Nonlinear stiffness of NompC gating spring and its implication in mechanotransduction

Cytoskeleton-tethered mechanosensitive channels (MSCs) use compliant gating springs to convert mechanical stimuli into electrical signals for sensations like sound and touch. The mechanical properties of these gating springs are poorly understood. We investigated the homotetrameric NompC channel, which contains long ankyrin-repeat domains (ARDs), using a toehold-mediated strand displacement method to tether single membrane proteins. This method allowed precise force application and extension measurement with optical tweezers. Our results show that a single NompC complex has a low stiffness of ~0.7 piconewtons per nanometer when pulled from one ARD, with stepwise unfolding beginning at ~7 piconewtons, leading to nonlinear stiffness. ARD truncation indicates strong lateral interactions between ARDs. Computational analyses suggest that this nonlinear, low stiffness may regulate NompC's sensitivity, dynamic range, and kinetics in detecting mechanical stimuli. Our findings highlight the role of a compliant, unfolding-refolding gating spring in facilitating a graded response in MSC ion transduction across diverse mechanical stimuli.