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Spectrum Descriptions
This page contains a list of some solid-state magic-angle spinning (MAS) NMR experiments which are useful for protein solid-state MAS NMR assignment and structure calculations. For each experiment there is short description and an illustration showing the
observed magnetisation transfers. The
exact pathway is not described, as in many cases several pathways are possible, or the exact mechanism of magentisation transfer may not be known. In general, the atoms which are observed are shown in pink and those atoms through which magnetisation flows are shown in light blue (though there may be more than just these involved!). Magnetisation transfers which are usually only observed when longer mixing times are used, are shown in grey. An example spectrum or diagramatic spectrum shows what it should look like and particular features and considerations are highlighted. The descriptions here are very simplistic and for a full description, including pulse sequences, the reader should consult the original articles.
PDSD - Proton Driven Spin Diffusion (2D)
Reference:
N. Bloembergen (1949)
Physica 15 386-426. (
Link to Article)
min. labelling: 13C
Magnetization is transferred from hydrogen to 13C nuclei. From here it is transferred to other 13C nuclei which are close in space. As the name of the experiment suggests, protons are involved in this transfer (though this is not specifically indicated in the diagram).
This is the most standard experiment and could be considered the solid-state euqivalent of the HSQC. It is probably the first experiment you will record on a protein sample and should help you assess the genereal quality of the spectra you can achieve with that sample. Essentially all 13C atoms within a certain distance of one another are correlated by cross peaks in the spectrum. In practice this means that at short mixing times all carbon atoms within one spin-system (residue) are coupled to one another (except perhaps for some longer-range pairs of atoms such as Cα and Cε). At longer mixing times correlations between residues will appear, too.
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DARR - Dipolar Assisted Rotational Resonance (2D)
References:
K. Takegoshi, S. Nakamura and T. Terao (2001)
Chem. Phys. Lett. 344 631-637. (
Link to Article)
K. Takegoshi, S. Nakamura and T. Terao (2003)
J. Chem. Phys. 118 2325-2341. (
Link to Article)
min. labelling: 13C
Magnetization is transferred from hydrogen to 13C nuclei. From here it is transferred to other 13C nuclei which are close in space.
This experiment is similar to the PDSD, but at long mixing times the transfer of magnetisation is more efficient and so you can expect to see more cross peaks.This experiment is useful in order to obtain inter-residue contacts for assignment and structure calculations.
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NCA (2D)
Reference:
M. Baldus, A.T. Petkova, J. Herzfeld and R.G. Griffin (1998)
Mol. Phys. 95 1197-1207. (
Link to Article)
min. labelling: 15N, 13C
Magnetisation is transferred from 1H to 15N via cross polarisation and then selectively to the 13Cα using specific cross polarisation. The chemical shift is evolved on the 15N nuclei and detected on the 13C nuclei.
This experiment can be used in the early stages of a project to assess the nitrogen line widths. It may also provide a means for assigning the nitrogen chemical shifts.
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NCO (2D)
Reference:
M. Baldus, A.T. Petkova, J. Herzfeld and R.G. Griffin (1998)
Mol. Phys. 95 1197-1207. (
Link to Article)
min. labelling: 15N, 13C
Magnetisation is transferred from 1H to 15N via cross polarisation and then selectively to the 13CO using specific cross polarisation. The chemical shift is evolved on the 15N nuclei and detected on the 13C nuclei.
This experiment can be used to obtain sequential links from Ni to COi-1 but for larger proteins, this is liable to be rather crowded and the 3D NCOCX experiment will probably be more useful.
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NCACX (2D or 3D)
Reference:
J. Pauli, M. Baldus, B.-J. van Rossum, H. de Groot and H. Oschkinat (2001)
Chem. Biochem. 2 272-281. (
Link to Article)
min. labelling: 15N, 13C
Magnetisation is transferred from 1H to 15N via cross polarisation and then selectively to the 13Cα using specific cross polarisation. A
PDSD or
DARR step is then used to transfer magnetisation to any other 13C nuclei nearby. The chemical shift is evolved on the 15N and 13Cα nuclei and then detected on 13C, resulting in a 3D spectrum. A 2D version in which the 13Cα evolution time is left out is also possible.
When recorded with short mixing times for the CX step (10-50ms) this experiment is very useful for the identification of spin systems, i.e. all 13C and 15N resonances belonging to a single residue. When using longer mixing times (200-500ms) it is possible to see links to other carbon atoms nearby and restraints for structure calculations can be obtained, or links to neighbouring amino acids can help with assignment.
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NCOCX (2D or 3D)
Reference:
J. Pauli, M. Baldus, B.-J. van Rossum, H. de Groot and H. Oschkinat (2001)
Chem. Biochem. 2 272-281. (
Link to Article)
min. labelling: 15N, 13C
Magnetisation is transferred from 1H to 15N via cross polarisation and then selectively to the 13CO using specific cross polarisation. A
PDSD or
DARR step is then used to transfer magnetisation to any other 13C nuclei nearby. The chemical shift is evolved on the 15N and 13CO nuclei and then detected on 13C, resulting in a 3D spectrum. A 2D version in which the 13CO evolution time is left out is also possible.
This spectrum is very useful during assignment. At short mixing times for the CX step (10-50ms) it links Ni to COi-1 and other carbon atoms from residue i. This provides unambiguously sequential links between residues. When using longer mixing times (200-500ms) it is possible to see links to other carbon atoms nearby and restraints for structure calculations can be obtained.
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NCACB (2D or 3D)
Reference:
J. Pauli, M. Baldus, B.-J. van Rossum, H. de Groot and H. Oschkinat (2001)
Chem. Biochem. 2 272-281. (
Link to Article)
min. labelling: 15N, 13C
Magnetisation is transferred from 1H to 15N via cross polarisation and then selectively to the 13Cα using specific cross polarisation. A
DREAM step is then used to transfer magnetisation to 13Cβ nuclei further along the amino acid side chain. The chemical shift is evolved on the 15N and 13Cα nuclei and then detected on 13C, resulting in a 3D spectrum. A 2D version in which the 13Cα evolution time is left out is also possible.
This spectrum is very useful for identifying amino acid spin systems and to some extent 'decrowding' the NCACX spectrum. The DREAM transfer is optimised for transfer from Cα to Cβ, but some Cγ will also become excited and be visible in the spectrum, because their chemical shifts are similar to some Cβ chemical shifts. Because the DREAM transfer is a double quantum step, the Cβ peaks will be negative and the Cγ peaks will be positive.
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CANCO (2D or 3D)
References:
Y. Li, D.A. Berthold, H.L. Frericks, R.B. Gennis, C.M. Rienstra (2007)
Chem. Biochem. 8 434-442. (
Link to Article)
min. labelling: 15N, 13C
Magnetisation is transferred from 1H to 13Cα via cross polarisation and then selectively to the 15N using specific cross polarisation. A further specific cross polarisation step is used to transfer the magnetisation onto 13CO nuclei.The chemical shift is evolved on the 13Cα nuclei and 15N nuclei and then detected on the 13CO nuclei, resulting in a 3D spectrum. A 2D version of this experiment is also possible, in which the 15N evolution time is omitted.
This experiment is a useful addition to the NCACX and NCOCX during assignment, providing useful quasi-through-bond links between two sequential residues (i.e. Cαi-Ni-COi-1). The main problem with this experiment is its low signal-to-noise. The three CP transfers tend to have fairly low transfer efficiency. On a sample which suffers from low signal-to-noise anyway, there may not be enough signal left to detect at the end of this experiment.
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CANCOCX (4D)
Reference:
W.T. Franks, K.D. Kloepper, B.J. Wylie and C.M. Rienstra (2007)
J. Biomol. NMR 39 107-131. (
Link to Article)
Magnetisation is transferred from 1H to 13Cα via cross polarisation and then selectively to the 15N using specific cross polarisation. A further specific cross polarisation step is used to transfer the magnetisation onto 13CO nuclei. Finally a PDSD step is used to transfer the magnetisation to any other 13C nuclei nearby. The chemical shift is evolved on the 13Cα, 15N and 13CO nuclei and then detected on 13C. Lower dimensionalities are also possible by eliminating one or both of the 15N and 13CO evolution periods. min. labelling: 15N, 13C
This experiment is extremely useful for assignment, providing useful quasi-through-bond links between two sequential residues with a further, e.g. Cαi-Ni-COi-1-Cαi-1 and decreasing overlap problems on account of its being a 4D experiment. As with the CANCO, the main problem with this experiment is its low signal-to-noise. The three CP transfers tend to have fairly low transfer efficiency. On a sample which suffers from low signal-to-noise anyway, there may not be enough signal left to detect anything at the end of this experiment. However, if you do get this to work, then a small protein can be assigned very easily using this experiment (see
Franks et al. 2007).
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CHHC (2D)
Reference:
A. Lange, S. Luca and M. Baldus (2002)
J. Am. Chem. Soc. 124 9704-9705. (
Link to Article)
min. labelling: 15N, 13C
Magnetisation is transferred from 1H to 13C via cross polarisation. In three successive steps it is first transferred back to 1H, then to other 1H nuclei nearby, and finally back to 13C for detection. The chemical shift is evolved on the 13C nuclei following the initial cross polarisation and detected on the 13C nuclei at the end, resulting in a 2D carbon-carbon spectrum, but which encodes information about proton-proton distances of the protons attached to the carbon atoms.
This experiment is particularly useful for obtaining proton-proton structural restraints which can be used in protein structure calculations.
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NHHC (2D)
Reference:
A. Lange, S. Luca and M. Baldus (2002)
J. Am. Chem. Soc. 124 9704-9705. (
Link to Article)
min. labelling: 15N, 13C
Magnetisation is transferred from 1H to 15N via cross polarisation. In three sucessive steps it is first transferred back to 1H, then to other 1H nuclei nearby, and finally onto 13C for detection. The chemical shift is evolved on the 15N nuclei following the initial cross polarisation and detected on the 13C nuclei at the end, resulting in a 2D carbon-nitorgen spectrum, but which encodes information about proton-proton distances of the protons attached to the carbon and nitrogen atoms.
This experiment is particularly useful for obtaining proton-proton structural restraints which can be used in protein structure calculations.
