Phage RyR-domain proteins degrade ADPR-based immune signals and fuel NAD synthesis

This study identifies the mycobacteriophage protein RyDEP as a novel glycosidase that degrades stable cyclic ADP-ribose immune signals to neutralize bacterial Thoeris defenses and restore NAD, revealing an unexpected evolutionary link between phage anti-defense mechanisms and animal ryanodine receptor domains.

The Gist

Imagine a bacterial cell as a small fortress under attack by a virus (a phage). To defend itself, the fortress has a sophisticated alarm system called Thoeris.

Here is how the battle plays out, according to the paper:

1. The Alarm System
When the bacteria detects an invader, it takes a common fuel molecule called NAD (think of it as a battery) and snaps it apart to create a special, circular "alarm signal" (called 2'cADPR or 3'cADPR). This signal is like a very loud, persistent siren that tells the bacteria's defense troops to mobilize and stop the virus from copying itself.

2. The Problem: The Unstoppable Siren
Usually, viruses try to sneak around this by building a wall to block the siren (sequestering the signal). However, these specific alarm signals are incredibly tough and stable. Once they are made, they don't just fade away on their own. The paper notes that until now, scientists didn't know of any way for a virus to actually destroy or "turn off" this specific type of siren to stop the alarm.

3. The Virus's Secret Weapon
The researchers discovered a new trick used by a specific virus (mycobacteriophage). This virus carries a special tool called a protein named RyDEP.

• The Action: RyDEP acts like a pair of molecular scissors. It doesn't just block the alarm; it physically cuts the circular signal in half.
• The Result: By cutting the signal, the virus instantly silences the alarm, allowing the infection to proceed.
• The Bonus: When RyDEP cuts the signal, it doesn't just destroy the pieces; it snaps the circular signal back into its original form, NAD. So, the virus not only turns off the defense but also recycles the fuel back into the system.

4. The Surprising Connection
When the scientists looked at the shape of this viral tool (RyDEP) under a microscope, they found something strange. It looks almost exactly like a part of a protein found in animal muscles (specifically, the Ryanodine Receptor, or RyR).

• In animals, this RyR part controls calcium flow to make muscles contract (like when you flex your arm).
• In this virus, the same shape has been repurposed to cut bacterial alarm signals.

5. The Takeaway
The paper shows that viruses have evolved to use these "muscle-control" shaped tools to act as signal shredders. They can tune these tools to either completely destroy the alarm or just hide it, effectively hacking the bacteria's immune system to win the infection.

In short: The bacteria builds a tough, circular alarm to fight viruses. The virus brings a special pair of scissors (RyDEP) that cuts the alarm in half, silencing the defense and recycling the parts, all using a tool that looks suspiciously like a muscle control switch found in animals.

Technical Summary

Technical Summary: Phage RyR-domain proteins degrade ADPR-based immune signals and fuel NAD synthesis

Problem Statement
Bacterial, plant, and animal cells utilize nucleotide immune signals as a conserved defense strategy against viral infection. In bacteria, the Thoeris anti-phage defense system functions by converting nicotinamide adenine dinucleotide (NAD) into cyclic ADP-ribose signals, specifically 2'cADPR and 3'cADPR. These signals activate downstream effectors to restrict viral replication. While phage proteins have been identified that can bind and sequester these Thoeris signals, a critical gap in understanding remained: no known mechanism existed to degrade the exceptionally stable 2'cADPR and 3'cADPR molecules to terminate immune activation. Consequently, the mechanism by which viruses could actively dismantle these specific immune signals to subvert host defense was unknown.

Methodology
To address this gap, the authors employed a forward biochemical screen to identify proteins capable of degrading the stable cyclic ADP-ribose signals. This screen led to the discovery of the mycobacteriophage protein RyDEP. The study utilized structural biology, specifically determining the crystal structure of the RyDEP-3'cADPR complex in a post-cleavage state, to elucidate the molecular basis of the interaction. Furthermore, the researchers characterized the enzymatic activity of RyDEP and investigated the functional diversity of RyDEP proteins across different phages to determine how they modulate immune signaling.

Key Contributions and Results
The study identifies RyDEP as the founding member of a new enzyme family capable of cleaving 2'cADPR and 3'cADPR, thereby inactivating the Thoeris defense system. The research establishes that RyDEP functions as a glycosidase that specifically cleaves the ribose-ribose linkage within these immune signals. This cleavage serves a dual function: it neutralizes the host's immune activation and simultaneously enables the direct restoration of NAD, the precursor molecule consumed during the defense response.

Structural analysis reveals that the RyDEP protein shares surprising homology with the Repeat12 domain of animal ryanodine receptors (RyRs), which are known to regulate calcium flux and muscle contraction. This finding defines RyR-domain proteins as regulators of nucleotide immune signaling. The authors demonstrate that diverse phage RyDEP proteins have evolved to tune the activity of this RyR domain, allowing them to either degrade the immune signals or sequester them, depending on the specific viral strategy.

Significance
This work provides the first known mechanism for the degradation of stable 2'cADPR and 3'cADPR molecules, resolving how viral infection can be terminated in the context of Thoeris defense. By defining RyR-domain proteins as active regulators of nucleotide immune signaling, the study explains a specific molecular strategy viruses employ to subvert host antiviral defenses. The findings highlight a convergent evolutionary link between viral defense countermeasures and animal calcium signaling machinery, offering a new perspective on the molecular arms race between phages and their bacterial hosts.