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Introduction to Solid Supported Membrane Based Electrophysiology

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Published on: May 11, 2013

Proton-coupled dynamics in lactose permease.

Magnus Andersson¹, Ana-Nicoleta Bondar, J Alfredo Freites

¹Department of Physiology and Biophysics and Center for Biomembrane Systems, University of California at Irvine, Irvine, CA 92697-4560, USA.

Structure (London, England : 1993)

|September 25, 2012

Summary

Molecular dynamics simulations reveal how lactose permease (LacY) transitions between inward and outward facing states. Deprotonation of a key residue, Glu325, triggers structural changes essential for H+ and sugar transport.

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Area of Science:

Biochemistry
Structural Biology
Computational Biology

Background:

Lactose permease (LacY) in Escherichia coli facilitates the transport of lactose and protons across the cell membrane.
This transport occurs through an alternating access mechanism, involving conformational changes between inward- and outward-facing states.
Understanding these conformational dynamics is crucial for elucidating LacY's transport mechanism.

Purpose of the Study:

To investigate the early dynamics of the inward-to-outward conformational transition of lactose permease (LacY).
To explore the role of Glu325 protonation state and lipid environment in LacY's conformational changes using molecular dynamics simulations.

Main Methods:

Molecular dynamics (MD) simulations were performed on wild-type apo LacY.
Simulations were conducted in phosphatidylethanolamine (POPE) lipid bilayers with two protonation states of Glu325.
Additionally, simulations were performed in dipalmitoylphosphatidylcholine (DMPC) lipids to assess lipid dependence.

Main Results:

Deprotonation of Glu325 induced significant structural rearrangements in LacY.
These rearrangements brought critical side chains for proton and sugar binding into proximity and closed the internal cavity.
The dynamics of LacY were found to be dependent on the surrounding lipid environment (POPE vs. DMPC).

Conclusions:

The simulations provide atomic-level insights into the early stages of the LacY inward-to-outward transition.
Glu325 deprotonation is a key event driving the conformational change and preparing LacY for substrate release and proton translocation.
The findings align with experimental observations and highlight the importance of lipid-protein interactions in transporter function.