MSCS is a Critical Component for Osmotic Survival of Vibrio Cholerae

Abstract

is an enormous protein essential for hearing, balance, and proper eyesight. There are over 100 mutations in CDH23 that affect these processes with varying severity, some leading to deafness, balance disorders, and progressive blindness (Usher Syndrome). In the inner ear, CDH23 makes up the upper half of a proteinaceous filament known as the tip link, which is essential for hearing. Upon stimulation by sound or head movements, the tip link is stretched and conveys force to open the ion channels in the inner ear, thereby leading to the conversion of vibrational stimulus into electrical signals interpreted by the brain as sound. CDH23 is a non-classical cadherin with 27 extracellular cadherin (EC) repeats and a membrane adjacent domain (MAD28). The EC repeats are connected by a linker region containing highly conserved residues that bind calcium ions essential for tip-link function. Electron microscopy images suggest that CDH23 exists as a cis-homodimer within the tip link, however, the structural elements mediating this dimerization are not well determined. To better understand innerear mechanotransduction at the molecular level, we have solved high-resolution X-ray crystal structures of 18 CDH23 EC repeats along with 13 of the 26 EC linker regions (Jaiganesh et al., 2018). Here, we present several biochemical experiments that suggest potential sites of parallel dimerization on the extracellular domain of CDH23. Additionally, we present structures of various fragments of CDH23 allowing for closer analysis of deafness causing mutations. These results provide information on the cis-homodimerization of CDH23 and provide deeper insights about how mutations can result in inherited deafness.

Polymer-extracted structure of the mechanosensitive channel MscS reveals the role of protein-lipid interactions in the gating cycle

“…The opening and closing transitions were found to be essentially frictionless, non-perturbing, and non-dissipative (Çetiner et al, 2023), indicating that lipid re-arrangement is not possible. The slow inactivation and recovery transitions on the other hand are strongly voltage-dependent, which suggests that inactivation is specifically associated with the rearrangement of the protein-lipid boundary (Britt et al, 2024).…”

“…The opening-closing transitions are sharply tension-dependent and can be very fast (Boer et al, 2011). In contrast, the inactivation and recovery transitions are slow and sensitive to the lipid environment and the nature of lipid-anchoring sidechains (Britt et al, 2024).…”

Turgor and the conformational pathway for MscS recovery

“…Thus, the compacting action of turgor pressing the dome from the inside of the cage will be unopposed. With this regard, the pressure-receiving dome adjacent to the gate region would function as a 'piston' driving the TM3 barrel inside the firmly lipid-anchored TM1-TM2 sheath (Britt et al, 2024). A constant interplay exists between metabolically generated turgor pressure, peptidoglycan elasticity, and membrane area inside the cell.…”

“…While the tension-sensitivity of MscS has been well characterized previously (Belyy et al, 2010b; Britt et al, 2024; Sukharev, 2002), its dependence on normal turgor pressure has not been explored. To address how turgor pressure may influence MscS’s state distribution, we use computational approaches to study its putative conformational transition from the splayed inactivated state to the compact closed state.…”