An important step towards highly effective drugs
Membrane receptors coordinate communications between cells – whether between single-celled organisms or the cells of a complex organism such as the human body. The huge receptor proteins traverse the cell membrane from the exterior surface to the inside. When a messenger molecule – or a pharmaceutical - successfully binds at the external surface, the protein conformation changes. This, in turn, activates a signal chain inside the cell. As potential drug targets, receptor proteins are highly in demand for testing the efficacy of new pharmaceuticals. Of special interest are the G protein-coupled receptors (GPCRs) because a wide range of diseases can be successfully treated with GPCR-targeting drugs.
But there are two major challenges: First, receptor proteins are very fragile and normally need to be embedded in a membrane. Second, drug candidates are typically much smaller than their potential receptors. Therefore it is nearly impossible to test the binding directly by conventional methods which depend on measuring changes in mass or size. Alternatives, such as indirect cell culture experiments, take much more time and consume more material.
The researchers from Boston and Munich combined two innovative techniques to overcome these barriers. The MIT group specializes in putting G protein-coupled receptors (GPCRs) into membrane-like structures made from artificial peptides. In this way the artificially produced receptors remain correctly folded and soluble.
The biophysicists of LMU used microscale temperature gradients to detect drug binding. This method is based on the fact that molecules - as for example the receptors - in solution move along a temperature gradient in a characteristic way. The scientists established a microscopic temperature gradient by localized laser heating of a test tube containing about 1 microliter sample solution. They compared the movement of the pure receptor with the molecule’s behavior after addition of a test drug. If the drug binds to the receptor molecule, the characteristics of its movement change. Not only is the setup of the so-called microscale thermophoresis (MST) binding assay very robust. The method is so sensitive that small, binding-induced changes in the conformation or shape of a GPCR can be detected using very small amounts of protein and test sample. By varying the amount of drug, the efficacy of the binding can be determined quantitatively.
These results document the successful combination of soluble GPC receptors with the microscale thermophoresis (MST) recently developed by the NanoTemper startup company. The new approach has great potential to become a simple and rapid standard assay for pharmaceutical and basic research (NIM).
"Peptide surfactants for cell-free production of functional G protein-coupled receptors".
Xiaoqiang Wang, Karolina Corin, Philipp Baaske, Christoph J. Wienken, Moran Jerabek-Willemsen, Stefan Duhr, Dieter Braun, Shuguang Zhang.
Proceedings of the National Academy of Sciences of America (PNAS), Published online May 9, 2011.
Prof. Dieter Braun
Systems Biophysics, Ludwig-Maximilians-Universität München
Phone: +49 (0) 89-2180-2317
Dr. Philipp Baaske
NanoTemper Technologies GmbH
Phone: +49 (0) 89-2180 2833