Figure 4.

Hydrophobic packing of αVBS inside the rod domain. (a) The residues of C-helix (706–739) interact closely with the A-helix (660–688) in the initial configuration of the system, forming a highly packed hydrophobic region. (b) As the force is applied to αVBS, hydrophobic interactions start to break from the end of the C-helix close to the CaM domain. First, as the contact between Ile-736 and Leu-665 is disrupted, Val-732 shifts one residue further, distorting its interaction with Leu-669 and forming a new one with Leu-665. The new set of interactions reduces the energy cost for placing the C-helix one residue further along the A-helix. (c) Further pulling of the C-helix against the rod domain dissociatesVal-732 from Leu-665 and puts Ile-729 in contact with Leu-665. These short-term interactions distribute a large amount of energy required for a global conformational change among smaller energy packs provided as thermal atomic motions, which is consistent with the diffusive nature of the biological systems.