Extended Data Fig. 1: Function, biochemistry and structural features of electromotile prestin.

a, Electromotility analysis of HEK293 cells transfected with wild-type dolphin prestin compared to GFP-only transfected cell (Mock-GFP). The cellular displacement was normalized based on the cell largest diameter, d₀ (Fig. 1b). The normalized electromotility was 0.05±02 (n = 6) versus 0.008±0.002 (n = 5) for wild-type prestin and Mock-GFP, respectively. These values were measured at the depolarizing voltage step changing from +120 mV to −120 mV (mean ± SD, is the number of independent cells. One-sided Student t-test, unpaired, P=0.005). b, Size-exclusion chromatography (SEC) curves of the full-length dolphin prestin purified in GDN, run on a Superose 6 column, in high Cl⁻ (red) and SO₄²⁻ (blue) based solution. The fractions indicated by black dotted lines in both represent purified proteins that were used for cryo-EM imaging. c, Purified dolphin prestin cryo-EM samples, run on a Stain-free SDS-PAGE gel, indicating size of ~80 kDa for the full-length prestin monomer (representation of n = 3).d, Topology of dolphin prestin. Different domains are indicated by color; the gate domain is colored in blue, the core domain in red and the C- and N-termini as well as the STAS domain in grey. The transmembrane helices are numbered from 1 to 14. The N- and C-termini as well as the STAS domain are oriented towards the cytoplasm.