The range of human hearing is regulated by the hair cells in the cochlea of the inner ear.
Some cells can pick up high tones, some low tones and so on.
A hair cell's ability to pick up a given frequency is influenced by how quickly potassium ions can move across its membrane. That's affected in turn by two proteins researchers call alpha and beta. Recent work by Johns Hopkins researchers has established that the beta protein plays an especially important role. In lab experiments they've been able to show that its expression within hair cells is regulated. In essence, it shapes the cell's ability to hear within a certain range.