An ankyrin G binding motif mediates TRAAK localization to the axon initial segment

The axon initial segment (AIS) is a critical compartment in neurons. It converts postsynaptic input into action potentials that trigger information transfer to target cells. This process relies on several voltage-gated sodium (Nav) and potassium (Kv) channels that accumulate in high densities at the AIS. Here, we identify the mechanosensitive potassium channel TRAAK (K2P4.1) as a component of the AIS in adult rat hippocampus and in cultured rat hippocampal neurons. We furthermore show that the AIS localization of TRAAK is driven by a C-terminal sequence that bears resemblance to ankyrin G binding motifs previously identified in Nav and Kv channels. Using a single-molecule pull-down (SiMPull) assay we show that TRAAK and ankyrin G interact. We finally demonstrate that specific point mutations within the identified C-terminal sequence hinder both ankyrin G interaction and AIS localization of the channel. Our findings suggest that TRAAK regulates action potential generation at the AIS and highlights the importance of ankyrin G as a central player in the molecular assembly of the AIS.