A multi-enzyme machine polymerizes the Haemophilus influenzae type b capsule

Area of Science:

• Microbiology
• Structural Biology
• Biochemistry

Background:

• Bacterial capsules are crucial for immune evasion and survival during host infections.
• Haemophilus influenzae serotype b (Hib) causes severe pediatric infections, necessitating effective vaccines.

Purpose of the Study:

• To define the capsule biosynthesis pathway of Haemophilus influenzae serotype b (Hib).
• To characterize the enzymatic machinery involved in Hib capsule synthesis.
• To enable fermentation-free production of Hib vaccine antigens.

Main Methods:

• Reconstitution of the capsule biosynthesis pathway.
• X-ray crystallography to determine the structure of the capsule polymerase Bcs3.
• Biochemical studies and 2D nuclear magnetic resonance (NMR) for mechanistic insights.

Main Results:

• Detailed characterization of the Hib capsule biosynthesis pathway.
• The X-ray crystal structure of Bcs3 revealed a multi-enzyme machine with a basket-like shape.
• Elucidation of the roles of CriT, CrpP, and CroT within the enzyme assembly.

Conclusions:

• The defined pathway and enzyme structures facilitate the production of Hib vaccine antigens.
• The basket-like architecture of Bcs3 protects the complex polymer synthesis.
• Understanding this pathway offers insights into surface glycan synthesis in various pathogens.