title: Structure of the translocator domain of a bacterial autotransporter.
abstract: Autotransporters are virulence-related proteins of Gram-negative bacteria that are secreted via an outer-membrane-based C-terminal extension, the translocator domain. This domain supposedly is sufficient for the transport of the N-terminal passenger domain across the outer membrane. We present here the crystal structure of the in vitro-folded translocator domain of the autotransporter NalP from Neisseria meningitidis, which reveals a 12-stranded beta-barrel with a hydrophilic pore of 10 x 12.5 A that is filled by an N-terminal alpha-helix. The domain has pore activity in vivo and in vitro. Our data are consistent with the model of passenger-domain transport through the hydrophilic channel within the beta-barrel, and inconsistent with a model for transport through a central channel formed by an oligomer of translocator domains. However, the dimensions of the pore imply translocation of the secreted domain in an unfolded form. An alternative model, possibly covering the transport of folded domains, is that passenger-domain transport involves the Omp85 complex, the machinery required for membrane insertion of outer-membrane proteins, on which autotransporters are dependent.
authors.affiliation: Department of Crystal and Structural Chemistry, Bijvoet Center for Biomolecular Research, Utrecht University, Utrecht, The Netherlands.
authors.forename: Clasien J
authors.initials: CJ
authors.lastname: Oomen
authors.forename: Peter
authors.initials: P
authors.lastname: van Ulsen
authors.forename: Patrick
authors.initials: P
authors.lastname: van Gelder
authors.forename: Maya
authors.initials: M
authors.lastname: Feijen
authors.forename: Jan
authors.initials: J
authors.lastname: Tommassen
authors.forename: Piet
authors.initials: P
authors.lastname: Gros
mesh_terms: D000595:Amino Acid Sequence; D002511:Cephalosporins / Q000494:pharmacology; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression; D026901:Membrane Transport Proteins / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009345:Neisseria meningitidis / Q000201:enzymology* / Q000235:genetics; D011485:Protein Binding; D017510:Protein Folding; D020673:Protein Renaturation; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D012697:Serine Endopeptidases / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D002511:Cephalosporins; D026901:Membrane Transport Proteins; C480853:NalP protein, Neisseria meningitidis; D012697:Serine Endopeptidases; C021720:nitrocefin