Three unrelated viruses have been shown to kill bacteria by trapping the cell wall transporter MurJ, which flips essential components of the bacterial wall across the inner membrane, at the same freezing location.
This common tactic reveals weaknesses in one of bacteria’s most important systems and restructures where new antibiotics might attack.
A virus pattern appears
inside the bacteria filmMurJ normally flips critical wall-building materials to the outside of the cell, a behavior that keeps the protective barrier intact.
By resolving the three viral binding forms of MurJ, Professor William M. Clemons Jr. of the California Institute of Technology (California Institute of Technology) demonstrated that different viral proteins all clamp into the same groove, locking the transporter outward.
In both cases, the protein remains facing outward and is unable to complete the movements necessary to pump out the new one. wall component.
Such repeated interferences at a single site suggest that this exposed position is not coincidental but central to how MurJ can be inhibited.
wall bottleneck
Bacteria remain, so peptidoglycana rigid mesh that gives the bacteria its shape and prevents the cells from bursting, and humans cannot make it.
MurJ processes key wall precursors and moves them from the inside of the membrane to the outside.
When that transporter stalls, the supply of wall fragments stops at the membrane, and the outer wall cannot thicken.
“Peptidoglycan is a unique feature of bacteria that makes it an attractive antibiotic target,” Clemmons said.
Small gene, big damage
To burst out from the host, bacteria-The infected virus must stop building its walls fast enough to destroy the cell.
Some have single-gene lytic proteins (small killers encoded by one gene), which researchers call Sgl.
Instead of creating many tools, Sgl cuts into the membrane and shuts down one important machine like MurJ.
This one-shot strategy allows the virus to succeed with minimal genetic impact and also points scientists toward targets for drugs.
three roads meet
Despite their different genomes, the three Sgls use the same strategy to override MurJ. This is an example of convergent evolution.
Despite the lack of shared sequences, a third lysis protein was derived from an environmental dataset and still matched the same MurJ groove.
“This is the third genome that has evolved distinct peptides to inhibit the same target in a similar way,” Clemons said.
hit the same thing repeatedly target This suggests that this transporter is a weak link, and other viruses may reveal further vulnerabilities.
Freeze MurJ in place
To capture MurJ mid-movement, the team used cryo-EM, a cryo-imaging that maps proteins in detail, to see the gates stay open.
A pocket within the transporter typically opens inward to grab the wall precursor, then swings outward to release the wall precursor.
Each Sgl binds along the groove between two membrane helices, blocking the swirling motion that drives the flip.
These cryo-EM maps highlighted small pockets and charged spots on MurJ that could potentially immobilize drugs made to fit.
Why exposure is important
Gram-negative bacteria, microorganisms with extra outer membranes, and drug molecules often have difficulty reaching the inner wall mechanisms.
In the frozen open pose, MurJ opened toward the space between the two membranes rather than toward the cell interior.
Because the pocket faced that gap, the drug was able to bind without passing through the inner membrane, even though the outer barrier remained.
Such access may make MurJ easier to target than hidden enzymes, but inhibitors still need to tolerate blood and metabolism.
antibiotic blueprint
Drug designers can treat the three SGLs as templates, as each fits snugly into MurJ.
Their binding surfaces outline pockets lined with charged residues, giving chemists a clear point of contact with the target.
Lab screens can now search for small molecules inside those pockets and test whether they stop bacteria from growing.
Safe drugs are rarely made from peptide toxins, so it takes years of chemical research to turn that map into an actual pill.
resistance continues to rise
National Centers for Disease Control and Prevention report It is estimated that more than 35,000 people die each year from resistant infections.
“Tens of thousands of people die from antibiotic-resistant infections every year in the United States alone, and that number is rapidly increasing,” Clemons said.
Worldwide, analysis In 2019, an estimated 1.27 million people died directly related to bacterial drug resistance.
As resistance spreads and new antibiotics are slow to emerge, the targets highlighted by the virus may help keep future infections treatable.
Hidden antibiotic clues
millions of virus Genomes are currently stored in sequence databases, many of which may encode undiscovered SGLs with bacterial weaknesses.
By expressing these small genes in bacteria, labs can observe which cells burst and track target proteins.
New viruses can surface from environmental samples without replicating, and cryo-EM could reveal their tactics.
Every time a virus points out a vulnerable spot in a bacterium, drug developers have another option when old antibiotics no longer work.
From discovery to treatment
A shared viral solution anchors MurJ as a controllable choke point, and its exposed pocket provides a practical blueprint.
Next steps include designing small molecules that hold MurJ in its frozen position and testing whether the bacteria evolve an escape route.
This research nature.
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