HNCOCA 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 ...
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 is transferred to the amide nitrogen, and then to the alpha carbon of the previous residue in the protein's amino acid sequence. In contrast, the complementary
HNCA experiment transfers magnetization to the alpha carbons of both the starting residue and the previous residue in the sequence. The HNCOCA experiment is used, often in tandem with HNCA, 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 specif ...
, 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 fou ...
.
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 only, while for the complementary
HNCA experiment peaks appear at and . 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 methods
Biophysics
Protein structure
Nuclear magnetic resonance experiments
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