Chloride binding to prestin does not influence very high-frequency complex nonlinear capacitance (cNLC) in the mouse...

Area of Science:

• Auditory neuroscience
• Molecular biophysics

Background:

• Prestin (SLC26a5) is crucial for cochlear amplification in mammals, enhancing hearing sensitivity and frequency selectivity.
• Its function relies on voltage-dependent charge movements, known as nonlinear capacitance (NLC).
• Chloride anions were previously thought to regulate prestin kinetics, especially at lower frequencies.

Purpose of the Study:

• To investigate the frequency response of NLC in mouse outer hair cells (OHCs), a species with ultrasonic hearing.
• To determine the role of chloride binding in high-frequency prestin function.
• To explore the factors governing prestin's piezoelectric-like behavior at high frequencies.

Main Methods:

• Studied NLC frequency response in mouse OHCs.
• Utilized molecular dynamics (MD) simulations to assess anion binding in prestin mutants.
• Examined NLC frequency cut-off (F _is ) in S396E knock-in mice.
• Assessed tension sensitivity of NLC in wild-type (WT) and mutant prestin.

Main Results:

• The characteristic frequency cut-off (F _is ) for mouse NLC is approximately 27 kHz.
• Single point mutations (S396E, S398E) in the chloride binding pocket abolished anion susceptibility and binding.
• NLC F _is in S396E knock-in mice remained unaltered, indicating chloride is not key for high-frequency activity.
• Tension sensitivity of NLC in S396E mutants was comparable to WT, suggesting chloride is not allosterically involved in piezoelectric-like behavior.

Conclusions:

• High-frequency prestin function in mice is likely governed by viscoelastic loads within the membrane, not chloride interactions.
• Species-specific auditory requirements for cochlear amplification may involve modifications of external mechanical loads on prestin, rather than its protein-anion interactions.
• Prestin's core structure and anion binding pocket are conserved across species, implying external mechanical factors drive evolutionary adaptations in hearing frequency ranges.