The New Kid on the Block: A Specialized Secretion System during Bacterial Sporulation

The transport of proteins across the bacterial cell envelope is mediated by protein complexes called specialized secretion systems. These nanomachines exist in both Gram-positive and Gram-negative bacteria and have been categorized into different types based on their structural components and functi...

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Bibliographic Details
Published in:Trends in microbiology (Regular ed.) 2018-08, Vol.26 (8), p.663-676
Main Authors: Morlot, Cécile, Rodrigues, Christopher D.A.
Format: Article
Language:English
Subjects:
Bacteria
Biochemistry, Molecular Biology
endospores
Gram-negative bacteria
Gram-positive bacteria
Life Sciences
Proteins
ring-building motif
specialized secretion systems
sporulation
Structural Biology
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Summary:The transport of proteins across the bacterial cell envelope is mediated by protein complexes called specialized secretion systems. These nanomachines exist in both Gram-positive and Gram-negative bacteria and have been categorized into different types based on their structural components and function. Interestingly, multiple studies suggest the existence of a protein complex in endospore-forming bacteria that appears to be a new type of specialized secretion system. This protein complex is called the SpoIIIA-SpoIIQ complex and is an exception to the categorical norm since it appears to be a hybrid composed of different parts from well-defined specialized secretion systems. Here we summarize and discuss the current understanding of this complex and its potential role as a specialized secretion system. The A-Q complex likely represents a new class of specialized secretion system that is highly conserved in endospore-forming bacteria. The A-Q complex is required for endospore formation. Mutants exhibit morphological defects and lack physiological potential. The A-Q complex appears to be a hybrid specialized secretion system composed of proteins with homology to those found in type II, type III, and type IV specialized secretion systems. The structure and function of the A-Q complex is not conserved in endospore-forming bacteria, and differences exist between members of the Bacillales and Clostridiales. The A-Q complex highlights the functional diversity of specialized secretion systems.
ISSN:0966-842X
1878-4380
DOI:10.1016/j.tim.2018.01.001