Force and twisting moment exerted on the TRP domain. (A) Cytoplasmic view of the channel domain with TRP domain highlighted blue. The radial/parallel direction r_||, angular/tangential direction r_⊥, and direction of positive torque m_z are defined with respect to an isolated TRP domain. (B–D) Radial force (B), tangential force (C), and twisting moment (D) exerted by each chain on the TRP region as a function of vertical displacement (Δz) for the three contact models (black dashed curve, no contact; blue, frictionless contact; and red, rough contact). The gray region in B–D represents displacements before helix–helix contact.