Pivotal Roles of the Outer Membrane Polysaccharide Export and Polysaccharide Copolymerase Protein Families in Export of Extracellular Polysaccharides in Gram-Negative Bacteria

Leslie Cuthbertson, Iain L. Mainprize, James Henderson Naismith, Chris Whitfield

Research output: Contribution to journalReview articlepeer-review

177 Citations (Scopus)

Abstract

Many bacteria export extracellular polysaccharides (EPS) and capsular polysaccharides (CPS). These polymers exhibit remarkably diverse structures and play important roles in the biology of free-living, commensal, and pathogenic bacteria. EPS and CPS production represents a major challenge because these high-molecular-weight hydrophilic polymers must be assembled and exported in a process spanning the envelope, without compromising the essential barrier properties of the envelope. Emerging evidence points to the existence of molecular scaffolds that perform these critical polymer-trafficking functions. Two major pathways with different polymer biosynthesis strategies are involved in the assembly of most EPS/CPS: the Wzy-dependent and ATP-binding cassette (ABC) transporter-dependent pathways. They converge in an outer membrane export step mediated by a member of the outer membrane auxiliary (OMA) protein family. OMA proteins form outer membrane efflux channels for the polymers, and here we propose the revised name outer membrane polysaccharide export (OPX) proteins. Proteins in the polysaccharide copolymerase (PCP) family have been implicated in several aspects of polymer biogenesis, but there is unequivocal evidence for some systems that PCP and OPX proteins interact to form a transenvelope scaffold for polymer export. Understanding of the precise functions of the OPX and PCP proteins has been advanced by recent findings from biochemistry and structural biology approaches and by parallel studies of other macromolecular trafficking events. Phylogenetic analyses reported here also contribute important new insight into the distribution, structural relationships, and function of the OPX and PCP proteins. This review is intended as an update on progress in this important area of microbial cell biology.

Original languageEnglish
Pages (from-to)155-
Number of pages24
JournalMicrobiology and Molecular Biology Reviews
Volume73
Issue number1
DOIs
Publication statusPublished - Mar 2009

Keywords

  • ESCHERICHIA-COLI K-12
  • VIBRIO-CHOLERAE O139
  • ENTEROBACTERIAL COMMON ANTIGEN
  • SECONDARY STRUCTURE PREDICTION
  • COILED-COIL REGIONS
  • SYMBIOTICALLY IMPORTANT EXOPOLYSACCHARIDE
  • GROUP-1 CAPSULAR POLYSACCHARIDES
  • LIPOPOLYSACCHARIDE O-ANTIGEN
  • COLANIC ACID BIOSYNTHESIS
  • EFFLUX TRANSPORTER ACRB

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