02.12.2021 - Structure and Function of Na+ and H+ dependent transporters

Session Abstract: 

Na/H exchangers are a important and diverse family of secondary active transporters. These proteins are crucial in pH, sodium and volume homeostasis, dysfunction is critical in eukaryotes and procaryotes alike. In the final session of the Transporter Webinar Series David Drew and Matthias Quick share some of their research on the structure and function of this transporter family.  

Speakers: 

Title: Structure and mechanism of the Na⁺/H⁺ exchanger NHA2

David Drew, Professor in Biochemistry,
(Stockholm University)

Abstract: 

SLC9B2, also known as NHA2, correlates with the long-sought after sodium/lithium (Na+/Li+) exchanger linked to the pathogenesis of diabetes mellitus and essential hypertension in humans. Despite its functional importance, structural information and the molecular basis of its ion-exchange mechanism have been lacking. Here, we I briefly present the cryo EM structures of bison NHA2 in detergent and in nanodiscs at 3.0 and 3.5 Å resolution, respectively. I will then show how SSM-based electrophysiology has enabled us to conclude that NHA2 catalyses the electroneutral rather than electrogenic exchange of ions. The ion-binding site is quite distinctive, with a tryptophan-arginine-glutamate triad separated from the well-established ion-binding aspartates. These triad residues fine-tune ion binding specificity, as demonstrated by a salt-bridge swap mutant that converts NHA2 into a Li+-specific transporter.

Title: The molecular mechanism of the Na⁺/H⁺ antiporter NhaA – from binding to flux

Dr. Matthias Quick, Associate Professor of Neurobiology,
Departments of Psychiatry and Physiology and Cellular Biophysics,
Columbia University Irving Medical Center

Abstract: 

The Na+/H+ antiporter NhaA represents the archetype of Na+/H+ exchangers, evolutionarily conserved proteins in all kingdoms of life that are essential in cellular ion homeostasis. While structural information has provided excellent starting points in developing mechanistic models of NhaA-mediated transport, the correlation between the correlation of Na+ and H+ binding and flux remains still enigmatic. Since structural information about the composition of the Na+ and H+ sites in NhaA is missing, functional assays are required to gain insight into the molecular events that regulate NhaA activity. By using the SURFE2R N1 SSM platform, our team was able to collect data of NhaA-mediated ion flux across the membrane of NhaA-containing proteoliposomes. Direct Na+ binding studies in conjunction with flux studies reveal that, whereas Na+ transport is impaired at low pH, NhaA can bind Na+ in pH-independent fashion, providing new insight into the interplay of the two cations during transport.

When: Thursday December 2nd, 4 PM CET, 10 AM EST

Watch On-Demand Here

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