Molecular Modelling Of ATP-Gated P2X Receptor Ion Channels

P2X receptors (P2XRs) are trimeric cation channels activated by extracellular ATP. Human P2XRs (P2X1-7) are expressed in nearly all mammalian tissues, and they are an important drug target because of their involvement in inflammation and neuropathic pain. The aim of this thesis is to address the following questions. P2XR crystal structures have revealed an unusual U-shape conformation for bound ATP; how does the U-shape conformation of ATP and its derivatives affect channel activation? Where and how do the selective, non-competitive inhibitors AZ10606120 and A438079 bind to P2X7R? What is the structure of the hP2X1R intracellular domain in the closed state? Molecular modelling and bioinformatics were used to answer these questions, hypotheses resulting from this work were tested in collaboration with Prof. Evans. Investigating the binding modes of ATP and its deoxy forms in hP2X1R showed that the ribose 2′-hydroxyl group is stabilising the U-shape conformation by a hydrogen bond to the γ-phosphate. The reduced ability of 2′-deoxy ATP to adopt the U-shape conformation could explain its weak agonist action in contrast to full agonists ATP and 3′-deoxy ATP. Ligand docking of AZ10606120 and A438079 into the hP2X7R predicted an allosteric binding site, this site has meanwhile been confirmed by P2X7R/antagonist X-ray structures. MD simulations suggested that unique P2X7R regions (residues 73-79 and T90/T94) contribute to an increase of the allosteric pocket volume compared to the hP2X1R. This difference in size might be the key for selectivity. The hP2X1R intracellular domain in the closed state was modelled ab initio, and interpreted in context of chemical cross-links (collaboration with Prof. Evans). This suggests a symmetrical arrangement of two short b-antiparallel strands within the Nterminal region and short a-helix in the C-terminal region and additional asymmetrical states.