Real time dynamics of gating-related conformational changes in CorA.

CorA, a divalent-selective channel in the metal ion transport superfamily, is the major Mg-influx pathway in prokaryotes. CorA structures in closed (Mg-bound), and open (Mg-free) states, together with functional data showed that Mg-influx inhibits further Mg-uptake completing a regulatory feedback loop. While the closed state structure is a symmetric pentamer, the open state displayed unexpected asymmetric architectures. Using high-speed atomic force microscopy (HS-AFM), we explored the Mg-dependent gating transition of single CorA channels: HS-AFM movies during Mg-depletion experiments revealed the channel's transition from a stable Mg-bound state over a highly mobile and dynamic state with fluctuating subunits to asymmetric structures with varying degree of protrusion heights from the membrane. Our data shows that at Mg-concentration below K, CorA adopts a dynamic (putatively open) state of multiple conformations that imply structural rearrangements through hinge-bending in TM1. We discuss how these structural dynamics define the functional behavior of this ligand-dependent channel.