# Revisiting vSGLT: Non-Radioactive Characterization of the Vibrio Na+/Galactose Cotransporter by SURFE2R N1 Solid-Supported Membrane Electrophysiology

## TL;DR

This study uses a modern non-radioactive method to confirm the function of a bacterial sugar transporter, showing it works as previously thought.

## Contribution

The study introduces a non-radioactive method for characterizing vSGLT using electrophysiology.

## Key findings

- vSGLT shows Na+-dependent transport with D-galactose as the most effective substrate.
- The SURFE2R N1 system accurately measures vSGLT kinetics without radioactive labels.
- Km values for Na+ and galactose align with earlier radiolabeled studies.

## Abstract

The sodium–galactose cotransporter from Vibrio parahaemolyticus (vSGLT) was first cloned and functionally characterized by the laboratory of Ernest M. Wright in 2000, establishing a one-to-one Na+:sugar coupling stoichiometry and pioneering a bacterial model for human SGLTs. Here, we revisit vSGLT using solid-supported membrane electrophysiology on the Nanion SURFE2R N1, providing a modern, non-radioactive kinetic analysis of Na+-coupled sugar transport. Rapid transient currents were observed upon substrate application to proteoliposomes containing purified vSGLT. D-galactose elicited the largest Na+-dependent responses, followed by D-glucose and D-fucose, while no transport was observed in K+-based solutions. Apparent kinetic parameters recapitulate the overall trends observed in the original radiolabeled uptake assays, with Km(Na+) ≈ 18 mM and Km(gal) ≈ 9.8 mM. These findings validate the SURFE2R N1 SSM system as a quantitative, label-free method for Na+ symport characterization and demonstrate that vSGLT retains its canonical substrate selectivity and stoichiometry.