Definitive structural assessment of enterococcal diheteroglycan

Area of Science:

• Microbiology and Immunology
• Carbohydrate Chemistry
• Structural Biology

Background:

• Enterococcus faecalis is a significant cause of difficult-to-treat, multi-antibiotic resistant nosocomial infections.
• The cell-wall polysaccharide diheteroglycan (DHG) from E. faecalis has shown promise as a vaccine candidate.
• The stereochemical configuration of the lactic acid (LA) residue on DHG's galactofuranoside unit is critical for its biological function but was previously unassessed.

Purpose of the Study:

• To determine the configuration of the lactic acid (LA) residue attached to the galactofuranoside unit of Enterococcus faecalis diheteroglycan (DHG).
• To investigate how this configuration impacts DHG's conformation, biological recognition, and immune evasion properties.
• To provide foundational knowledge for the development of a synthetic E. faecalis vaccine.

Main Methods:

• Chemical analysis of the DHG structure.
• Nuclear Magnetic Resonance (NMR) spectroscopy, specifically investigating intramolecular Nuclear Overhauser Effects (NOE).
• Molecular dynamics simulations of native DHG and synthetic R and S models derived via pyranoside-into-furanoside rearrangement.

Main Results:

• The study definitively proves the R configuration of the lactic acid (LA) residue in the native E. faecalis DHG.
• Analysis of NMR NOE data and molecular dynamics simulations supported the R configuration and provided insights into conformational differences.
• Synthetic R and S models were generated to facilitate comparative analysis and structural elucidation.

Conclusions:

• The R configuration of the LA residue in E. faecalis DHG has been established.
• This stereochemical determination is essential for understanding DHG's role in host-pathogen interactions and immune response.
• The findings pave the way for the rational design and synthesis of an effective E. faecalis vaccine to combat resistant infections.