Trimeric coiled coils expand the range of strength, toughness and dynamics of coiled coil motifs under shear.

Coiled coils are widespread protein motifs in nature, and promising building blocks for bio-inspired nanomaterials and nanoscale force sensors. Detailed structural insight into their mechanical response is required to understand their role in tissues and to design building blocks for applications. We use all-atom molecular dynamics simulations to elucidate the mechanical response of two types of coiled coils under shear: dimers and trimers. The amino acid sequences of both systems are similar, thus enabling universal (vs. system-specific) features to be identified. The trimer is mechanically more stable - it is both stronger and tougher - than the dimer, withstanding higher forces (127 pN vs. 49 pN at v = 10-3 nm ns-1) and dissipating up to five times more energy before rupture. The deformation mechanism of the trimer at all pull speeds is dominated by progressive helix unfolding. In contrast, at the lowest pull speeds, dimers deform by unfolding/refolding-assisted sliding. The additional helix in the trimer thus both determines the stability of the structure and affects the deformation mechanism, preventing helix sliding. The mechanical response of the coiled coils is not only sensitive to the oligomerization state but also to helix stability: preventing helix unfolding doubles the mechanical strength of the trimer, but decreases its toughness to half. Our results show that coiled coil trimers expand the range of coiled coil responses to an applied shear force. Altering the stability of individual helices against deformation emerges as one possible route towards fine-tuning this response, enabling the use of these motifs as nanomechanical building blocks.