Investigating the structure of tetraspanin membrane proteins

Tetraspanin membrane proteins are emerging as potential therapeutic targets for major human disorders such as cancer, infection and inflammatory diseases. Tetraspanins function by regulating other membrane proteins including certain proteases, ion channels and adhesion proteins. The tetraspanins are important for the trafficking of these partner proteins to the cell surface and for their lateral mobility and clustering on the cell surface. There are 33 tetraspanins in humans but many remain functionally uncharacterised. Nevertheless, experiments in tetraspanin knockout mice and cultured cells, and genome-wide association studies, are revealing tetraspanin links to human disease. Moreover, recent structural studies show that tetraspanins have cone-shaped structures with the potential for conformational change and drug targeting. The overarching aim of this project is to discover novel mechanisms of tetraspanin action using our recently developed lipid nanodisc technology, namely styrene maleic acid lipid particles (SMALPs). SMALPs are 10 nm diameter particles containing discs of the plasma membrane and a surrounding belt of styrene maleic acid (SMA) copolymer. The SMA effectively acts as a ‘cookie cutter’ when applied to cultured cells, in generating discs of membrane proteins encapsulated within the lipid bilayer. Importantly, membrane protein complexes are retained within SMALPs, enabling their functional and structural characterisation in their native lipid environment. Our analyses of SMALPs on native protein gels using a novel methodology, SMA-polyacrylamide gel electrophoresis (PAGE), has revealed new tetraspanin interacting partners.

The objectives of the project are as follows:

● To identify novel tetraspanin interaction partners using SMA-PAGE and mass spectrometry proteomics.

● To investigate how tetraspanins regulate the identified partners using CRISPR/Cas9 knockout of the tetraspanins and functional assays in cultured cells.

● To gain structural information on tetraspanin complexes with partner proteins in SMALPs. The impact of the project will be the identification of novel mechanisms by which tetraspanins regulate cell function, thus enabling future translational work on tetraspanins as drug targets in human disease.