Biology subjects

Bavi, N.

Publications and source records attributed to Bavi, N..

5 recordsLinked to original sources

bioRxiv2025

Structural Mechanism of Prestin-Membrane Mechanotransduction

Sound frequency discrimination in mammals depends on the conformational transitions of prestin (SLC26A5), the piezoelectric motor in outer hair cells. The mechanism that enables prestins electrically driven interconversion and its dependence on membrane mechanics, remains unresolved. Here, we show that membrane forces represent a strong driver of the same conformational changes generated by transmembrane voltage and stabilized by bound anions. Single particle cryo-EM structures of nanodisc-reconstituted prestin were obtained from varying lipid composition and membrane thickness. These structures show that membrane thinning biases prestin from a compact conformation to a fully expanded conformation, mimicking outer hair cell elongation/contraction during electromotility. In contrast, zebrafish SLC26A5 transporters undergo complete elevator movements with redistribution of areal changes across leaflets. The structures, together with mutagenesis, H/D exchange mass spectrometry data, and NLC measurements, offer a high-resolution understanding of how prestin translates membrane tension into charge and motor movement during sound-evoked vibrations, revealing a process of reciprocal electro-mechanical transduction essential for tuning cochlear amplification.

biophysics↗

bioRxiv2023

Folding of Prestin's Anion-Binding Site and the Mechanism of Outer Hair Cell Electromotility

Prestin responds to transmembrane voltage fluctuations by changing its cross-sectional area, a process underlying the electromotility of outer hair cells and cochlear amplification. Prestin belongs to the SLC26 family of anion transporters yet is the only member capable of displaying electromotility. Prestins voltage-dependent conformational changes are driven by the putative displacement of residue R399 and a set of sparse charged residues within the transmembrane domain, following the binding of a Cl- anion at a conserved binding site formed by amino termini of the TM3 and TM10 helices. However, a major conundrum arises as to how an anion that binds in proximity to a positive charge (R399), can promote the voltage sensitivity of prestin. Using hydrogen-deuterium exchange mass spectrometry, we find that prestin displays an unstable anion-binding site, where folding of the amino termini of TM3 and TM10 is coupled to Cl- binding. This event shortens the TM3-TM10 electrostatic gap, thereby connecting the two helices, resulting in reduced cross-sectional area. These folding events upon anion-binding are absent in SLC26A9, a non-electromotile transporter closely related to prestin. Dynamics of prestin embedded in a lipid bilayer closely match that in detergent micelle, except for a destabilized lipid-facing helix TM6 that is critical to prestins mechanical expansion. We observe helix fraying at prestins anion-binding site but cooperative unfolding of multiple lipid-facing helices, features that may promote prestins fast electromechanical rearrangements. These results highlight a novel role of the folding equilibrium of the anion-binding site, and helps define prestins unique voltage-sensing mechanism and electromotility.

biophysics↗

bioRxiv2022

State-specific morphological deformations of the lipid bilayer explain mechanosensitive gating of MscS ion channels

The force-from-lipids hypothesis of cellular mechanosensation posits that membrane channels open and close in response to changes in the physical state of the lipid bilayer, induced for example by lateral tension. Here, we investigate the molecular basis for this transduction mechanism by studying the mechanosensitive ion channel MscS from Escherichia coli and its eukaryotic homolog, MSL1 from Arabidopsis thaliana. First, we use single-particle cryo-EM to determine the structure of a novel open conformation of wild-type MscS, stabilized in a thinned lipid nanodisc. Compared with the closed state, the structure shows a reconfiguration of helices TM1, TM2 and TM3a, and widening of the central pore. Based on these structures, we examined how the morphology of the lipid bilayer is altered upon gating, using molecular dynamics simulations. The simulations reveal that closed-state MscS causes drastic protrusions in the inner leaflet of the lipid bilayer, both in the absence and presence of lateral tension, and for different lipid compositions. These deformations arise to provide adequate solvation to hydrophobic features of the protein surface in this conformation, and clearly reflect a high energy conformation for the membrane, particularly under tension. Strikingly, these protrusions are largely eradicated upon channel opening. An analogous computational study of open and closed MSL1 recapitulates these findings. The gating equilibrium of MscS channels thus appears to be dictated by two opposing conformational preferences, namely those of the lipid membrane and of the protein structure. We propose a membrane deformation model of mechanosensation, which posits that tension shifts the gating equilibrium towards the conductive state not because it alters the mode in which channel and lipids interact but because it increases the energetic cost of the morphological perturbations in the membrane induced by to the closed state.

biophysics↗

bioRxiv2021

Cryo-EM Structures of Prestin and the Molecular Basis of Outer Hair Cell Electromotility

The voltage-dependent motor protein, Prestin (SLC26A5) is responsible for the electromotive behavior of outer hair cells (OHCs). Here, we determined the structure of dolphin Prestin in six distinct states using single particle cryo-electron microscopy. Structural and functional data suggest that Prestin adopts a unique and complex set of states, tunable by the identity of bound anions. Complexes with the inhibitor salicylate show that it competes for the anion-binding site of Prestin. These conformations reveal a novel mechanism of area expansion that depends on the helix flexibility and conformational transitions at the membrane protein interface and putatively affects the physical state of the surrounding membrane. These observations illuminate the structural basis of Prestin electromotility, a key component of the mammalian cochlear amplifier.

neuroscience↗

bioRxiv2019

Membrane stiffness is a key determinant of E coli MscS channel mechanosensitivity

Prokaryotic mechanosensitive (MS) channels have an intimate relationship with membrane lipids. Membrane lipids may influence channel activity by directly interacting with bacterial MS channels or by influencing the global properties of the membrane such as area stretch and bending moduli. Previous work has implicated membrane stiffness as a key determinant of the mechanosensitivity of E. coli (Ec)MscS. Here we systematically tested this hypothesis using patch fluorometry of azolectin liposomes doped with lipids of increasing area stretch moduli. Increasing DOPE content of azolectin liposomes causes a rightward shift in the tension response curve of EcMscS. These rightward shifts are further magnified by the addition of stiffer forms of PE such as the branched chain lipid DPhPE and the fully saturated lipid DSPE. Furthermore, a comparison of the branched chain lipid DPhPC to the stiffer DPhPE showed a rightward shift in the tension response curve in the presence of the stiffer DPhPE. We show that these changes are not due to changes in membrane bending rigidity as the tension threshold of EcMscS in membranes doped with PC18:1 and PC18:3 are the same, despite a two-fold difference in their bending rigidity. We also show that after prolonged pressure application sudden removal of force in softer membranes causes a rebound reactivation of EcMscS and we discuss the relevance of this phenomenon to bacterial osmoregulation. Collectively, our data demonstrate that membrane stiffness is a key determinant of the mechanosensitivity of EcMscS.

biophysics↗