title: Bacterial outer membrane ushers contain distinct targeting and assembly domains for pilus biogenesis.
abstract: Biogenesis of a superfamily of surface structures by gram-negative bacteria requires the chaperone/usher pathway, a terminal branch of the general secretory pathway. In this pathway a periplasmic chaperone works together with an outer membrane usher to direct substrate folding, assembly, and secretion to the cell surface. We analyzed the structure and function of the PapC usher required for P pilus biogenesis by uropathogenic Escherichia coli. Structural analysis indicated PapC folds as a beta-barrel with short extracellular loops and extensive periplasmic domains. Several periplasmic regions were localized, including two domains containing conserved cysteine pairs. Functional analysis of deletion mutants revealed that the PapC C terminus was not required for insertion of the usher into the outer membrane or for proper folding. The usher C terminus was not necessary for interaction with chaperone-subunit complexes in vitro but was required for pilus biogenesis in vivo. Interestingly, coexpression of PapC C-terminal truncation mutants with the chromosomal fim gene cluster coding for type 1 pili allowed P pilus biogenesis in vivo. These studies suggest that chaperone-subunit complexes target an N-terminal domain of the usher and that subunit assembly into pili depends on a subsequent function provided by the usher C terminus.
authors.affiliation: Center for Infectious Diseases, Department of Molecular Genetics and Microbiology, State University of New York at Stony Brook, 11794-5120, USA. david.thanassi@stonybrook.edu
authors.forename: David G
authors.initials: DG
authors.lastname: Thanassi
authors.forename: Christos
authors.initials: C
authors.lastname: Stathopoulos
authors.forename: Karen
authors.initials: K
authors.lastname: Dodson
authors.forename: Dominik
authors.initials: D
authors.lastname: Geiger
authors.forename: Scott J
authors.initials: SJ
authors.lastname: Hultgren
mesh_terms: D000595:Amino Acid Sequence; D001425:Bacterial Outer Membrane Proteins / Q000378:metabolism; D002942:Circular Dichroism; D018604:Epitope Mapping; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins; D010861:Fimbriae, Bacterial / Q000378:metabolism*; D006801:Humans; D018832:Molecular Chaperones / Q000737:chemistry* / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D008969:Molecular Sequence Data; D018272:Porins / Q000737:chemistry* / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D017422:Sequence Analysis, DNA
chemical_list: D001425:Bacterial Outer Membrane Proteins; D029968:Escherichia coli Proteins; D018832:Molecular Chaperones; D018272:Porins; C111243:atpG protein, E coli