A Trimeric Lipoprotein Assists in Trimeric Autotransporter Biogenesis in Enterobacteria

Autor(en): Grin, Iwan
Hartmann, Marcus D.
Sauer, Guido
Hernandez Alvarez, Birte
Schuetz, Monika
Wagner, Samuel
Madlung, Johannes
Macek, Boris
Felipe-Lopez, Alfonso
Hensel, Michael 
Lupas, Andrei
Linke, Dirk
Stichwörter: ADHESINS; Autotransport; Bacterial Adhesion; Bacterial Pathogenesis; Biochemistry & Molecular Biology; COILED-COIL; Crystal Structure; ENTERICA SEROVAR TYPHIMURIUM; Enterobacteria; EXPRESSION; GRAM-NEGATIVE BACTERIA; IDENTIFICATION; Lipoprotein; Membrane Insertion; Membrane Trafficking; PREDICTION; PROTEIN; SERVER; SYSTEM
Erscheinungsdatum: 2014
Volumen: 289
Ausgabe: 11
Startseite: 7388
Seitenende: 7398
Background: Autotransporter adhesins reach the bacterial cell surface by a complex mechanism. Results: In the case of the autotransporter SadA from Salmonella, a lipoprotein assists in surface display. Conclusion: The similarity to eukaryotic MATH domains suggests that the lipoprotein assists in trimerization of SadA. Significance: Understanding the similarities between autotransport systems might lead to new ways of inhibiting bacterial adhesion. Trimeric autotransporter adhesins (TAAs) are important virulence factors of many Gram-negative bacterial pathogens. TAAs form fibrous, adhesive structures on the bacterial cell surface. Their N-terminal extracellular domains are exported through a C-terminal membrane pore; the insertion of the pore domain into the bacterial outer membrane follows the rules of -barrel transmembrane protein biogenesis and is dependent on the essential Bam complex. We have recently described the full fiber structure of SadA, a TAA of unknown function in Salmonella and other enterobacteria. In this work, we describe the structure and function of SadB, a small inner membrane lipoprotein. The sadB gene is located in an operon with sadA; orthologous operons are only found in enterobacteria, whereas other TAAs are not typically associated with lipoproteins. Strikingly, SadB is also a trimer, and its co-expression with SadA has a direct influence on SadA structural integrity. This is the first report of a specific export factor of a TAA, suggesting that at least in some cases TAA autotransport is assisted by additional periplasmic proteins.
DOI: 10.1074/jbc.M113.513275

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