Membrane transporters and channels allow molecules and ions to cross cell membranes. Dysregulation of the proteins can lead to disease and inhibition of the proteins by pharmaceuticals can be exploited for drug discovery.
Research in our laboratory focusses on two main types of membrane proteins and we are offering projects based on either of these.
The first project area involves connexins, which are large pore channels that are regulated by various signals, such as pH, voltage or Ca2+. Ground-breaking research in Warwick has shown that connexin26 (Cx26) is also directly regulated by CO2 independently of pH (1), and this can affect the control of breathing (2). Mutations of
Cx26 are one of the main causes of congenital deafness, with rare mutations causing keratitis ichthyosis deafness syndrome (KIDS). Connexins function either as channels through a single membrane (a hemichannel) or as a channel between two neighbouring cells formed from two docked hemichannels (a gap junction). Interestingly whereas CO2 closes gap junctions it opens hemichannels (3). Using cryo-EM we have shown the effect that CO2 has on the structure of the gap junctions, modulating the aperture of the channel (4). However, we still do not understand this process fully or know how CO2 can have a different effect on the hemichannels. A PhD project for connexins could investigate these questions further, using cryo-EM to investigate how CO2 affects channels or hemichannels and how this is affected by different disease-causing
mutations. The project would be co-supervised by Prof Nicholas Dale who made the discovery of the direct effect of CO2 on the activity of the channels. There would also be scope to do biophysical studies and/or molecular dynamics on this topic.
The second project field involves structural studies of membrane transport proteins. A major area of our research has been investigating a particular family of secondary transport proteins: the solute carrier 10 family. The founding members of this family are the apical sodium dependent bile acid transporter (ASBT) and the Na+ taurocholate cotransporting polypeptide (NTCP), both of which transport bile acids. An inhibitor of ASBT has been approved as a drug against chronic constipation. NTCP, which is found in the liver, on the other hand is of great interest because it is the target for hepatitis B virus entry into the liver and inhibitors of NTCP are being developed as viral entry inhibitors. Though we have solved the structure of a bacterial homologue of ASBT (5)
and the structure of NTCP has just been reported, there is still relatively little information on how bile acids are transported across the membrane or how inhibitors prevent transport. A transporter-based project would involve structural studies of members of the SLC10 family to investigate the binding of small molecules. X-ray
crystallography will be coupled with biochemical and biophysical assays and molecular dynamics. There is, however, scope to investigate other membrane transport proteins using similar techniques eg (6).
The project would be co-supervised by Prof Phill Stansfeld, an expert in molecular dynamics.
References:
1. Meigh L, Hussain N, Mulkey DK, & Dale N (2014) Connexin26 hemichannels with a mutation that causes KID syndrome in humans lack sensitivity to CO2. Elife 3, e04249. doi:10.7554/eLife.04249
2. van de Wiel J, Meigh L, Bhandare A, Cook J, Nijjar S, Huckstepp R, & Dale N (2020) Connexin26 mediates CO2-dependent regulation of breathing via glial cells of the medulla oblongata. Commun Biol 3, 521. doi:10.1038/s42003-020-01248-x
3. Sarbjit Nijjar DM, Louise Meigh, Elizabeth de Wolf, Thomas Rodgers, Martin Cann, Nicholas Dale (2020) Opposing modulation of Cx26 gap junctions and hemichannels by CO2
4. Brotherton DH, Savva CG, Ragan TJ, Dale N, & Cameron AD (2022) Conformational changes and CO2-induced channel gating in connexin26. Structure. doi:10.1016/j.str.2022.02.010
5. Hu NJ, Iwata S, Cameron AD, & Drew D (2011) Crystal structure of a bacterial homologue of the bile acid sodium symporter ASBT. Nature 478, 408-411. doi:10.1038/nature10450
6. Hatton CE, Brotherton DH, Spencer M, & Cameron AD (2022) Structure of cytosine transport protein CodB provides insight into nucleobase-cation symporter 1 mechanism. EMBO J, e110527. doi:10.15252/embj.2021110527
BBSRC Strategic Research Priority: Understanding the rules of life – Structural Biology.
Techniques that will be undertaken during the project:
Molecular biology
Growth of bacterial cultures
Solubilisation and purification of membrane proteins
Protein crystallisation, X-ray data collection and structure solution
Cryo-EM, depending on the exact project.
Biochemical assays
Molecular Dynamics Simulations
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