TPR motifs: hallmarks of a new polysaccharide export scaffold.

Bacteria produce a remarkable range of surface and secreted polysaccharides. Two pathways have been defined for the biosynthesis and export of capsular polysaccharides and exopolysaccharides in Gram-negative bacteria. A structure of AlgK described in this issue provides structural insight into a third previously unrecognized pathway associated with important biopolymers (Keiski et al., 2010).