A structural Role for Serotonin Transporter Terminal Domains in Uptake Regulation

Abstract

Serotonin transporter (SERT) is a member of the Na+/Cl--dependent neurotransmitter transporter family (NSS or SLC6), which also includes norepinephrine transporter (NET) and dopamine transporter (DAT). SERT mediates rapid removal and recycling of released serotonin following neuronal stimulation. The activity of SERT is tightly regulated, as its misfunction is associated with diseases such as autism, bipolar disorder, depression, obsessive-compulsive disorder, migraine and anxiety. Regulation is modulated by post-translational modifications, including phosphorylation, glycosylation as well as by interaction with other proteins. The majority of this regulatory behavior involves the N- and/or C-terminal domains of the protein, the structure of which is not known. In order to determine the structural determinants of the SERT regulation we have generated a model of full-length SERT using a combination of template-based and de Novo modeling methodologies. The modeling process was carried out in three stages: a) modeling of the transmembrane segment of SERT using the X-ray structure of the bacterial homolog LeuT, b) modeling of both N- and C-terminal domains of the protein using a de Novo folding approach (Rosetta) and c) modeling of the full complex. The last two steps required extensive conformational sampling to ensure that native-like states were modeled. The best models were selected out using clustering and energetic criteria. We present a comparison of the models to the available experimental data.