Two N-Terminal Domains of Kv4 K+ Channels Regulate Binding to and Modulation by KChIP1

Abstract

The family of calcium binding proteins called KChIPs associates with Kv4 family K(+) channels and modulates their biophysical properties. Here, using mutagenesis and X-ray crystallography, we explore the interaction between Kv4 subunits and KChIP1. Two regions in the Kv4.2 N terminus, residues 7-11 and 71-90, are necessary for KChIP1 modulation and interaction with Kv4.2. When inserted into the Kv1.2 N terminus, residues 71-90 of Kv4.2 are also sufficient to confer association with KChIP1. To provide a structural framework for these data, we solved the crystal structures of Kv4.3N and KChIP1 individually. Taken together with the mutagenesis data, the individual structures suggest that that the Kv4 N terminus is required for stable association with KChIP1, perhaps through a hydrophobic surface interaction, and that residues 71-90 in Kv4 subunits form a contact loop that mediates the specific association of KChIPs with Kv4 subunits.

Kv channel-interacting proteins as neuronal and non-neuronal calcium sensors

“…Important structural determinants of KChIP function and EF-hand-mediated divalent cation binding affinities. (A) Crystal structure of the free KChIP1 monomer (PDB 1S1E) [31] viewed from two different sides. Upper picture: N-terminus on the left (structure starts at position 38) and EF-hands visible; EF1 (black) is non-functional, and EF2 (blue) is occuopied by Mg 2+ under physiological conditions.…”

“…Definitely, more research is needed to elucidate the role of Ca 2+ in Kv4/KChIP complex formation. In this regard it should also be noted that both the Kv4 N-terminus and the Kv4 tetramerization (T1) domain contribute to KChIP binding [31,74], and each KChIP subunit interacts with the N-terminus of one and the T1-domain of a neighboring Kv4 α-subunit [30,75]. It is possible that the Ca 2+ dependencies of KChIP binding to these two sites differ.…”

The Diversity of Calcium Sensor Proteins in the Regulation of Neuronal Function

“…The residues involved in the interaction of the myristoyl group with the hydrophobic pocket are also conserved in the other members of the NCS family, however not all of the other family members display this Ca 2þ /myristoyl switch (O'Callaghan et al 2002;Stephen et al 2007). NCS-1 and KChIP1 expose a similar hydrophobic surface upon Ca 2þ -binding, which could be similarly important for target interactions (Bourne et al 2001;Scannevin et al 2004;Zhou et al 2004b;Pioletti et al 2006). In contrast, other NCS proteins are able to interact with certain binding proteins in the absence of Ca 2þ and therefore Ca 2þ -driven exposure of a hydrophobic surface cannot be the sole mechanism by which these proteins bind to effectors.…”

Mg2+ and Ca2+ Differentially Regulate DNA Binding and Dimerization of DREAM

“…A characteristic feature of DREAM and the NCS family is the sequence CPXG (Cys-104 and Pro-105, see Fig. 1) that prevents the binding of Ca 2ϩ to the first EF-hand (EF-1) as seen in the crystal structures of recoverin (18), KChIP1 (19,20), neurocalcin (21), and frequenin (22). The second EF-hand (EF-2) of DREAM contains aspartate (Asp-150) instead of the usual glutamate at the 12-position of the EF-hand binding loop (Fig.…”