Magnetic susceptibility

The state of the art in spectrometry - an ultra-highfield wide-bore NMR machine - will soon allow scientists to take a close look at thousands of membrane proteins with unprecedented resolution

By | October 6, 2000

LONDON. The state of the art in spectrometry has arrived at Leiden University where researchers inaugurated an ultra-highfield wide-bore NMR machine this week. The prototype machine has been installed and tested over the last year and will soon allow scientists to take a close look at thousands of membrane proteins with unprecedented resolution.

"This is a major step forward, because it gives an improvement in range, resolution and sensitivity, opening up new and unexplored fields of membrane protein research," enthuses NMR team leader Huub de Groot. The Bruker-built machine operates at a radio field frequency of 750 MHz. This represents a twofold increase on conventional biological solid state NMR, which is normally performed at 300-400 MHz and as such represents a potential 60% increase in sensitivity. The machine uses a highly stable and powerful (17.6 T) wide-bore superconducting magnet meaning large samples and even living organisms can be studied.

Magic Angle Spinning (MAS) underpins the machine's power. Samples are held at 54.5 degrees to the main field and spun at three million RPM so the NMR signals are narrowed making them more distinct. "This allows investigations of membrane proteins in the membrane's natural environment," explains de Groot. Colleague Suzanne Kiihne adds that techniques such as signal addition mean they can improve sensitivity still further. "It has already been possible to assign nearly all the carbon, nitrogen, and proton signals from a 63 residue protein in the solid state," she says. "This amounts to separating over 350 signals from a solid sample."

One of the primary jobs for the NMR machine will be to look at the molecular structure of membrane proteins of which there are some 50,000 in the human body involved in our senses, thought processes, allergies and countless other processes. Relatively little is known about membrane proteins because instrumentation and methods with which to handle them have not been powerful enough. The pharmaceutical industry, however, potentially has thousands of membrane receptor targets awaiting analysis so access to detailed information could open the floodgates to novel therapies for a wide range of diseases from depression to arthritis.

Solid state NMR is the only method that can obtain suitable structural information for intact membrane complexes. "We will begin to move from description to genuine understanding, from the deductive biological approach to the inductive approach of the physical sciences," says de Groot. He even suggests a move towards descriptions down to the level of the Schroedinger equation for parts of membrane proteins and their ligands. This will allow a more predictive view than the traditional descriptive approaches. "The first examples have been realised, but this may take a while…" he concedes.

Researchers are already queuing up to use the machine with an international workshop running October 4-8. "The benefits are twofold," explains de Groot, "scientists can take snapshots of drugs and hormones bound to their receptor targets, and second, carry out functional magnetic resonance imaging, of small animals, to elucidate the role of genes in the development of organs." The wider bore allows more electronics and larger samples to be used points out Kiihne.

"With this instrument, we can do imaging experiments on mice and spinning experiments on samples of 25 microlitres or indeed at slower spin speeds on up to a gram," she adds.

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