Solid state NMR for studying membrane proteins
Solid state NMR is now established as a method for resolving structural information for large biomolecular complexes such as membrane-embedded proteins. In principle, there is no molecular weight limit to the use of the approach, although the complexity and volume of data is still outside complete assignment and structural determinations for any large (Mr > ∼40k) complex, unless specific methods are used to reduce the information content. Such methods include specific residue type labelling, labelling of putative segments of a protein, probing ligand binding sites with labelled ligands, or examination of complexes made up of smaller, manageable units, such as oligomeric ion channels. Labelling possibilities often follow models from a bioinformatics approach. In all cases, and in common with most membrane studies, sample preparation is vital, and this activity alone can take considerable effort before NMR can be applied-peptide or protein production (synthesis or expression) followed by reconstitution into bilayers and/or chemical synthesis, and then resolution of suitable sample geometry, is still technically challenging. As experience is gained in the field, this development time should decrease. Here, a brief overview of the use of solid state NMR for membrane protein structural determinations will be presented. © 2007 Springer Science+Business Media B.V.