Super-resolution microscopy shows how proteins in E. coli bacteria disassemble

Using super-resolution microscopy, an international team of researchers at the Okinawa Institute of Science and Technology Graduate University (OIST) and Stockholm University (Sweden) has shown how the divisome protein complex inside living Escherichia coli (E. coli) cells disassembles after each round of division.

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An important component of fighting the strains of E. coli that can cause illness and—in extreme cases—be deadly is a better understanding of how bacteria divide and multiply. In each bacterium, the divisome governs cell division. The divisome assembles in the middle of the cell to divide the cell and later disassembles to recycle the proteins.

Bill Söderström, OIST postdoctoral scholar and first author of the paper describing the work, explains that the disassembly process was largely unknown, so he and the other members of the research team wanted to see whether the process is random or if there is some higher order to it.

To visualize what happens inside this protein complex, the researchers made the divisome proteins express fluorescence. Then, they looked at pairs of proteins in the complex using super-resolution microscopy to systematically identify when each protein disassembled. The researchers found that the disassembly process occurred in a controlled order that was very similar to that of the assembly process, following a first-in-first-out principle.

"This outlines in which order the proteins disassemble and it is reproducible," says Ulf Skoglund, study author and head of OIST's Structural Cellular Biology Unit. "This is extremely important in helping us to define in which order events are happening."

This technique also allowed the researchers to get initial insights into the way the proteins were organized within the complex and, by extension, how they interacted with each other by identifying an inner and outer ring of different protein groups within the larger complex. The identification of the rings and ordered disassembly process lets the researchers identify where individual proteins are within the bacteria and at what time they stop interacting with each other. Combined, these discoveries are a step towards a more complete understanding of the structure and function of how bacteria divides.

This means that in a world where antibiotic-resistant bacteria is becoming a real problem, this information could be very useful in creating new methods to target harmful bacteria. By understanding the structure and function of the bacterial division machinery, it could help to pinpoint what to target and at what time during the division process.

Full details of the work appear in the journal Molecular Microbiology; for more information, please visit http://dx.doi.org/10.1111/mmi.13400.