After 18 years of guessing, scientists found the gut toxin's doorway — and built a decoy to block it

For nearly two decades, scientists knew a common gut bacterium could help trigger colon cancer — but not how its toxin got its grip on colon cells. Now a Johns Hopkins team, publishing in Nature, has found the missing doorway: a protein called claudin-4, which normally helps seal neighbouring cells together. The toxin, made by Bacteroides fragilis — a bacterium living harmlessly in up to 20% of healthy people — must latch onto claudin-4 before it can break the colon's protective lining and stir the inflammation that can lead to tumours. Better still, the team built a molecular decoy shaped like that doorway, and in mice the decoy soaked up the toxin and protected the colon from damage. It is early work, not yet a treatment for people — but a mystery from 2009 now has both an answer and a possible way to block it.

SDG 3 · Good health and well-being — Mechanism: tech innovation