Solution NMR studies of membrane-protein-chaperone complexes

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• Bacterial outer membrane biogenesis requires molecular chaperones to prevent hydrophobic membrane protein aggregation during periplasmic transport.
• Understanding these chaperone-protein interactions is crucial for deciphering bacterial cell envelope assembly.

Purpose of the Study:

• To investigate the structural and functional aspects of periplasmic membrane-protein-chaperone complexes using NMR spectroscopy.
• To characterize the binding of Escherichia coli outer membrane protein OmpX to chaperones Skp and SurA.
• To assess the refolding competence of OmpX when bound to Skp and identify key interaction sites.

Main Methods:

• High-resolution Nuclear Magnetic Resonance (NMR) spectroscopy in aqueous solution.
• Analysis of membrane-protein-chaperone complex structures and functions.
• Amino acid mutation analysis to probe protein-chaperone interactions.

Main Results:

• Escherichia coli outer membrane protein OmpX binds to both Skp and SurA chaperones in structurally similar states, despite chaperone structural differences.
• The Skp-bound state of OmpX is functionally equivalent to a chemically denatured state regarding refolding into detergent micelles.
• Amino acid mutation analysis indicates that the two most hydrophobic segments of OmpX do not solely drive its interaction with Skp.

Conclusions:

• Molecular chaperones Skp and SurA bind OmpX in conserved structural states, facilitating its periplasmic transport.
• Skp binding to OmpX primes it for membrane insertion by maintaining a partially unfolded state.
• OmpX-Skp interaction involves more than just the protein's most hydrophobic regions, suggesting complex binding determinants.