PhD Exit Seminar – Raphaël Brisset Di Roberto

PhD Exit Seminar

Tuesday August 29^th, 1:10 pm – Ramsay Wright Building, Room 432

Raphaël Brisset Di Roberto (Peisajovich/ Chang lab)

“Evolutionary alternatives on the road to a new specificity in a G protein-coupled receptor”

Abstract

Cells sense change in their external environment and react appropriately through the action of signaling pathways. This process is initiated by receptor proteins with a high degree of specificity for a particular stimulus. G protein-coupled receptors form the largest family of membrane protein receptors and their ability to sense a broad variety of ligands is unparalleled despite their common ancestral origin. How GPCRs evolved their unique specificities is unknown, although ligand binding affinity is often given a central role. The goal of this thesis was to assess the possible contributions of secondary mechanisms of specificity, namely ligand efficacy and downstream signaling regulation, to changes in ligand recognition. Through directed evolution, we generated a yeast pheromone receptor with an altered specificity in two steps. First, promiscuous receptors were obtained through either improved binding affinity or weaker molecular interaction with a negative regulator of signaling. Second, a ligand-discriminating receptor was obtained from a promiscuous variant solely by reducing the efficacy of the native pheromone. These findings demonstrate the importance of assessing GPCRs’ pharmacological profiles in their native context, where signaling trumps binding affinity in significance.