Humanin is a tiny protein that can protect brain cells from the damage caused by amyloid‑beta, a key player in Alzheimer’s. This study shows that zinc ions can attach directly to humanin at a specific cysteine spot, with a binding strength in the low‑micromolar range—about the same as zinc’s interaction with amyloid‑beta itself. While this hints that zinc levels might influence humanin’s protective effects, the work is purely lab‑based and doesn’t give direct dosing advice.

The abnormal accumulation of the peptide amyloid-beta in the form of senile (or amyloid) plaques is one of the hallmarks of Alzheimer's disease (AD). Zinc ions have been implicated in AD and plaques formation. Recently, the peptide humanin has been discovered. Humanin showed neuroprotective activity against amyloid-beta insults. Here the question investigated is if humanin could interact directly with Zn(II). It is shown that Zn(II) and its substitutes Cd(II)/Co(II) bind to humanin via a thiolate bond from the side chain of the single cysteine at position 8. The low intensity of the d-d bands of Co(II)-humanin indicated an octahedral coordination geometry. Titration experiments suggest that Zn(II) binds to humanin with an apparent affinity in the low muM range. This apparent Zn-binding affinity is in the same order as for amyloid-beta and glutathione and could thus be of physiological relevance.