What they called a “surprising” finding, Johns Hopkins Medicine researchers working with bacteria from freshwater lakes and soil report they have pinned down a protein’s essential role in maintaining the germ’s shape. Since the integrity of a bacterial cell’s outer “envelope” or enclosure is key to its survival, the finding could advance the search for new and better antibiotics.
Their findings were published in the journal mBio.
Their results showed that the deletion of a protein, OpgH, in a model bacterium, Caulobacter crescentus, sets off an event cascade that ultimately splits apart the protective, bubble-like cell envelope, eventually killing the cell. This includes the protein OpgH, an enzyme producing glucose-containing molecules called osmoregulated periplasmic glucans, which are packed in the gelatinous in-between spaces of the protective cell envelope.
In our experiments, when we get rid of the protein OpgH in Caulobacter bacteria, which halts production of OPG sugar molecules, the bacteria can’t survive,
Erin Goley, Ph.D.
While Caulobacter crescentus themselves are non-disease-causing bacteria, the OPGs found abundantly in gram-negative bacteria play a role in antibiotic resistance and disease outcome.
It is, therefore, considered that research to firmly establish the role of sugar molecules in gram-negative bacteria, including Caulobacter, is a step into contributing towards the development of new drugs that target disease-causing bacteria that have OPGs, including Brucella, Pseudomonas, Salmonella, and E. coli.
If the case is that proteins making or modifying these sugar molecules are essential to bacterial survival, Goley notes, they could be good drug targets for antibiotics themselves. Or, in organisms where OPGs aren’t essential, a drug that targets some part of the OPG pathway might sensitize the cells to existing antibiotics, she says.
The investigators dialed down levels of the OpgH protein in Caulobacter using a molecular tool called an inducible promoter to study how this affected the shape of the bacteria cell and how its loss is affecting a signaling pathway known as CenKR, which recognizes and repairs problems in the cell envelope. They also introduced genes to overexpress the protein CenR, resulting in the hyperactivation of the CenKR pathway responsible for cell envelope shape.
CenKR pathway responsible for regulating cell envelope shape.
After dialling up or down the OpgH or CenR proteins, scientists placed the bacteria cells on a pad of gel that prevented them from moving. Then, researchers used a specialized microscope to track their shapes and activities.
We found that they became misshapen as we dialed down the OpgH protein and halted production of sugar OPG molecules, or hyperactivated the CenKR signaling pathway that maintains the cell envelope,
Then we also looked at where some of the molecular players that helped to grow the cell and keep the shape of the cell were located,” she says. “The molecular players were not in the correct locations, suggesting that OpgH and CenR are integral to maintaining the cell’s shape,
We established a model for how either depleting OPGs or activating the signaling pathway affects cell shape and growth,
While characterizing the sugar molecule’s role in Caulobacter’s cell structure is an important first step, Goley cautioned that “it will take some time to develop a complete picture about how they function across gram-negative species of bacteria,
Erin Goley, Ph.D.
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For Caulobacter, the sugar molecules are almost like closed rings; in E. coli, they are more like trees, with branches sticking off of chained structures. Knowing their shape and all of the decorations that associate with the molecules has helped researchers like her to further characterize the cell envelope, she says.
In the next phase of research, we hope to investigate all of the enzymes that make, decorate and break down these molecules — so we can get a full picture of their metabolism and how they maintain the cell envelope,
Once we uncover how these enzymes function, that’s great, because those are things drugs can target.
Erin Goley, Ph.D.
Source: John Hopkins Medicine – News
Journal Reference: Daitch AK, Smith EL, Goley ED.0.OpgH is an essential regulator of Caulobacter morphology. mBio0:e01443-24. DOI: https://doi.org/10.1128/mbio.01443-24
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