title: Structure-function analysis of the self-recognizing Antigen 43 autotransporter protein from Escherichia coli.
abstract: Antigen 43 (Ag43) is a self-recognizing surface adhesin found in most Escherichia coli strains. Expression of Ag43 confers aggregation and fluffing of cells, promotes biofilm formation and is associated with enhanced resistance to antimicrobial agents. Ag43 is an autotransporter protein and consists of two moieties: a transporter, the beta-module, and a passenger domain, the alpha-module. Here we have employed various molecular approaches to probe structure/function aspects of Ag43. An entire family of Ag43 variants was identified. The gene encoding Ag43 (flu) was cloned from a diverse range of E. coli subtypes and found to encode variant proteins with different properties. Several novel variants were identified and characterized that were unable to promote cell-cell aggregation. By employing a combination of linker insertion mutagenesis and domain swapping between clumping and non-clumping variants, we have pinpointed the region of the protein responsible for autoaggregation to be located within the N-terminal one-third of the passenger domain. Our data suggest that ionic interactions between charged residues residing in interacting pairs of Ag43alpha domains may be important for the self-recognition process. Based on its similarity to other related proteins, we predict the passenger, Ag43alpha, domain primarily to consist of an extended beta-helix structure in which numerous repeats or rungs are stacked in parallel orientation in an extended cylindrical formation. Finally, we found that in spite of their different aggregative pattern all Ag43 variants promoted biofilm formation to abiotic surfaces.
authors.affiliation: Microbial Adhesion Group, Center for Biomedical Microbiology, BioCentrum-DTU, bldg. 301, Technical University of Denmark, DK-2800 Lyngby, Denmark. pkl@biocentrum.dtu.dk
authors.forename: Per
authors.initials: P
authors.lastname: Klemm
authors.forename: Louise
authors.initials: L
authors.lastname: Hjerrild
authors.forename: Morten
authors.initials: M
authors.lastname: Gjermansen
authors.forename: Mark A
authors.initials: MA
authors.lastname: Schembri
mesh_terms: D018829:Adhesins, Bacterial / Q000737:chemistry* / Q000235:genetics*; D018830:Adhesins, Escherichia coli; D000595:Amino Acid Sequence; D000942:Antigens, Bacterial / Q000737:chemistry* / Q000235:genetics*; D001089:Arabinose / Q000494:pharmacology; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry* / Q000235:genetics*; D001483:Base Sequence; D001665:Binding Sites; D001692:Biological Transport; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics*; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics*; D014644:Genetic Variation; D005838:Genotype; D007700:Kinetics; D008969:Molecular Sequence Data; D010641:Phenotype; D017433:Protein Structure, Secondary; D015183:Restriction Mapping; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
chemical_list: D018829:Adhesins, Bacterial; D018830:Adhesins, Escherichia coli; D000942:Antigens, Bacterial; D001425:Bacterial Outer Membrane Proteins; D029968:Escherichia coli Proteins; C118376:antigen 43, E coli; D001089:Arabinose