Making the Enterobacterial Common Antigen Glycan and Measuring Its Substrate Sequestration

Area of Science:

• Microbiology
• Biochemistry
• Glycobiology

Background:

• Enterobacterial common antigen (ECA) is a crucial polysaccharide in Enterobacteriaceae, influencing outer membrane permeability.
• ECA biosynthesis competes for shared substrates, notably polyisoprenoid phosphate (BP), a carrier for multiple essential glycans.
• Understanding substrate competition is vital for deciphering bacterial glycan synthesis regulation.

Purpose of the Study:

• To provide biochemical evidence for the impact of glycan pathway disruption on endogenous polyisoprenoid pools.
• To investigate the effect of ECA biosynthesis disruption on polyisoprenoid phosphate (BP) levels.
• To establish methods for assessing ECA glycan and understanding polysaccharide interdependence.

Main Methods:

• In vitro enzymatic synthesis of ECA repeat units and LC-MS characterization of standards.
• Cloning and expression of genes involved in ECA biosynthesis.
• Generation of ECA-deficient mutants and analysis of accumulated intermediates and BP levels via LC-MS.

Main Results:

• Successfully reconstituted the ECA biosynthesis pathway in vitro, generating characterized standards.
• ECA-deficient mutants accumulated intermediates indistinguishable from synthesized standards.
• A significant decrease in cellular BP levels was observed in ECA-deficient mutants, correlating with pathway disruption.

Conclusions:

• This study provides the first direct biochemical evidence for polyisoprenoid phosphate (BP) sequestration upon disruption of bacterial glycan biosynthesis pathways.
• Genetic disruption of ECA synthesis leads to the accumulation of specific glycan intermediates and depletion of BP.
• Reveals a dynamic interdependence within the bacterial polysaccharide repertoire, highlighting substrate competition as a regulatory mechanism.