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The Autotransporter (AT) Family [Function: Biogenesis/Secretion] Seed alignment | Full alignment in OMPdb

The type V secretion pathway encompasses the autotransporter proteins (AT-1), the two-partner secretion system (TPS) and the recently described type AT-2 family of proteins. AT proteins contain their own transporter domain, covalently attached to the C-terminal extremity of the secreted passenger domain. The secreted proteins are exported in a Sec-dependent manner across the inner membrane, after which they cross the outer membrane with the help of their cognate transporters. Translocation appears to be folding-sensitive, indicating that AT passenger domains cross the periplasm and the outer membrane in non-native conformations and fold progressively at the cell surface. A major difference between AT and TPS pathways arises from the manner by which specificity is established between the secreted protein and its transporter. To date, all of the functionally characterized autotransporters have been implicated in bacterial virulence by displaying enzymatic activity (protease, peptidase, lipase, esterase), mediating actin-promoted bacterial motility or acting as adhesins, toxins/cytotoxins, immunomodulatory proteins or, as more recently discovered, permitting maturation of another virulent protein. The structures of several translocator domains have been solved, suggesting that the β-barrel consists of 12 strands. FabF is a new class of secretion system similar to type V secretion in the autotransporter proteins (AT-1), characterized by a C-terminal, 12-stranded beta barrel with a helix-blocked pore in the closed state. However, in the truncated FapF structure, the N terminus exits the barrel on the periplasmic side rather than passing completely through the pore as in autotransporters. Regarding Hapb, it represents the beta barrel domain of self-associating autotransporters (SAATs). SAATs is a set of virulence factors that enhance bacterial biofilm 87. The Haemophilus influenzae Hap SAAT consists of three domains, the residues 1 - 25 correspond to the signal peptide, the residues 26 - 1036 refer to the Haps that called the passenger domain, while the residues 1037 - 1394 form the 14 beta strands at the C-terminal.

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Literature references

Autotransporter and two-partner secretion: delivery of large-size virulence factors by gram-negative bacterial pathogens
Crit Rev Microbiol. 2004;30(4):275-86. doi: 10.1080/10408410490499872.
PMID: 15646401

Type V protein secretion pathway: the autotransporter story
Microbiol Mol Biol Rev. 2004 Dec;68(4):692-744. doi: 10.1128/MMBR.68.4.692-744.2004.
PMID: 15590781

The autotransporter secretion system
Res Microbiol. 2004 Mar;155(2):53-60. doi: 10.1016/j.resmic.2003.10.002.
PMID: 14990256

Crystal structure of a full-length autotransporter
J Mol Biol. 2010 Feb 26;396(3):627-33. doi: 10.1016/j.jmb.2009.12.061. Epub 2010 Jan 11.
PMID: 20060837

Autotransporter passenger domain secretion requires a hydrophobic cavity at the extracellular entrance of the ?-domain pore
Biochem J. 2011 May 1;435(3):577-87. doi: 10.1042/BJ20101548.
PMID: 21306302

Autotransporter structure reveals intra-barrel cleavage followed by conformational changes
Nat Struct Mol Biol. 2007 Dec;14(12):1214-20. doi: 10.1038/nsmb1322. Epub 2007 Nov 11.
PMID: 17994105

Structure of the translocator domain of a bacterial autotransporter
EMBO J. 2004 Mar 24;23(6):1257-66. doi: 10.1038/sj.emboj.7600148. Epub 2004 Mar 11.
PMID: 15014442

Structure of the translocator domain of a bacterial autotransporter
EMBO J. 2004 Mar 24;23(6):1257-66. doi: 10.1038/sj.emboj.7600148. Epub 2004 Mar 11.
PMID: 15014442

Crystal structure of the Haemophilus influenzae Hap adhesin reveals an intercellular oligomerization mechanism for bacterial aggregation
EMBO J. 2011 Aug 12;30(18):3864-74. doi: 10.1038/emboj.2011.279.
PMID: 21841773

Structural determinants of processing and secretion of the Haemophilus influenzae hap protein
Mol Microbiol. 1997 Nov;26(3):505-18. doi: 10.1046/j.1365-2958.1997.5921965.x.
PMID: 9402021

Proteins in this family with 3D-structure


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