Proposed dual membrane contact with full-length Osh4

Area of Science:

• Cell Biology
• Biophysics
• Computational Biology

Background:

• Membrane contact sites (MCSs) are crucial for organelle structure and lipid transport.
• Yeast oxysterol binding protein (Osh4) is implicated in lipid trafficking but its behavior at MCSs is not fully understood.

Purpose of the Study:

• To elucidate the structure and dynamics of Osh4 at MCSs using computational methods.
• To investigate Osh4's interaction with dual membranes, particularly those with anionic lipids.

Main Methods:

• All-atom molecular dynamics (AA MD) simulations over microsecond timescales.
• Enhanced sampling techniques and targeted molecular dynamics simulations.
• CHARMM36m forcefield with CUFIX parameters for lipid-protein interactions.

Main Results:

• Osh4 was observed in a stable dual-membrane bound state at MCSs.
• The protein interacts with one membrane via its β-crease and the other via the α6-α7 region.
• Binding energy calculations identified the phenylalanine loop and α6 helix as key stabilizing elements.
• Computational findings align with experimental cross-linking data.

Conclusions:

• Osh4 can adopt a unique dual-membrane bound conformation at MCSs.
• This conformation is critical for Osh4's function in lipid transfer.
• The study provides atomic-level insights into protein-membrane interactions at MCSs.