MD Simulations of KirBac1.1 Mutants Reveal Gating Changes at the Bundle Crossing Region

Inwardly rectifying potassium (Kir) channels play important physiological roles in a variety of cells including heart rate, insulin secretion or fluid balance. Their importance is further illustrated by the fact that inherited mutations are linked to diseases including Andersen Tawil Syndrome, Bartter syndrome or neonatal diabetes. Their activity is controlled by dynamical conformational changes that regulate ion flow through the central pore of Kir channels. Understanding the dynamical rearrangements of Kir channels during activation gating requires not only high-resolution structure information from channels crystallized in different conformations but insight into the transition steps. Guided by mutations that are known to increase channel activity (1), molecular dynamics simulations of the WT KirBac1.1 crystal structure and the G143E mutant have been performed. Full atomistic MD simulations revealed that introducing a glutamate in position 143 causes significant widening of the pore. In all our simulations the bundle crossing opened to 17 A compared to the WT. Comparison of the mutant KirBac1.1 with the open structure of KirBac3.1 reveals that the pore radius reaches identical values. Furthermore the global rearrangements including a rotation and a bending of the lower part of TM2 are identical in both structures, suggesting that the final structure of the G143E mutant after 60 ns represents an open conformation. Simulations further revealed that deprotonation is essential for channel opening. This is further supported by investigations with non-charged amino acids in this position, which do not lead to channel opening on the nanosecond time scale.(1) Paynter, J. J., Andres-Enguix, I., Fowler, P. W., Tottey, S., Cheng, W., Enkvetchakul, D., Bavro, V. N., Kusakabe, Y., Sansom, M. S. P., Robinson, N. J., Nichols, C. G., and Tucker, S. J. (2010) J. Biol. Chem 285, 40754-40761.