The last few years have seen a dramatic increase in the number of high resolution structures of integral membrane proteins being deposited in the Protein Data Bank. Despite these notable successes, producing large quantities of stable membrane protein suitable for structural studies is still far from a routine exercise. The challenge of large-scale expression and isolation of a wide range of membrane proteins was therefore taken up by the EDICT consortium; seven of the manuscripts in this edition describe the different approaches taken.
Bettaney et al. describe the use of Escherichia coli expression systems for the production of bacterial inositol transporters and their assessment of suitable candidates for further study. Öberg and Hedfalk review the use of the yeast Pichia pastoris for the successful production of human aquaporins, while Leung et al. describe the modifications required to produce a stable form of the fungal nucleobase ascorbate transporter, UapA. Krenc et al. describe how the heterologous expression of some ammonia-conducting aquaporins changes the behaviour of Saccharomyces cerevisiae cells. Expression in mammalian hosts has yet to obtain widespread acceptance as a means of producing membrane proteins for structural studies, but in his review Tate argues that this is a highly suitable system, which is not as expensive as one might think. Kellosalo et al. describe the methods that they used to isolate and crystallize membrane-bound pyrophosphatases and introduce us to a novel detergent that may have significant potential as an alternative crystallization agent. Finally, cell-free expression approaches and their use for membrane proteins have been pioneered by the group of Frank Bernhard and in their review they provide a detailed overview of this method.
EDICT partners also focused on how structure in combination with mutagenesis approaches can be used to better understand the mechanisms of action of a variety of membrane proteins. This is exemplified by a review on the conformational changes in NhaA by Kozachkov and Padan. Finally, Conner et al. review sub-cellular translocation as a regulatory mechanism of aquaporin function.
In the next issue of this special edition, further articles on structure-activity relationships are presented together with others on drug screening/ligand binding demonstrating how structural information can be translated into platforms for discovery of novel drugs.
Roslyn Bill and Bernadette Byrne
Professor Roslyn M. Bill, School of Life & Health Sciences, Aston University; [email protected] and Dr Bernadette Byrne, Division of Molecular Biosciences, Imperial College London; [email protected]