Figure 6: All-atom MD simulations of WT and +5G mutant EcMscL models.
(a) Side and top views of WT MscL and +5G MscL in their resting equilibrated states. The TM1 helices in the +5G are slightly more tilted than in the WT model mostly because of the higher degree of freedom of TM1 in the +5G model. (b) Side and top views of WT and +5G MscL after 268 ns of simulation (for force regimen see Methods). The pore of the WT model is much more expanded than in the +5G model. This is because of the significant role of the N terminus in tilting TM1 in the membrane plane and in expanding the pore by driving the movement of TM1 away from the central axis. This ability is diminished by extending the Gly linker between the N terminus and TM1. (c) A surface representation of WT and +5G models in the resting and expanded states from the top. This clearly shows the difference in the degree of expansion. (d) The side and top views of the expanded state of the +5G mutant MscL model. To reach this state, the simulation was run for longer than the WT simulation (additional 5 ns under the high membrane surface tension of 100 mN m−1). (e) Closed (solid red) and expanded (dashed black) pore of WT MscL. (f) Closed (solid red) and expanded (dashed black) pore of +5G MscL. Comparing e,f shows that the upper regions of the +5G model in the closed state are substantially more expanded compared with WT because of an increased tilt of TM1 helices.
