NMR

Instrumentation

The NMR laboratory holds a 950 MHz spectrometer (installation summer 2013), which is the highest field NMR magnet in Northern Europe. In addition the NMR laboratory include seven high-field spectrometers operating at 700, 600, 500, 400 (two), 300, and 200 MHz (1H resonance frequencies). 

700 MHz: The actively shielded 700 MHz wide bore spectrometer is used for diverse range of applications. It is equipped with 4 mm and 2.5 mm broadband triple resonance MAS probes, a 2.5mm 1H-19F-X probe, a 4 mm 1H-31P-13C HR-MAS probe, a 5 mm TXI liquid state probe, a triple resonance flat coil probe for oriented sample studies, and two probes for high field micro imaging. 


500 MHz: The 500 MHz (also actively shielded) standard bore spectrometer comes with a sample jet facilitating high throughput of samples making it ideal for e.g. metabolomics-related project and the like. The spectrometer is – for now – equipped with a 5 mm TXI liquid state probe and a 4 mm triple resonance (1H-13C-15N) probe for solid state NMR experiments.

400 MHz: The 400 MHz spectrometer is a wide bore instrument and it is used for both solid-state and liquid-state NMR experiments. The instrumentation include both 4 mm and 2.5 mm broad band triple resonance MAS probes as well as commercial and home built flat coil probes used for oriented samples. Moreover, a standard 5 mm TXI liquid state probe is available.

400 MHz
500 MHz
700 MHz

Computers: In the development of new methods and software, the NMR laboratory uses a local computer cluster (‘NMR cluster’) including 16 Linux-based computers with 4 processors each. Besides we are users of a larger computer cluster (‘Grendel’) located at the Danish Center for Scientific Computing, Aarhus.     

Examples on research projects

3D structure of solid-state proteins and peptides

One of the main goals in inSPIN is to solve three-dimensional structures of insoluble proteins and peptides. Fibrils are a class of molecules which normally not go into solution, and are typical not crystallized, and the structure of fibrils therefore cannot be found using liquid-state NMR or X-ray crystallography. Instead solid-state NMR is an ideal tool, since fibrils normally show a high degree of local order, resulting in narrow NMR signals.
An example of a study of fibrils is the elucidation of the three dimensional structure of the NFGAIL stretch in the hIAPP(20-29) peptide from the human islet amyloid polypeptide , which is associated with type II diabetes. The fibril structure was calculated on the basis of symmetry considerations from the multiplicity of the NMR signals, and from structural constraints found in the spectra.

Left: The eight possible ‘zipper’ types with indications of the resulting signal multiplicity.
Right: The calculated three-dimensional structure of the NFGAIL peptide in fibrils of hIAPP(20-29).

For more details, see J.T. Nielsen et al, Angw. Chem. 48 (2009) 2118-2121. Similar studies are on-going with focus on fibrils associated with other amyloid diseases (Alzheimers, Parkinsons, etc).

Structure of photoreceptor

Green sulphur bacteria have the largest known antenna system in photosynthetic organisms, and this antenna system, the chlorosome, is a highly complex organelle built of e.g. lipids, pigments and proteins. A certain mutant of Chlorobaculum tepidum, a model organism for green sulphur bacteria, gives rise to a smaller chlorosome, called a carotenosome. These carotenosomes are still highly complex systems, but the amount of pigment is lowered and instead of around ten different proteins in the chlorosomes, the carotenosomes hold primarily one protein, CsmA, located in the chlorosome baseplate. The structure of CsmA in solution has been solved (see below) using liquid-state NMR.

20 calculated structures of CsmA in solution. See M.Ø. Pedersen et al, FEBS Lett. 582, (2008), 2869-2874.

Method development

Since solid-state NMR is chronically impaired by low sensitivity, we are constantly trying to improve the performance of existing experiments and to develop new pulse sequences with improved sensitivity and/or new spectral features. For example, we have focused a great deal on optimizing the 15N --> 13C magnetization transfer and two new achievements are shown below. To the left are shown 1D and 2D NCA (a) and NCO (b) spectra of U-13C,15N Ubiquitin acquired using novel pulse sequences numerically optimized using optimal control (OC) algorithms. The 1D OC spectra (black) are seen to compare favourably with conventional methods (grey). To the right, uniformly 13C,15N labelled GB1 protein (β1-domain of the immunoglobulin binding protein G) has been used as sample in a 2D 15N-13C correlation spectrum acquired with a pioneering broadband pulse sequence element built on exponentially modulated rf fields.

For more details see C. Kehlet et al, J. Magn. Reson. 188 (2007) 216-230 (left) and A.B. Nielsen et al, J. Phys. Chem. Lett. 1 (2010) 1952-1956.

Dynamics of oriented membrane proteins

We have devoted major emphasis on characterizing both the membrane bound conformation and conformational dynamics of antimicrobial peptides. By combined 15N and 2H studies of the peptaibol Alamethicin, we have characterized its conformational dynamics, which are significant for small membrane bound peptides.

Small peptides display significant dynamics in their membrane anchoring. From combined 15N and 2H analyses, we have found the movements of the center of mass of the two CB atoms of Aib8 of Alameticin to make significant excursions, as visualized above. (Bertelsen et al. JACS (2009))

Contact

For more information on equipment and experiments, please contact 
Morten Bjerring, ph.d
Email:  bjerring@chem.au.dk 
Phone: +45 8715 6654 or +45 6082 8180

NMR group, Oct 2009