HNCA is a 3D triple-resonance

NMR Nuclear magnetic resonance (NMR) is a physical phenomenon in which nuclei in a strong constant magnetic field are perturbed by a weak oscillating magnetic field (in the near field) and respond by producing an electromagnetic signal with a ...

experiment commonly used in the field of

protein NMR Nuclear magnetic resonance spectroscopy of proteins (usually abbreviated protein NMR) is a field of structural biology in which NMR spectroscopy is used to obtain information about the structure and dynamics of proteins, and also nucleic acids, and ...

. The name derives from the experiment's magnetization transfer pathway: The magnetization of the amide proton of an

amino acid residue Protein structure is the molecular geometry, three-dimensional arrangement of atoms in an amino acid-chain molecule. Proteins are polymers specifically polypeptides formed from sequences of amino acids, the monomers of the polymer. A single ami ...

is transferred to the amide nitrogen, and then to the alpha carbons of both the starting residue and the previous residue in the protein's amino acid sequence. In contrast, the complementary

HNCOCA HNCOCA is a 3D triple-resonance NMR experiment commonly used in the field of protein NMR. The name derives from the experiment's magnetization transfer pathway: The magnetization of the amide proton of an amino acid residue is transferred to the ...

experiment transfers magnetization only to the alpha carbon of the previous residue. The HNCA experiment is used, often in tandem with HNCOCA, to assign alpha carbon resonance signals to specific residues in the protein. This experiment requires a purified sample of protein prepared with ¹³C and ¹⁵N

isotopic labelling Isotopic labeling (or isotopic labelling) is a technique used to track the passage of an isotope (an atom with a detectable variation in neutron count) through a reaction, metabolic pathway, or cell. The reactant is 'labeled' by replacing specific ...

, at a concentration greater than 0.1 mM, and is thus generally only applied to

recombinant proteins Recombinant DNA (rDNA) molecules are DNA molecules formed by laboratory methods of genetic recombination (such as molecular cloning) that bring together genetic material from multiple sources, creating sequences that would not otherwise be foun ...

. The spectrum produced by this experiment has 3 dimensions: A proton axis, a ¹⁵N axis and a ¹³C axis. For residue i peaks will appear at and , while for the complementary

experiment peaks appear only at . Together, these two experiments reveal the alpha carbon chemical shift for each amino acid residue in a protein, and provide information linking adjacent residues in the protein's sequence.

References

Citations

General references

Protein NMR Spectroscopy : Principles and Practice (1995) John Cavanagh, Wayne J. Fairbrother, Arthur G. Palmer III, Nicholas J. Skelton, Academic Press Protein methods Biophysics Protein structure Nuclear magnetic resonance experiments {{protein-stub