17. - 18.08.2022 | NCCR TransCure Final Conference
University of Bern
Bühlstrasse 28, CH-3012
Go to the Conference website here.
Meet Andre Bazzone
Nanion Senior Scientist, Andre Bazzone will present a poster.
Presenter: Andre Bazzone
Title: Sugar binding and translocation in SGLT1: SSM-based electrophysiology reveals sugar occluded intermediates
Recently we described an electrophysiological assay revealing pre steady-state charge translocations in the human Na+/sugar cotransporter SGLT1 upon sugar binding. We postulated this correlates with local conformational transitions that transfer charged protein residues across the membrane. In general, this may be attributed to mechanisms such as induced fit, substrate occlusion, alternating access or the closure of the extracellular gate.
Here we applied SSM-based electrophysiology for a detailed functional characterization of SGLT1 revealing kinetic properties of sugar binding and translocation, including rate and 41 equilibrium constants, apparent KM values and relative Imax values for different sugar species. Based on the data we conclude a kinetic model describing the sugar translocation pathway in SGLT1, revealing new insights into the transport mechanism: (1) Sugar is able to bind to the outward facing, empty carrier. Hence, substrate binding may happen in random order, under high sugar and low sodium conditions. (2) Not sodium binding, but sugar binding leads to an electrogenic conformational transition within SGLT1 under 0 mV conditions, likely representing sugar occlusion with k+=60 s-1 and k-=200 s-1. (3) Following sugar occlusion, the rate limiting step in sugar translocation is the transition into the inward open conformation. It occurs at the slowest rate for D-glucose, but at higher rates for sugars with lower apparent affinities. (4) At 0 mV and saturating sugar concentrations, all reactions within the sugar translocation pathway are fast compared to the empty carrier translocation. After suger release, sodium release limits the slow transition of the empty carrier from the inward to the outward open state. A 10-state kinetic model has been established to describe the sugar translocation pathway involving three substrate induced electrogenic transitions. Further work is required to merge this model with existing models based on the knowledge about voltage driven transitions observed with conventional electrophysiology.
About the NCCR TRANSCURE Final Conference
The National Centre of Competence in Research (NCCR) TransCure is an interdisciplinary research network of 15 research groups affiliated to the Universities of Bern, Zurich, Lausanne and Basel. The main focus of this network is membrane transporter and ion channel research.
The NCCR TransCure is one of the current NCCRs funded by the Swiss National Science Foundation (SNSF). NCCRs goal is to promote research projects in areas of vital strategic importance that benefit Swiss economy, society and public health.