title: Coating the surface: a model for expression of capsular polysialic acid in Escherichia coli K1.
abstract: Capsules are well-studied components of the bacterial surface that modulate interactions between the cell and its environment. Generally composed of polysaccharide, they are key virulence determinants in invasive infections in humans and other animals. Genetic determinants involved in capsule expression have been isolated from a number of organisms, but perhaps the best characterized is the kps cluster of Escherichia coli K1. In this review, the current understanding of the functions of the kps gene products is summarized. Further, a proposed mechanistic model for capsule expression is presented and discussed. The model is based on the premise that the numerous components of the kps cluster form a hetero-oligomeric complex responsible for synthesis and concurrent translocation of the capsular polysialic acid through sites of inner and outer membrane fusion. We view the ATP-binding cassette (ABC) transporter, KpsMT, to be central to the functioning of the complex, interacting with the biosynthetic apparatus as well as the extracytoplasmic components of the cluster to co-ordinate synthesis and translocation. The model provides the basis for additional experimentation and reflects emerging similarities among systems responsible for macromolecular export in Gram-negative bacteria.
authors.affiliation: Department of Microbiology and Immunology, University of Rochester Medical Center, New York 14642, USA.
authors.forename: J M
authors.initials: JM
authors.lastname: Bliss
authors.forename: R P
authors.initials: RP
authors.lastname: Silver
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism / Q000648:ultrastructure; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism* / Q000472:pathogenicity; D015870:Gene Expression; D005798:Genes, Bacterial; D006801:Humans; D046911:Macromolecular Substances; D008854:Microscopy, Electron; D008954:Models, Biological; D005810:Multigene Family; D011135:Polysaccharides, Bacterial / Q000096:biosynthesis* / Q000235:genetics; D012794:Sialic Acids / Q000096:biosynthesis* / Q000235:genetics; D014774:Virulence
chemical_list: D018528:ATP-Binding Cassette Transporters; D046911:Macromolecular Substances; D011135:Polysaccharides, Bacterial; D012794:Sialic Acids; C021319:polysialic acid