Analyzing the Signature of GPCR Conformational Changes

G protein coupled receptors (GPCRs) are integral membrane proteins that allow a cell to convert extracellular stimuli like light, small molecules, peptides, and proteins into intracellular signals. These receptors are conformationally very malleable, which is necessary for their different functional states. Recent developments in the structural biology of membrane proteins and the utilization of other biophysical techniques for GPCRs are generating rich evidence of the existence of multiple receptor conformations. The structures are being generated in the inactive, active, and intermediate states for many GPCRs, however, there is no unbiased way to characterize the functional states of GPCRs. We are developing general higher-order GPCR topology parameters (TMHTOP2) that can find functional-state specific structural signatures and can be applied to any alpha-helical transmembrane protein. The newly developed TMHTOP2 topology parameters were able to identify unique conformational signatures of the pre-active state of the A2A receptor compared to its inactive and active states, that can now be used to identify the pre-active states of other receptors as well. This method can be used in identifying and classifying structures from experiments or simulations as active, inactive, and intermediates.