Structur and pharmacology of GABAA receptors

Gamma-aminobutyric acid (GABA) is the major inhibitory transmitter of the central nervous system. Most of the actions of GABA are mediated by GABA A receptors. GABA A receptors are chloride ion channels formed from five protein subunits that can be opened by GABA and are the site of action of a variety of pharmacologically and clinically important drugs, such as benzodiazepines, barbiturates, neuroactive steroids, anesthetics and convulsants. For most of these compounds their site of interaction with GABA A receptors is not known. In this project we generated structural models of the extracellular and transmembrane domain of GABA A receptors using the structure of related receptors as a template. These models for the first time indicated that within the GABA A receptors there are at least 15 different solvent accessible pockets that probably are needed for conformational changes, but also might function as possible drug binding sites, explaining the complex pharmacology of these receptors. The models now can be used to visualize the pockets, to identify possible drug binding sites and to guide their further investigation. In one attempt to do so we used "in silico" docking studies to define how the anxiolytic, anticonvulsant, muscle relaxant, and sedative-hypnotic benzodiazepines bind into the benzodiazepine binding site of these receptors. Data obtained not only provided new information but also helped to improve our models of the receptors. In a different approach we more closely investigated another one of the 15 pockets. We succeeded not only to identify a novel drug binding site within this pocket, but also to identify a compound class able to interact with this site. Compounds from this structural class have the potential to exert a receptor subtype-selective action and can be used as lead compounds for the development of drugs with a novel mechanism of action that might be of clinical importance. Finally, within this project we developed a method for the mass expression and purification of GABA A receptors that can be used for the investigation of the structure and pharmacology of GABA A receptors using NMR and crystallization studies. These and similar studies will provide important structural information on the receptor and will form the basis for a future structure based drug design that will speed up the development of clinically important drugs.