Cell-Free Expression to Probe Co-Translational Insertion of an Alpha Helical Membrane Protein

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• Most alpha-helical membrane proteins fold during synthesis (co-translational folding).
• Traditional folding studies use refolding from denatured states, not mimicking natural processes.
• Cell-free translation offers a method to study folding as proteins are synthesized.

Purpose of the Study:

• To explore co-translational folding and membrane insertion of complex membrane proteins.
• To adapt cell-free translation for studying proteins with intricate topologies.
• To investigate the folding and insertion of the bacterial leucine transporter (LeuT).

Main Methods:

• Utilized *in vitro* transcription-translation systems for cell-free synthesis of LeuT.
• Investigated the impact of lipid composition on LeuT insertion.
• Assessed the role of bacterial translocons in LeuT membrane incorporation.

Main Results:

• LeuT synthesis and membrane insertion were achieved using cell-free systems.
• LeuT insertion efficiency showed minimal dependence on lipid composition or translocon presence.
• Compared to simpler transporters, LeuT exhibited less efficient cell-free insertion, suggesting aggregation due to complex topology formation.

Conclusions:

• Cell-free translation is a viable method for studying co-translational folding of complex membrane proteins.
• LeuT's knotted structure presents challenges during co-translational insertion into membranes.
• This approach provides insights into protein formation during synthesis and lipid insertion.