Alternative splicing modulates Kv channel clustering through a molecular ball and chain mechanism

Abstract

Ion channel clustering at the post-synaptic density serves a fundamental role in action potential generation and transmission. Here, we show that interaction between the Shaker Kv channel and the PSD-95 scaffold protein underlying channel clustering is modulated by the length of the intrinsically disordered C terminal channel tail. We further show that this tail functions as an entropic clock that times PSD-95 binding. We thus propose a 'ball and chain' mechanism to explain Kv channel binding to scaffold proteins, analogous to the mechanism describing channel fast inactivation. The physiological relevance of this mechanism is demonstrated in that alternative splicing of the Shaker channel gene to produce variants of distinct tail lengths resulted in differential channel cell surface expression levels and clustering metrics that correlate with differences in affinity of the variants for PSD-95. We suggest that modulating channel clustering by specific spatial-temporal spliced variant targeting serves a fundamental role in nervous system development and tuning.

A mechanistic framework for studying Kv channel clustering

“…Finally, tail length was found to time Kv channel-PSD-95 complex formation without affecting complex lifetime. These observations mirror evidence obtained for the case of fast channel inactivation 6 and indicate that the Kv channel N-and C-terminal tails function as entropic clocks [5][6][7] to respectively time Kv channel fast inactivation and binding to the PSD-95 scaffold protein.…”

“…Whereas the 'chain' module primarily controls the change in entropy (S) of the binding reaction, the 'chain'-tethered 'ball' sequence primarily determines the change in enthalpy (H) of the reaction 5 . These 'ball' and 'chain' sequence modules were further found to determine the respective association and dissociation kinetics of the recognition motif to and from its receptor site 5,6 . Based on these observations, we suggested a thermodynamic signature of entropy- The 'ball and chain' description for Kv channel binding to a scaffold protein provides a mechanistic framework for studying Kv channel clustering, in a manner analogous to that employed for the study of Kv channel fast inactivation.…”

Entropic clocks in the service of electrical signaling: ‘Ball and chain’ mechanisms for ion channel inactivation and clustering

“…(c) PSD‐95‐mediated Kv channel clustering at unique sites may be achieved by the multiple ‘ball and chain’ interactions, dictated by the stoichiometry of the interaction and the ability of PSD‐95 to multimerize. Panels a and b were reproduced from Ref [22]. with permission.…”

“…Five years later, evidence began to accumulate demonstrating that the Shaker Kv channel protein makes use of a second entropic clock chain for binding to membrane‐associated PSD‐95 synaptic scaffold proteins[20–22] as may be described by analogous ‘ball and chain’ mechanism (Fig. 1b).…”

“…This interaction underlies the clustering of many Kv channel molecules at unique membrane sites[23–26], a process important for efficient electrical signaling[25,27,28]. Here, however, the interaction involves the cytoplasmic C ‐terminal tail of the channel[22–24]. Similar to its N ‐terminal‐based counterpart, the C ‐type ‘ball and chain’ mechanism relies on a channel tail that is comprised of an extended ‘chain’ bearing a conserved PDZ‐recognition motif at its tip (the ‘ball’), usually 4–8 residues in length, able to bind PDZ domains of PSD‐95 scaffold protein partners (Fig.…”