Science1 publisherNot yet confirmed elsewhere2 min readPublished
Bacteria sense phage attack when a viral protease cuts their CBASS sensor
University of Utah Health researchers found that the bacterial immune system CBASS fires when a phage's own protease cuts a host sensor protein. It identifies the exact molecular step a phage would have to evade.
The Scientist · Science desk
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What happened
- CBASS's answer is drastic: it mounts a last-resort response that kills the infected cell before the virus can spread to neighbouring bacteria.
- The sensor it depends on is a CD-NTase enzyme, which once activated builds the nucleotide signals that launch the defence.
- That trigger sets CBASS apart from related antiviral systems, which switch on only when they detect a virus's genetic material.
- The team reports the phage's prohead protease is a widespread way to switch these sensors on, a general mechanism across phages.
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Why it matters
- constraint The sensor is tuned to a protein the virus needs to survive, so a phage cannot slip past CBASS by shedding the enzyme.
- precedent Because CBASS is one of the most common bacterial defences, a phage engineered to handle it would travel across many hosts rather than clearing one strain.
- capability Bacteria run through generations fast, giving researchers a quick system to settle immune-mechanism questions before moving to models closer to people.
Phages are being pushed as treatments for bacterial infections, especially the strains antibiotics no longer clear [1]. The trouble is that a phage does not meet a defenceless target: bacteria carry their own systems against viruses, and a phage can be shut down before it does any good [2].
What the team worked out is how one of those systems recognises that an attack is under way. "We found that the protease from the phage actually acts directly on the host protein, and that is the signal that turns on the whole signaling pathway," said Sam Hobbs, an assistant professor of biochemistry at University of Utah Health [9][5].
The result is in Science, in a paper titled "Phage proteases activate CBASS antiphage immunity" [4]. It identifies the trigger but does not describe a phage engineered to get past the defence, and the researchers present the move from a sensing pathway to a better therapy as their stated hope; the paper stops short of reporting it [16].
The pathway reaches past bacteria. CBASS resembles an immune pathway in humans, and the team takes that as a sign it has been maintained since bacteria and people shared a common ancestor [12]. "The fact that these systems are conserved between bacteria and humans suggests that they've been maintained in these different organisms for that entire evolutionary trajectory," Hobbs said [13].
What to watch
- Whether anyone can engineer a phage that keeps a working prohead protease yet avoids tripping the CD-NTase sensor.
- Which bacterial species and phages the protease trigger holds across, given the team calls it widespread.
- Whether the human relative of CBASS is switched on the same way, now that bacteria offer a quick test system.