Serotonin transporter import

Abstract

Neurotransmitter Sodium Symporters modulate neurotransmission and members of this family of transporters are a popular target in the treatment of depression, addiction, obsessive compulsive disorder, and generalized anxiety disorder including the serotonin transporter and the dopamine transporter. These transporters have been the targets of numerous mutagenesis studies, none so expansive as our deep mutational scans, where we have characterized the effects of every point mutant on the function and surface localization of two of these proteins, the serotonin transporter (SERT) and the dopamine transporter (DAT). Collaborating with Diwakar Shukla’s group at UIUC, we have further advanced the understanding of function in these transporters by performing molecular dynamics simulations with and without various substrates. These simulations support our deep mutagenesis conclusions, while yielding novel information about the binding characteristics of both the native and non-native substrates for the human serotonin transporter, a representative member of this symporter family. Work with SERT and DAT lead us to hypothesize that the conformational equilibria of the transport cycle in these transporters is affected differentially for substrate import by mutations which stabilize sampling one conformation over another. Using molecular dynamics, we have observed a third ion binding site previously unrecognized in this transporter. Further, we have effectively used deep mutational scanning in yeast to engineer increased receptor-ligand affinity utilizing the PDGF-B PDGFRß system.