Bacterial polysaccharide co-polymerases share a common framework for control of polymer length

Copyright © 2008 Nature Publishing GroupThe chain length distribution of complex polysaccharides present on the bacterial surface is determined by polysaccharide co-polymerases (PCPs) anchored in the inner membrane. We report crystal structures of the periplasmic domains of three PCPs that impart substantially different chain length distributions to surface polysaccharides. Despite very low sequence similarities, they have a common protomer structure with a long central -helix extending 100 Å into the periplasm. The protomers self-assemble into bell-shaped oligomers of variable sizes, with a large internal cavity. Electron microscopy shows that one of the full-length PCPs has a similar organization as that observed in the crystal for its periplasmic domain alone. Functional studies suggest that the top of the PCP oligomers is an important region for determining polysaccharide modal length. These structures provide a detailed view of components of the bacterial polysaccharide assembly machinery.Ante Tocilj, Christine Munger, Ariane Proteau, Renato Morona, Leanne Purins, Eunice Ajamian, John Wagner, Magdalene Papadopoulos, Luisa Van Den Bosch, John L Rubinstein, James Féthière, Allan Matte & Miroslaw Cygle