Chloride binding does not influence prestin motor speed at very high frequencies in the mouse outer hair cell

Prestin (SLC26A5) promotes mechanical feedback via outer hair cells (OHC) within the organ of Corti, governed by voltage-dependent kinetics of its charge movements; namely, nonlinear-capacitance (NLC). We study NLC frequency response in mouse OHC membrane patches. The characteristic frequency cut-off (F_is) is 27 kHz. Single point mutations within prestin's chloride binding pocket (S396E and S398E) lack usual anion influence. In agreement, we show absence of anion binding in these mutants through molecular dynamics (MD) simulations. NLC F_is in S396E knock-in mice is unaltered, indicating that high frequency activity is not governed by chloride but likely by viscoelastic loads. Also, the allosteric action of chloride does not underlie piezoelectric-like behavior in prestin, since tension sensitivity of S396E NLC is comparable to WT. Because structures of all studied species appear indistinguishable, with analogous chloride binding pockets, prestin performance likely evolved by modifying, not its protein-anion interaction, but instead mechanical loads on the protein.