Talin Rod Mechanical Unfolding: in Silico Study Using Both Boxed and Steered Molecular Dynamics

Talin is an intracellular protein connecting the actin cytoskeleton to the extracellular matrix via transmembrane integrin receptors. Talin consists of head domain, large α-helical rod and dimerization domain. The rod domain consists of 13 subdomains, which are formed by 4 or 5 α-helices. Mechanical stretching of talin rod regulates its function by destroying binding sites located on the molecular surface of the subdomains and exposing buried binding sites for other binding partners. The rod subdomains have varying mechanical stability, where 5-helix R9 is mechanically the strongest and 4-helix R3 is mechanically the weakest. We have studied how talin rod subdomains R9 and R3 unfold, using boxed molecular dynamics (BXD) and steered molecular dynamics (SMD) simulations. The BXD and SMD simulations are conducted using different conditions, implicit solvent and explicit water model respectively. Despite the difference in methods, analysis of unfolding pathways and free energy of unfolding showed that BXD and SMD results are in good agreement, and support a model where the subdomains unfold through stable 3-helix intermediates. The free energy of unfolding suggests that the folded conformation of the subdomains is the most favorable and the 3-helix intermediate can exist only under mechanical load.