HNCA is a 3D NMR

NMR

NMR may refer to:Applications of Nuclear Magnetic Resonance:* Nuclear magnetic resonance* NMR spectroscopy* Solid-state nuclear magnetic resonance* Protein nuclear magnetic resonance spectroscopy* Proton NMR* Carbon-13 NMR...

 experiment commonly used in the field of protein NMR

Protein nuclear magnetic resonance spectroscopy

Nuclear magnetic resonance spectroscopy of proteins is a field of structural biology in which NMR spectroscopy is used to obtain information about the structure and dynamics of proteins. The field was pioneered by Richard R. Ernst and Kurt Wüthrich, among others...

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

Amino acid

Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...

 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 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

Carbon-13

Carbon-13 is a natural, stable isotope of carbon and one of the environmental isotopes. It makes up about 1.1% of all natural carbon on Earth.- Detection by mass spectrometry :...

 and ¹⁵N isotopic labelling

Isotopic labeling

Isotopic labeling is a technique for tracking the passage of a sample of substance through a system. The substance is 'labeled' by including unusual isotopes in its chemical composition...

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

Recombinant DNA

Recombinant DNA molecules are DNA sequences that result from the use of laboratory methods to bring together genetic material from multiple sources, creating sequences that would not otherwise be found in biological organisms...

.

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 {H_N(i), N(i), C_alpha (i)} and {H_N(i), N(i), C_alpha(i-1)}, while for the complementary HNCOCA experiment peaks appear only at {H_N(i), N(i), C_alpha(i-1)}. 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.

Citations

General references

Protein NMR Spectroscopy : Principles and Practice (1995) John Cavanagh, Wayne J. Fairbrother, Arthur G. Palmer III, Nicholas J. Skelton, Academic Press