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Lipopolysaccharide binding to the periplasmic protein LptA
Kathryn M Schultz1, Tanner J Lundquist1, Candice S Klug1
1Department of Biophysics, Medical College of Wisconsin, Milwaukee, Wisconsin, 53226.
Protein Science : a Publication of the Protein Society
|April 19, 2017
Summary
This study quantifies how lipopolysaccharide (LPS) binds to the periplasmic protein LptA in Gram-negative bacteria. Findings reveal a 1:1 complex, altered protein structure upon binding, and a 1:1 LPS:LptA ratio.
Area of Science:
- Bacterial outer membrane biogenesis
- Protein-lipid interactions
- Molecular mechanisms of transport
Background:
- Lipopolysaccharide (LPS) is crucial for Gram-negative bacteria outer membrane structure and defense.
- LptA facilitates LPS transport across the periplasm to the outer membrane.
- Understanding LPS-LptA interaction is key to bacterial cell envelope biogenesis.
Purpose of the Study:
- To comprehensively characterize and quantify the binding interaction between LPS and LptA.
- To identify the specific binding site of LPS within LptA.
- To determine the stoichiometry and affinity of the LPS-LptA complex.
Main Methods:
- Site-directed spin-labeling electron paramagnetic resonance (EPR) spectroscopy.
- Collection of EPR data for 15 spin-labeled residues in LptA.
- Analysis of mobility changes and binding location upon addition of exogenous LPS.
Main Results:
- EPR data indicate a 1:1 stoichiometry for the LPS:LptA complex.
- Dissociation constants for the LptA-LPS interaction were calculated for the first time.
- LPS binding affects the entire LptA protein, causing N-terminus unfolding.
- A mutant LptA unable to form oligomers showed altered LPS binding affinity.
Conclusions:
- The study provides the first quantitative characterization of LPS binding by LptA.
- LPS binding induces significant conformational changes in LptA.
- Oligomerization may play a role in LptA's affinity for LPS.