Biophysical studies with G-protein-coupled receptors (GPCRs) are typically very challenging due to the poor stability of these receptors when solubilized from the cell membrane into detergent solutions. However, the stability of a GPCR can be greatly improved by introducing a number of point mutations into the protein sequence to give a stabilized receptor or StaR®. Here, we present the utility of StaRs for biophysical studies and the screening of fragment libraries. Two case studies are used to illustrate the methods: first, the screening of a library of fragments by surface plasmon resonance against the adenosine A(2A) receptor StaR, demonstrating how very small and weakly active xanthine fragments can be detected binding to the protein on chips; second, the screening and detection of fragment hits of a larger fragment library in an NMR format called TINS (target-immobilized NMR screening) against the β(1) adrenergic StaR.
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