The usher N terminus is the initial targeting site for chaperone-subunit complexes and participates in subsequent pilus biogenesis events.
Pilus biogenesis on the surface of uropathogenic Escherichia coli requires the chaperone/usher pathway, a terminal branch of the general secretory pathway. In this pathway, periplasmic chaperone-subunit complexes target an outer membrane (OM) usher for subunit assembly into pili and secretion to the cell surface. The molecular mechanisms of protein secretion across the OM are not well understood. Mutagenesis of the P pilus usher PapC and the type 1 pilus usher FimD was undertaken to elucidate the initial stages of pilus biogenesis at the OM. Deletion of residues 2 to 11 of the mature PapC N terminus abolished the targeting of the usher by chaperone-subunit complexes and rendered PapC nonfunctional for pilus biogenesis. Similarly, an intact FimD N terminus was required for chaperone-subunit binding and pilus biogenesis. Analysis of PapC-FimD chimeras and N-terminal fragments of PapC localized the chaperone-subunit targeting domain to the first 124 residues of PapC. Single alanine substitution mutations were made in this domain that blocked pilus biogenesis but did not affect targeting of chaperone-subunit complexes. Thus, the usher N terminus does not function simply as a static binding site for chaperone-subunit complexes but also participates in subsequent pilus assembly events.
Center for Infectious Diseases, Department of Molecular Genetics and Microbiology, Stony Brook University, Stony Brook, New York 11794-5120, USA.
Tony W
TW
Ng
Leyla
L
Akman
Mary
M
Osisami
David G
DG
Thanassi
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D001425:Bacterial Outer Membrane Proteins / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D017124:Conserved Sequence; D004926:Escherichia coli / Q000502:physiology*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D036781:Fimbriae Proteins / Q000235:genetics / Q000378:metabolism; D010861:Fimbriae, Bacterial / Q000378:metabolism*; D005798:Genes, Bacterial; D018832:Molecular Chaperones / Q000378:metabolism*; D008969:Molecular Sequence Data; D009024:Morphogenesis; D016254:Mutagenesis, Insertional; D009154:Mutation; D033903:Periplasmic Proteins / Q000378:metabolism; D018272:Porins / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D025941:Protein Interaction Mapping; D021122:Protein Subunits / Q000378:metabolism; D021381:Protein Transport; D016415:Sequence Alignment; D017384:Sequence Deletion
D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D018832:Molecular Chaperones; D033903:Periplasmic Proteins; D018272:Porins; D021122:Protein Subunits; C111243:atpG protein, E coli; C489283:fimD protein, E coli; C063629:fimD protein, bacteria; D036781:Fimbriae Proteins