Conformational flexibility driving charge-selective substrate translocation across a bacterial transporter

Area of Science:

• Biochemistry and Biophysics
• Membrane Transport
• Molecular Biology

Background:

• Bacterial membrane porins control molecule passage, but the mechanism for large molecules is unclear.
• Understanding selective transport is crucial for developing new drug delivery strategies.

Purpose of the Study:

• To elucidate the molecular mechanism of selective large cyclic sugar uptake by the CymA transporter.
• To investigate the role of electrostatic interactions and conformational dynamics in CymA transport.

Main Methods:

• Utilized electrical recordings to measure transport kinetics.
• Employed protein mutagenesis to identify key structural elements.
• Performed molecular dynamics simulations to visualize transport pathways and energetics.

Main Results:

• Established that CymA transport is governed by pore electrostatics and a flexible N-terminal constriction segment.
• Demonstrated pH-dependent, reversible modulation of substrate binding and charge-selective transport.
• Molecular dynamics simulations confirmed experimental findings, revealing transport pathways and binding sites.

Conclusions:

• The CymA transporter's flexible constriction segment regulates energy-independent transport of large cyclic sugars.
• This mechanism differs from typical ligand-gated transport and offers potential for targeted drug design.