Blood group antigen recognition by a solute-binding protein from a serotype 3 strain of Streptococcus pneumoniae

Area of Science:

• Microbiology
• Biochemistry
• Structural Biology

Background:

• Streptococcus pneumoniae causes significant human diseases like pneumonia.
• Bacterial virulence is linked to carbohydrate metabolism, but S. pneumoniae's glycan targets are not fully understood.
• A known fucose utilization operon contributes to virulence in some S. pneumoniae strains.

Purpose of the Study:

• To identify and characterize novel carbohydrate utilization pathways in S. pneumoniae.
• To investigate the role of fucose metabolism in S. pneumoniae virulence.
• To understand the molecular basis of S. pneumoniae's interaction with host glycans.

Main Methods:

• Genomic analysis to identify new operons.
• Protein expression and purification.
• Isothermal titration calorimetry to assess binding affinity.
• X-ray crystallography to determine protein-sugar complex structure.

Main Results:

• A second fucose utilization operon was identified in a subset of S. pneumoniae strains, including serotype 3.
• The operon encodes a fucose solute-binding protein (FcsSBP) that specifically binds A and B blood group trisaccharides.
• Structural analysis revealed FcsSBP binds to the reducing end of these trisaccharides, indicating a requirement for soluble blood group antigens.

Conclusions:

• Certain S. pneumoniae strains possess an uncharacterized system for transporting host histo-blood group antigens.
• This finding reveals a new mechanism for S. pneumoniae to acquire nutrients and potentially enhance virulence.
• The study highlights the importance of host glycan structures in bacterial pathogenesis.