A Trimeric Lipoprotein Assists in Trimeric Autotransporter Biogenesis in Enterobacteria

• Published in: The Journal of biological chemistry 2014-03, Vol.289 (11), p.7388-7398
• Main Authors: Grin, Iwan, Hartmann, Marcus D., Sauer, Guido, Hernandez Alvarez, Birte, Schütz, Monika, Wagner, Samuel, Madlung, Johannes, Macek, Boris, Felipe-Lopez, Alfonso, Hensel, Michael, Lupas, Andrei, Linke, Dirk
• Format: Article
• Language: English
• Subjects: Adhesins, Bacterial - genetics; Adhesins, Bacterial - metabolism; Autotransport; Bacterial Adhesion; Bacterial Pathogenesis; Biological Transport; Cell Separation; Cloning, Molecular; Crystal Structure; DNA Primers; Enterobacteria; Enterobacteriaceae - metabolism; Flow Cytometry; Gram-negative Bacteria; Lipoprotein; Lipoproteins - genetics; Lipoproteins - metabolism; Membrane Insertion; Membrane Trafficking; Microbiology; Models, Molecular; Peptide Library; Periplasm - metabolism; Plasmids - metabolism; Protein Multimerization; Protein Structure, Tertiary; Salmonella - metabolism; Surface Properties
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M113.513275

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 β-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. 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.