channel connecting the mother cell and forespore during bacterial endospore formation

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 105; no. 39; pp. 15100 - 15105
• Main Authors: Meisner, Jeffrey, Wang, Xin, Serrano, Monica, Henriques, Adriano O, Moran, Charles P. Jr
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 30.09.2008; National Acad Sciences
• Subjects: Amino Acid Sequence; Bacillus subtilis; Bacillus subtilis - cytology; Bacillus subtilis - genetics; Bacillus subtilis - physiology; Bacteria; Bacterial Proteins - genetics; Bacterial Proteins - physiology; Biological Sciences; Biotinylation; Carbon-Nitrogen Ligases - genetics; Cells; Cytoplasm; Cytoplasm - enzymology; Endospores; Escherichia coli Proteins - genetics; Gene expression; Gene Expression Regulation; Membrane proteins; Membrane Proteins - genetics; Membranes; Molecular Sequence Data; Mother cells; Proteins; Repressor Proteins - genetics; Secretion; Sequence Homology, Amino Acid; Sigma Factor - metabolism; Spores; Spores, Bacterial - cytology; Spores, Bacterial - genetics; Spores, Bacterial - physiology; Sporulation
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0806301105

At an early stage during Bacillus subtilis endospore development the bacterium divides asymmetrically to produce two daughter cells. The smaller cell (forespore) differentiates into the endospore, while the larger cell (mother cell) becomes a terminally differentiated cell that nurtures the developing forespore. During development the mother cell engulfs the forespore to produce a protoplast, surrounded by two bilayer membranes, which separate it from the cytoplasm of the mother cell. The activation of σG, which drives late gene expression in the forespore, follows forespore engulfment and requires expression of the spoIIIA locus in the mother cell. One of the spoIIIA-encoded proteins SpoIIIAH is targeted specifically to the membrane surrounding the forespore, through an interaction of its C-terminal extracellular domain with the C-terminal extracellular domain of the forespore membrane protein SpoIIQ. We identified a homologous relationship between the C-terminal domain of SpoIIIAH and the YscJ/FliF protein family, members of which form multimeric rings involved in type III secretion systems and flagella. If SpoIIIAH forms a similar ring structure, it may also form a channel between the mother cell and forespore membranes. To test this hypothesis we developed a compartmentalized biotinylation assay, which we used to show that the C-terminal extracellular domain of SpoIIIAH is accessible to enzymatic modification from the forespore cytoplasm. These and other results lead us to suggest that SpoIIIAH forms part of a channel between the forespore and mother cell that is required for the activation of σG.