Wzx flippases exhibiting complex O-unit preferences require a new model for Wzx-substrate interactions

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• The Wzx flippase is essential for O-antigen biosynthesis in Gram-negative bacteria.
• Wzx facilitates the transport of O-antigen units across the inner membrane.
• Understanding Wzx substrate specificity is crucial for comprehending O-antigen assembly.

Purpose of the Study:

• To investigate the substrate specificity of Yersinia pseudotuberculosis Wzx flippases.
• To determine how structural variations in O-antigen units affect Wzx translocation.
• To propose a new model for Wzx-mediated substrate recognition.

Main Methods:

• Identification and characterization of Yersinia pseudotuberculosis Wzx proteins.
• Analysis of Wzx translocation efficiency with various O-antigen structures.
• Development of the "Structure-Specific Triggering" model.

Main Results:

• Two Yersinia pseudotuberculosis Wzx variants distinguished between different terminal dideoxyhexose sugars.
• Some Wzx variants efficiently translocated structurally divergent foreign O-antigen units.
• Wzx substrate preference is more complex than previously assumed, with specific residues being key determinants.

Conclusions:

• Wzx flippase substrate specificity is intricate and not solely dependent on the entire O-unit structure.
• A "Structure-Specific Triggering" model explains how Wzx achieves high-frequency translocation of preferred substrates.
• This finding advances our understanding of bacterial cell wall biosynthesis and Wzx function.