Biosynthesis of Capsular Polysaccharides and Exopolysaccharides
Anne N. Reid and Leslie Cuthbertson
from: Bacterial Glycomics: Current Research, Technology and Applications (Edited by: Christopher W. Reid, Susan M. Twine, and Anne N. Reid). Caister Academic Press, U.K. (2012)
Capsular polysaccharides (CPSs) and exopolysaccharides (EPSs) enhance bacterial survival in the environment, contribute to symbiotic interactions between plants and bacteria, and mediate interactions between plant and animal pathogens and their hosts. Bacteria express a wide array of CPS and EPS structures that are assembled by one of three distinct mechanisms. The Wzy-dependent polymerization system is characterized by the synthesis of lipid-linked repeat units in the cytoplasm, and their block-wise polymerization at the periplasmic face of the inner membrane. The resulting polymer is transported across the outer membrane (in Gram-negative organisms) via a channel formed by an outer membrane polysaccharide export (OPX) protein. The ATP-binding cassette (ABC) transporter-dependent system is defined by the synthesis of full-length CPS chains in the cytoplasm, their ABC transporter-dependent export across the inner membrane, and their subsequent transport across the outer membrane, presumably via a channel formed by an OPX protein. In the synthase-dependent system, a single enzyme achieves polymer initiation, synthesis and export across the membrane. This chapter describes these modes of CPS and EPS assembly, highlighting recent findings and identifying areas where further research is warranted read more ...