A multi-enzyme machine polymerizes the Haemophilus influenzae type b capsule
Javier O. Cifuente, Julia Schulze, Andrea Bethe, Valerio Di Domenico, Christa Litschko, Insa Budde, Lukas Eidenberger, Hauke Thiesler, Isabel Ramón Roth, Monika Berger, Heike Claus, Cecilia D’Angelo, Alberto Marina, Rita Gerardy‐Schahn, Mario Schubert, Marcelo E. Guerin, Timm Fiebig
Abstract
Bacterial capsules have critical roles in host-pathogen interactions. They provide a protective envelope against host recognition, leading to immune evasion and bacterial survival. Here we define the capsule biosynthesis pathway of Haemophilus influenzae serotype b (Hib), a Gram-negative bacterium that causes severe infections in infants and children. Reconstitution of this pathway enabled the fermentation-free production of Hib vaccine antigens starting from widely available precursors and detailed characterization of the enzymatic machinery. The X-ray crystal structure of the capsule polymerase Bcs3 reveals a multi-enzyme machine adopting a basket-like shape that creates a protected environment for the synthesis of the complex Hib polymer. This architecture is commonly exploited for surface glycan synthesis by both Gram-negative and Gram-positive pathogens. Supported by biochemical studies and comprehensive 2D nuclear magnetic resonance, our data explain how the ribofuranosyltransferase CriT, the phosphatase CrpP, the ribitol-phosphate transferase CroT and a polymer-binding domain function as a unique multi-enzyme assembly.