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Disentangling Glycan-Protein Interactions: Nuclear Magnetic Resonance (NMR) to the Rescue
Published on: May 17, 2024
Sugar binding and protein conformational changes in lactose permease
Ying Yin1, Morten Ø Jensen, Emad Tajkhorshid
1Theoretical and Computational Biophysics Group, Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, IL, USA.
Biophysical Journal
|September 12, 2006
Summary
Molecular dynamics simulations reveal that glutamate 269 (Glu269) is crucial for lactose permease function. Its protonation state controls lactose import by altering protein conformation and ion interactions.
Area of Science:
- Structural biology
- Biophysics
- Molecular dynamics simulations
Background:
- Lactose permease facilitates lactose import across cell membranes using a proton gradient.
- Previous studies suggested transport intermediates but lacked mechanistic understanding of protonation and conformational changes.
- The precise role of key residues in coupling proton translocation and substrate transport remained unclear.
Purpose of the Study:
- To elucidate the molecular mechanism of lactose/H(+) co-transport by lactose permease.
- To investigate the role of residue protonation states in protein conformational changes during transport.
- To understand the coupling between proton translocation and lactose binding/unbinding.
Main Methods:
- Molecular-dynamics simulations of membrane-embedded lactose permease.
- Simulations were performed in various protonation states, with and without lactose.
- Analysis focused on pore diameter, salt-bridge formation, and substrate motion.
Main Results:
- Glutamate 269 (Glu269) is identified as a primary proton translocation site, controlling transport steps via its protonation state.
- Protonation of Glu269 breaks the Glu269-Arg144 salt bridge, leading to conformational changes and cytoplasmic half-channel closure.
- Charged Glu269 strongly binds lactose, indicating protonation is necessary for substrate release.
Conclusions:
- The protonation state of Glu269 is central to lactose permease transport mechanism.
- A novel mechanism for cytoplasmic entrance gating involving Glu269 and Arg144 is proposed.
- Understanding these dynamics provides insights into secondary active transport mechanisms.
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