Deciphering the Potential Role of the IVS-Loop in the Voltage-Sensing Mechanism of Prestin in Mammalian Hearing

Introduction: The exceptional sensitivity and frequency selectivity of the mammalian hearing organ is primarily the result of cochlear amplification, a process powered by the electromotility (EM) of cochlear outer hair cells (OHCs). EM is driven by prestin, a membrane protein from the SLC26 family that functions as a voltage-dependent area motor. While prestin is critical for mammalian hearing, its non-mammalian counterparts act as anion transporters and lack specialized area-motor functions. This research explores the evolutionary adaptations that transformed prestin from an ancestral transporter to an area-motor protein, with a particular focus on the intervening sequence (IVS) loop within the STAS domain—a region that has been largely overlooked but may play a crucial role in fine-tuning the sensing or response of prestin to changes in voltage.

Materials and Methods: Through ancestral sequence reconstruction, structural modeling, and molecular dynamics simulations, we explored the structure, dynamics, and interactions of the IVS loop in mammalian and non-mammalian prestin ancestors and representatives.

Results: Our findings suggest that the IVS loop in placental mammals directly interacts with residues near the intracellular cavity of the adjacent monomer, potentially modulating the response of prestin to voltage changes. These interactions could represent a novel mechanism of voltage sensing, distinct from those observed in other proteins.

Discussion: Structural and functional modifications in the IVS loop appear to have been pivotal in reducing ion transport capability while enhancing voltage sensitivity, thereby fine-tuning the motor function essential for cochlear amplification in mammals.