The gut's mucus layer is a barrier. Pathogens that get through it reach the epithelial cells underneath and cause infection. Most immune defenses either strengthen the barrier or kill pathogens that breach it. These are separate functions performed by separate molecules.
Intelectin-2 does both. MIT researchers showed that this gut lectin simultaneously crosslinks mucus molecules (strengthening the barrier) and binds to sugar structures on bacterial membranes (trapping and eventually killing the bacteria). One protein, two independent defense mechanisms, operating at the same interface.
The through-claim: the dual function isn't redundancy — it's spatial economy. The mucus layer is thin. Any molecule positioned in the mucus has simultaneous access to both the gel network (which it can strengthen) and to incoming bacteria (which it can trap). Separating these functions into two molecules would require each to occupy the same space — a stacking problem in a layer only tens of microns thick. By combining barrier-strengthening and pathogen-trapping in a single lectin, the gut places both functions at every point in the mucus without requiring twice the molecular machinery.
The antimicrobial activity is broad: Staphylococcus aureus, Klebsiella pneumoniae, including antibiotic-resistant strains. The mechanism — binding bacterial surface sugars, then disrupting the cell membrane over time — exploits a feature that bacteria can't easily evolve away from: they need surface glycans for function. Losing them to evade intelectin-2 would compromise the bacterium's own membrane integrity.
This is defense by colocation. The barrier and the weapon occupy the same molecule because they need to occupy the same space.