Fold it: Solid-state NMR unravels proteins

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  • Published: Apr 1, 2012
  • Author: David Bradley
  • Channels: NMR Knowledge Base
thumbnail image: Fold it: Solid-state NMR unravels proteins

Solid approach to protein structure

SS NMR vs XRD.

Researchers have developed a novel solid-state NMR spectroscopic method that uses paramagnetic tags to help them visualize the shape of protein molecules. The technique could be used to help scientists understand the properties of various biological molecules under normal, healthy conditions and also in those that are involved in a range of diseases.

Solid state NMR spectroscopy has been around for more than a decade and is often used to complement X-ray crystallographic studies as well as provide insights into often intractable membrane proteins and other substances that cannot be crystallised. Despite major efforts over the years to translate solid state NMR data into actual three-dimensional protein structures that step has often remained difficult.

Now, Christopher Jaroniec of Ohio State University and his colleagues writing in the journal Nature Chemistry have described a new approach to solid state NMR that exploits paramagnetic tags to make 3D visualisation a lot more accessible.

"Structural information about biological molecules is critical to understanding their function," explains Jaroniec. "Our new method promises to be a valuable addition to the NMR toolbox for rapidly determining the structures of protein systems which defy analysis with other techniques."

Focal point

A common focus of structural studies are the protein systems known as amyloids. These fibrous clusters of proteins are present in various disease states in cells, perhaps most notably in neurological diseases in humans including Alzheimer's disease. Understanding the detailed structure of such substances and how is varies in healthy and unhealthy tissue is important for finding new avenues to follow towards therapeutic interventions.

"Although for the purposes of the paper we tested the method on a small model protein, the applications are actually quite general," Jaroniec explains. "We expect that the method will work on many larger and more challenging proteins."

To test their new approach to solid state NMR, the team chose a protein called GB1, this common protein is found in streptococcus bacteria rather than human tissues. It has been studied in detail previously by scientists, so the structure is familiar. The team, however, engineered a new form of the protein where they swapped out various amino acid residues and replaced them with cysteine to which a copper ion could be attached as a paramagnetic tag using the chelating agent ethylenediaminetetraacetic acid (EDTA). The tags thus provide structural cues as to the environment of the local folding of the protein allowing the team to calculate the folded shape of the GB1 protein knowing the positions of the copper ions in the protein sequence and based on the NMR data.

Jaroniec' worked with doctoral students Ishita Sengupta, Jonathan Helmus and Philippe Nadaud at Ohio State and Charles Schwieters of the National Institutes of Health with financial support from the National Institutes of Health itself and National Science Foundation.

Breaking bottlenecks

The new approach could smash the bottleneck in non-crystallographic structural studies of biological macromolecules by furnishing large numbers of greater than 5 Å distance restraints that are difficult to extract from standard measurements of dipole-dipole couplings between protein nuclei in such molecules using magic angle spinning NMR data, explains Jaroniec.

The technique was "sufficient to obtain a protein back-bone fold for GB1 that is in close agreement with the X-ray structure, without the requirement for any conventional internuclear distance restraints," the team says. The researchers concede that the 3D structure they obtained is not at as high a resolution as is possible with X-ray techniques, but given that the use of solid state NMR is often required when diffraction-quality crystals are unavailable, then this marks a significant step forward in this area. The resolution they obtained will be adequate for many applications. 

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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