Researchers have finally figured out how a toxin from a common gut microbe reaches the cells lining our colon. The finding explains a key step that can lead to colorectal cancer and points to a new way to stop the toxin before it harms us.
Gut Bacterium and Its Dangerous Toxin
The bacterium Bacteroides fragilis lives in the intestines of many healthy people. Some strains produce a protein called BFT (Bacteroides fragilis toxin). When BFT gets into colon cells, it can break down a protective barrier and cause long‑lasting inflammation, which may grow into cancer.
The Missing Receptor: Claudin‑4
Scientists at Johns Hopkins and Harvard used a genome‑wide CRISPR screen to see which genes the toxin needs to work. When they turned off each gene one at a time, the protein claudin‑4 stood out. Without claudin‑4, BFT could not stick to colon cells, and the cells stayed safe.
Claudi n‑4 is a protein that normally helps keep cells tightly sealed together. The discovery was surprising because most toxins attach directly to their target without a separate “door‑opener.”
Proof of a Direct Interaction
Biochemists in Barcelona showed that BFT and claudin‑4 form a one‑to‑one pair. This physical binding proves that the toxin first latches onto the receptor before it can cut the cell‑protecting protein E‑cadherin.
Blocking the Toxin with a Molecular Decoy
Using the knowledge about claudin‑4, the team created a soluble version of the protein that acts like a fake door. In mouse experiments, the decoy captured BFT, keeping the toxin away from real colon cells and preventing tissue damage.
These results suggest that drugs designed to mimic claudin‑4, or small molecules that block the binding site, could become new treatments for preventing colon cancer caused by gut bacteria.
What Still Needs to Be Done
Although the researchers proved that BFT binds tightly to claudin‑4, they have not yet visualized the exact 3‑D shape of the partnership. Current AI modeling tools could not resolve the structure, so more detailed imaging work is required.
Future studies will explore the best way to block this interaction in humans, whether with improved decoys, small‑molecule inhibitors, or other biologics.