How Membrane Defects Accelerate Outer Membrane β-Barrel Protein Folding

Transmembrane β-barrel proteins found in the outer membrane of bacteria, mitochondria, and chloroplasts are classified as Outer Membrane Protein (OMPs).  β-barrel OMPs are important because they transport small molecules and proteins, are involved in outer membrane maintenance and bacterial virulence, plus affect antibiotic resistance.
 
The general goal of the current research is to understand the factors involved in β-barrel OMP folding.   Previous work suggests phosphoethanolamine headgroups present in lipid monomers comprising the bilayer slow down or create a high kinetic barrier to bacterial OMP folding(1). This process allows the cell to control OMP folding1. The proposed model correlates with the proposed role of the β-barrel assembly machinery (BAM), which is essential for reducing the kinetic barrier required for proper folding of β-barrel OMP. 
 
In addition to headgroup composition, other physical properties of membranes influence the rate and efficiency of OMP folding: 
 
·         Bilayer curvature
·         Hydrophobic thickness
·         Acyl chain saturation

Technical Advances

The work of Karen Fleming and Emily Danoff at the T. C. Jenkins Department of Biophysics, Johns Hopkins University,  tests the theory that any defect in the above membrane properties would reduce the kinetics and allow OMPs to more easily fold and insert in the outer membrane. The net effect of defect-mediated acceleration of folding would be that the cell/organelle would partially lose control over its membrane protein machinery.
 
To assess this idea, the team tested the effect on folding caused by bilayer structural changes (defects) occurring during the phase transition. The results indicated that folding increased as the incidences of bilayer defects increased. 
 
For a more thorough review of the work, please review Membrane Defects Accelerate Outer Membrane β‑Barrel Protein Folding.

 

Anatrace Connection

As always,  Anatrace products are working behind the scenes. In the paper one of the critical lipids used in this work was DMPC. Anatrace products have been used in membrane protein research for over 25 years. Our products are unmatched in combining purity and batch-to-batch consistency.   

Reference:
  1. Danoff, E. J. and Fleming, K. G. (2015) Biochemistry 54(2), 97–99.

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