Poster Presentation The 43rd Lorne Conference on Protein Structure and Function 2018

NMR based determination of ligand binding conformations at α1-Adrenergic receptor subtypes (#242)

Tasneem Vaid 1 2 3 , Kelvin Yong 1 2 3 , Daniel James Scott 1 3 , Paul Gooley 1 2
  1. Department of Biochemistry and Molecular Biology, The University of Melbourne, Melbourne, Victoria, Australia
  2. Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, Melbourne, Victoria, Australia
  3. The Florey Institute of Neuroscience and Mental Health , Melbourne, Victoria, Australia

Adrenergic receptor (AR) subtypes are G-Protein Coupled Receptors (GPCRs) activated by the same endogenous catecholamines, adrenaline and nor-adrenaline. The two subtypes α1A- and α1B-AR maintain a complex balance in modulating the functions of sympathetic and central nervous systems, whereby chronic activity can be either detrimental or protective for both heart and brain function. Regulation is believed to be mediated through the distinct activation of individual α1-AR subtypes and thus, subtype selective activation/blocking may have clinical implications for conditions such as heart failure, epilepsy and neurodegenerative diseases. Despite such physiological and pharmacological importance, there are no approved α1A- or α1B-AR selective marketed drugs. The reasons being there is limited structural information on GPCRs generally and specifically for these receptors, as well as conservation of the orthosteric binding site within the sub-family makes it difficult to achieve sub-type selectivity. Here we have used thermostabilized mutants of α1A- and α1B-AR to assess the binding conformation of two ligands: noradrenaline (a native agonist) and A61603 (α1A-AR selective agonist) by employing rapid atomic resolution, ligand-observed NMR methods including Saturation Transfer Difference NMR (STD-NMR), Tr-NOESY (Transferred Nuclear Overhauser Effect Spectroscopy) and INPHARMA (Interligand Noes for PHARmacophore Mapping). STD-NMR experiments are commonly used to detect weak ligand binding and for fragment screening. Tr-NOESY and INPHARMA, on the other hand take advantage of the Nuclear Overhauser Effect to detect and map ligand binding modes. The experimental results are further supported by homology modelling and docking procedures. Overall, the results illustrate this approach can determine the ligand binding conformation on GPCRs, which is a crucial step in a subtype selective drug development process.