Start-up Profiles

Published online: 23 June 2003, doi:10.1038/bioent751

m-phasys

Optimizing membrane protein expression.

The importance of membrane proteins in drug discovery is widely appreciated. Not only do they perform basic cell functions, such as the regulation of cell signaling through surface receptors (e.g., G-protein coupled receptors, or GPCRs), cell–cell interactions (integrins and adhesion proteins) and transport of molecules across the cell membrane, but they also account for almost 70% of all known pharmaceutical drug targets. Until recently, however, membrane proteins have been difficult to study, mainly because of their insolubility and relative scarcity compared with soluble proteins (See m-phasys profile).

Structure of the visual pigment rhodopsin.

To meet this need, German startup m-phasys has developed a technology for large-scale production of purified membrane proteins. Essentially, recombinant membrane proteins are expressed in E. coli inclusion bodies and refolded to become fully functional. This novel method can produce membrane proteins with a yield 100- to 10,000-fold higher than conventional methods.

In addition, proteins produced using the technology can easily be purified by means of affinity tags and do not require post-translational modification, such as glycosylation, phosphorylation and palmitoylation, to be functional (in contrast to receptors derived from tissue). According to the company, the protein preparation technology has been successfully applied to both GPCRs and ion channels.

One major project involves the determination of atomic-resolution structures of GPCRs, one of the major challenges in protein crystallography. Experimental structures of GPCRs would greatly enhance success rates in structure-based drug design and optimization, but progress has been limited by the difficulty of purifying and crystallizing the protein. The only GPCR whose three-dimensional structure has been determined thus far is the naturally abundant visual pigment rhodopsin.

Another project is the development of assays that rapidly and accurately assess the drug potential of biologically active chemical compounds targeting membrane proteins. The low abundance of these proteins in most eukaryotic expression systems limits large-scale screening with purified proteins, whereas assays based on whole cells are difficult to handle in terms of assay setup, storage and readout (because of false-positive hits due to endogenous GPCRs, toxicity effects, and other problems). The m-phasys technology produces membrane proteins in a purified and functional state, which can be used to develop new assay formats, especially those involving miniaturization to 384-well microplates or microchips. The success of m-phasys in refolding the first ion channel has led to a collaborative project with FlyIon (Tübingen, Germany) to develop an ion-channel screening assay.

The company is also collaborating with Medarex (Princeton, NJ, USA), Graffinity Pharmaceutical Design (Heidelberg, Germany) and Cosmix (Braunschweig, Germany) to build what it calls 'a lead-compound generation network.' In addition, the company has signed drug discovery deals with GlaxoSmithKline (Brentford, UK) and Bayer (Leverkusen, Germany) to develop tools for the structural analysis of membrane proteins and for membrane protein assay development.

MF