Prof. Dr. Peter Gmeiner
Friedrich-Alexander-University of Erlangen-Nuremberg
Department Chemie und Pharmazie

Prof. Dr. Brian Kobilka
Stanford University
Kobilka Lab

Catecholamine receptors including a number of adrenergic and dopaminergic subtypes are known as target proteins for CNS- and cardiovascular-active drugs and serve as model systems for understanding the structure, cell biology, and physiology of GPCR-ligand complexes. Brian Koblika’s lab at Stanford has developed direct methods to monitor ligand-induced conformational changes β₂ adrenergic receptors. Peter Gmeiner’s group in Erlangen has substantial experience in the design and organic synthesis of novel, highly specific GPCR agonists and antagonists. Employing the β₂ subtype as a model system for a class A rhodopsin-like GPCR, the collaboration between the Bavarian and the Californian research group will focus on chemical synthesis of tailor-made GPCR ligands and their biological investigation as molecular probes to gain novel insights into the protein recognition and activation processes.

Final report:

Supported by the funding of BaCaTeC, my laboratory initiated a scientific collaboration with Prof. Brian Kobilka and his research group at Stanford University. After initial discussions in 2006, we started a common research program. Our activity began immediately after Brian Kobilka’s lab was able to publish the first X-ray crystal structure of the ß₂-adrenoreceptor, a G-protein coupled receptor, in its inactive state. In this case, the membrane protein was stabilized by an inverse agonist. The aim of our collaboration was to get access to the first agonist-bound G-protein coupled receptor.

Because it was known that the binding affinity of agonists in the binary complex between a G-protein coupled receptor and its ligand is low (low affinity state), we decided to develop a strategy that allowed us to substantially reduce the dissociation rate of the ligand bound to the receptor. The result of our discussion was to develop a covalently binding ß₂-adrenoceptor agonist that was able to more or less irreversibly associate with a receptor, so that the dissociation was set formally to zero. We identified a position in the receptor (position 93 in transmembrane helix 2) that could be mutated to cysteine without affecting the functionality of the receptor. Based on the crystal structure of the inactive state, we estimated the distance between this position and the pharmacophore of the agonist to be designed. Upon combination of the structure of different heterocyclic bioisosteres of norepinephrine with linker sequences of different length and a functionality that was expected to covalently bind to the mutated cysteine in transmembrane helix 2, our investigations resulted in an evolutionary process leading to the covalent ß₂-adronoceptor agonist FAUC 50. In fact, the compound showed covalent binding to the receptor and the functional properties of a full agonist. After careful functional studies, crystallization experiments in the laboratory of Brian Kobilka at Stanford University led to a crystal structure of the first agonist-bound GPCR. The work was published in Nature in 2011.

Subsequently, the Kobilka lab could also resolve a crystal structure of a ternary complex with a G-protein mimetic nanobody and with the trimeric G-protein. 2012, Brian Kobilka received the Nobel Prize for his structural characterizations of G-protein coupled receptors.

Meanwhile, we intensified our collaboration resulting in three more common articles published in Nature, PNAS and Molecular Pharmacology. Thanks to the initiation by BaCaTeC, our collaboration is now funded by the National Institutes of Health providing my laboratory with grant money for further scientific investigations in the field of medicinal chemistry of G-protein coupled receptors. The aim of this NIH project is to develop allosteric ligands based on newly developed GPCR crystal structures.