Key diffusion mechanisms involved in regulating bidirectional water permeation across E. coli outer membrane lectin

Area of Science:

• Structural biology and biophysics
• Microbial pathogenesis

Background:

• Capsular polysaccharides (CPSs) are key bacterial virulence factors aiding immune evasion.
• Wzi protein in E. coli mediates the attachment of group 1 K30CPS to the bacterial surface.
• Phylogenetic analysis suggests Wzi belongs to the porin superfamily.

Purpose of the Study:

• To elucidate the structural and functional roles of Wzi, particularly its interaction with K30CPS.
• To investigate the potential dual function of Wzi beyond lectin activity.

Main Methods:

• Structure-based phylogenetic analysis of Wzi.
• Molecular dynamics (MD) simulations to study Wzi's pore and function.
• Analysis of periplasmic substitution mutants to assess Wzi's role in osmoregulation.

Main Results:

• MD simulations reveal Wzi functions as a bidirectional, water-specific porin, previously unrecognized due to an occluded pore.
• Five entry points regulate water diffusion, with a luminal hydrophobic plug controlling permeation.
• The 'YQF' triad in the sugar-binding site suggests a role in K30CPS anchorage, and Loop 5 (L5) is crucial for membrane insertion.

Conclusions:

• Wzi possesses a dual role: anchoring capsular polysaccharides and facilitating osmoregulation via water transport.
• Interfering with Wzi's water diffusion or Loop 5 insertion could potentially reduce bacterial virulence.
• Findings offer new insights into bacterial immune evasion mechanisms and potential therapeutic targets.