Charged residues render pro-OmpA potential dependent for initiation of membrane translocation

Area of Science:

• Bacterial protein translocation
• Membrane biophysics
• Protein folding and insertion

Background:

• Outer membrane protein A (OmpA) is crucial for bacterial outer membrane integrity.
• Protein translocation across the bacterial inner membrane is a complex, essential process.
• The role of charge and membrane potential in protein translocation is not fully understood.

Purpose of the Study:

• To investigate how charged residues in the OmpA precursor (pro-OmpA) affect its translocation across the bacterial inner membrane.
• To determine the influence of membrane potential on pro-OmpA translocation based on its charge.

Main Methods:

• Utilized a cell-free translocation system.
• Systematically altered charged residues in the pro-OmpA leader peptide.
• Measured pro-OmpA insertion and translocation rates under varying membrane potential conditions.

Main Results:

• Insertion of two positive charges after the leader peptide inhibited pro-OmpA translocation.
• Introduction of neutral or negative charges allowed pro-OmpA translocation.
• Membrane potential stimulated translocation of negatively charged pro-OmpA but inhibited positively charged pro-OmpA.

Conclusions:

• Acidic residues in pro-OmpA render its translocation potential-dependent.
• Charge-dependent loop formation is critical for initiating pro-OmpA translocation.
• Understanding these mechanisms can inform strategies for controlling bacterial protein transport.