Student Evening Series

Student Evening Series

April 14, 2021 @ 6:30 pm – 8:00 pm

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Examining the conformational dynamics of Na+/I symporter (NIS) using enhanced sampling methods 
Mayukh Chakrabarti (Amzel lab) 

The Na+/I symporter (NIS), a transmembrane protein found in the thyroid gland and other tissues, carries out the uptake of iodide, a required constituent of thyroid hormones T3 and T4. Physiologically, NIS transports iodide to the cytoplasm of thyroid cells with a stoichiometry of 2 Na+: 1 I, driven by the sodium concentration gradient maintained by the Na+/K+ ATPase. Our lab, together with Dr. Carrasco’s laboratory (Vanderbilt University), developed homology models of inwardly and outwardly open NIS, based on several recently determined structures of bacterial Na+-dependent transporters. The current view of NIS transport involves four principal states that can be characterized in a thermodynamic cycle: outwardly open with no ligands bound, outwardly open with all ligands bound, inwardly open with all ligands bound, and inwardly open with no ligands bound. However, the metastable intermediate states of NIS and their populations in these thermodynamic transitions have thus far not been elucidated. We employed molecular dynamics (MD) simulations, using an enhanced sampling technique, to characterize the transition of NIS between its inwardly and outwardly open states in the absence and presence of ions, and obtain insight into the populations and free energy differences of the states along this transition pathway. This information could be used to inform testable experimental assays for further validation.