How does miraculin, the taste-modifying glycoprotein, function on the tongue?

It binds to sweet taste receptors only in acidic conditions

Miraculin is categorized as a glycoprotein responsible for the fruit's fame as a natural taste modifier. Its specific mode of action involves interacting directly with the sweet taste receptors situated on the surface of the tongue's taste buds. This interaction, however, is conditional: the miraculin molecule must first bind to these receptors, and this binding only occurs or becomes effective when the surrounding environment is acidic, such as when consuming citric acid or tart berries. Once bound under acidic conditions, the protein triggers the sweet sensation. When the environment becomes neutral or alkaline, the binding is released, and the sweet effect ceases, allowing the original sour taste to be perceived again, which is why the phenomenon is temporary, lasting perhaps one or two hours.