December 4th – PhyLife talk by Hridya Valia Madapally

The last PhyLife talk of this semester will be by Hridya Valia Madapally on December 4th. As always the talk willl take place in Lykeion at 11:00 am.

Title: Potassium transport through the intersubunit tunnel of KdpFABC

Abstract: Potassium is an important ion for survival of all forms of life. In bacteria, potassium is essential to maintain membrane potential, pH, and to provide turgor pressure for cell growth and division. When external potassium levels are low, a unique protein called kdpFABC is expressed to transport potassium into the bacterial cells. This unique protein consists of a subunit that descends from the family of potassium channels and another subunit from the family of P-type ATPase pumps. Both the subunits, channel like kdpA and pump like kdpB, are essential for potassium transport. However, the pathway of transport of potassium through the protein has remained elusive. Data from cryo-EM studies suggests that a ~40 Å long tunnel connecting the channel and pump subunit is the course of K+ passage in the protein. However, the identity of the densities found in the tunnel is disputed; it is unclear whether they correspond to K+ ions or water molecules. Employing molecular dynamics simulations, we observe that both K+ ions and water molecules co-exist in the tunnel. Moreover, we notice that there are a few stable binding sites for potassium in the tunnel. However, free energy of potassium transport along the tunnel calculated using enhanced sampling techniques suggests that a large barrier prevents spontaneous diffusion of potassium from the channel to the pump subunit. This investigation shows that there are possibly more intermediate states of the protein that remains to be identified which facilitates the movement of potassium from the channel to the pump through the tunnel.