Mechano-electrical transduction components TMC1-CIB2 undergo a Ca²⁺-induced conformational change linked to hearing loss

TMC1, a unique causative gene associated with deafness, exhibits variants with autosomal dominant and recessive inheritance patterns. TMC1 codes for the transmembrane channel-like protein 1 (TMC1), a key component of the mechano-electrical transduction (MET) machinery for hearing. However, the molecular mechanism of Ca²⁺ regulation in MET remains unclear. Calcium and integrin-binding protein 2 (CIB2), another MET component associated with deafness, can bind with Ca²⁺. Our study shows that TMC1-CIB2 complex undergoes a Ca²⁺-induced conformational change. We identified a vertebrate-specific binding site on TMC1 that interacts with apo CIB2, linked with hearing loss. Using an ex vivo mouse organotypic cochlea model, we demonstrated that disruption of the calcium-binding site of CIB2 perturbs the MET channel conductivity. After systematically analyzing the hearing loss variants, we observed dominant mutations of TMC1 cluster around the putative ion pore or at the binding interfaces with CIB2. These findings elucidate the molecular mechanisms underlying TMC1-linked hearing loss.