Liapakis Lab
Department of Pharmacology, Faculty of Medicine
University of Crete
Many physiological functions in our body are mediated by the interaction of a large number of chemically divergent endogenous ligands, such as biogenic amines, peptides, glycoproteins, lipids and nucleotides, with the G-protein-coupled receptors (GPCRs). Furthermore, the sensation of exogenous stimuli, such as light, odors, and taste, is mediated via this class of receptors. The G-protein-coupled receptors (GPCRs) comprise the largest superfamily of proteins in the body and, playing a fundamental role in cellular function, are estimated to be the target for more than 50% of the currently available drugs.
These plasma membrane proteins share a common structural motif of seven membrane-spanning domains (TMs) (heptahelical motif), connected with three extracellular (EL) and three intracellular (IL) loops. Agonist binding to extracellular loops of GPCRs and/or to amino acids of the membrane-spanning domains located towards the extracellular portion of receptors promotes conformational changes that are propagated through their membrane-spanning domains to the intracellular portion of receptors. Such conformational alterations in the cytoplasmic portion of GPCRs promote their interaction with and subsequent activation of heterotrimeric G-proteins. Activated G-proteins modulate several cellular signaling pathways, thus resulting in a cellular response.
Despite the fact that all GPCRs share a common heptahelical motif and the common feature to interact with and activate G-proteins, they are remarkably diverse at the sequence level and fall into six families. The family A include the receptors related to the ''light receptor'' rhodopsin, dopamine and adrenergic receptors, whereas the family B include the receptors related to secretin, and corticotropin releasing factor (CRF) receptors (family B).
The long-term goal of our laboratory is to obtain information for the structure of GPCRs, to determine the mode of ligand binding to these receptors and to uncover the molecular mechanisms involved in their activation. These studies will put the basis for the design of receptor-selective ligands with predetermined efficacy. In specific, our laboratory engages in two specific areas of research:
