. Once the resonances are assigned, they can be used to locate ligand binding sites and measure site-specific structural restraints or dynamics.

Macromolecular NMR user guide. NMRFAM capabilities are shown in red. Black are decision points based on user input. Intermediate decision point for SSNMR is shown in blue. Integration with cryo-EM is in green.