Biology subjects

Dehghani-Ghahnaviyeh, S.

Publications and source records attributed to Dehghani-Ghahnaviyeh, S..

4 recordsLinked to original sources

bioRxiv2025

Mapping the free energy landscape of K-Ras4B dimerization

KRAS-4B regulates cellular proliferation and differentiation via its GTPase activity, and it is often mutated in human tumors. Deregulation of the MAPK/ERK pathway as a result of K-Ras4B mutations leads to uncontrolled proliferation, with the dimer/multimerization of K-Ras4B on the plasma membrane believed to be the initiating event for subsequent MAPK/ERK signaling. While K-Ras4B proteins are known to cluster on the plasma membrane, whether they associate through well-defined dimerization interfaces remains an open question. Here, we present the dimerization landscape of active, GTP-bound wild-type and G12D mutant K-Ras4B using coarse-grained unbiased and enhanced sampling molecular dynamics simulations. We recover the experimentally-reported K-Ras4B interfaces, and additionally unveil rugged free energy landscapes with many-yet uncharacterized-minima that feature c-Raf-mediated dimerization interfaces. We further explore whether wild-type or G12D K-Ras4B present different dimerization states, revealing that the G12D mutant is more likely to form diverse dimers compared to WT K-Ras4B. Our work presents evidence that K-Ras4B proteins likely interact through multifaceted interfaces that may enable controlled dimerization in different conformations from a single system, efficiently promoting nanoclustering. Although many weak, non-specific interfaces are forming, the most dominant interfaces occur with nanomolar affinity, offering a structural basis for the design of ligands able to modulate K-Ras4B dimers.

biophysics↗

bioRxiv2022

Lipid-mediated organization of prestin in the outer hair cell membrane and its implications in sound amplification

Prestin is a high-density motor protein in the outer hair cells (OHCs), whose conformational response to acoustic signals alters the shape of the cell, thereby playing a major role in sound amplification by the cochlea. Despite recent structural determination in active and inhibited states, the details of prestins intimate interactions with the membrane, which are central to its function remained unresolved. Here, employing a large set (collectively, more than 0.5 ms) of coarse-grained molecule dynamics simulations, we characterize the nature of prestins lipid-protein interactions, demonstrating their impact on the organization of prestin at densities relevant to the OHCs and its effectiveness in reshaping OHCs. Beyond local enrichment/depletion of various lipid types, prestin causes drastic anisotropic membrane deformation, which in turn mediates a preferential membrane organization of prestin in which deformation patterns by neighboring prestin copies are aligned constructively. The reduced membrane rigidity accompanying this arrangement is hypothesized to maximize the mechanical impact of prestin on OHC reshaping during cochlear sound amplification. Prestins preferential arrangement is further verified by extended simulations demonstrating strong correlation between prestin neighbors in their orientations. These results demonstrate a strong case of protein-protein cooperative communication in membrane, purely mediated by their interactions with lipids.

biophysics↗

bioRxiv2022

Structure of C. elegans TMC-1 complex illuminates auditory mechanosensory transduction

The initial step in the sensory transduction pathway underpinning hearing and balance in mammals involves the conversion of force into the gating of a mechanosensory transduction (MT) channel. Despite the profound socioeconomic impacts of hearing disorders and the fundamental biological significance of understanding MT, the composition, structure and mechanism of the MT complex has remained elusive. Here we report the single particle cryo-EM structure of the native MT TMC-1 complex isolated from C. elegans. The 2-fold symmetric complex is composed of 2 copies each of the pore-forming TMC-1 subunit, the calcium-binding protein CALM-1 and the transmembrane inner ear protein TMIE. CALM-1 makes extensive contacts with the cytoplasmic face of the TMC-1 subunits while the single-pass TMIE subunits reside on the periphery of the complex, poised like the handles of an accordion. A subset of particles in addition harbors a single arrestin-like protein, ARRD-6, bound to a CALM-1 domain. Single- particle reconstructions and molecular dynamics simulations show how the MT complex deforms the membrane bilayer and suggest crucial roles for lipid-protein interactions in the mechanism by which mechanical force is transduced to ion channel gating.

biochemistry↗

bioRxiv2022

Protonation-dependent alternating access of a spinster transporter, an emerging family of broad-specificity efflux pumps

Spinster (Spns) lipid transporters are critical for transporting sphingosine-1-phosphate (S1P) across cellular membranes. In humans, Spns2 functions as the main S1P transporter in endothelial cells, making it a potential drug target for modulating S1P signaling. Here, we employed an integrated approach in lipid membranes to identify unknown conformational states of a bacterial Spns from Hyphomonas neptunium (HnSpns) and to define its proton- and substrate-coupled conformational dynamics. Our systematic study reveals conserved residues critical for protonation steps and their regulation, and how sequential protonation of these proton switches coordinates the conformational transitions in the context of a noncanonical ligand-dependent alternating access. A conserved periplasmic salt bridge (Asp60TM2:Arg289TM7) keeps the transporter in a closed conformation, while proton-dependent conformational dynamics are significantly enhanced on the periplasmic side, providing a pathway for ligand exchange. Furthermore, our resistance assays reveal substrate polyspecificity and HnSpns multidrug resistance (MDR) activity that underscore the previously unknown role of Spns proteins in MDR, beyond their activity in sphingolipid transport and signaling.

biophysics↗