Ca²⁺-Calmodulin and PIP2 interactions at the proximal C-terminus of Kv7 channels

Abstract

In the heart, co-assembly of Kv7.1 with KCNE1 produces the slow I potassium current, which repolarizes the cardiac action potential and mutations in human Kv7.1 and KCNE1 genes cause cardiac arrhythmias. The proximal Kv7.1 C-terminus binds calmodulin (CaM) and phosphatidylinositol-4,5-bisphosphate (PIP) and recently we revealed the competition of PIP with the calcified CaM N-lobe to a previously unidentified site in Kv7.1 helix B, also known to harbor a LQT mutation. Data indicated that PIP and Ca-CaM perform the same function on I channel gating to stabilize the channel open state. Here we show that similar features were observed for Kv7.1 currents expressed alone. We also find that conservation of homologous residues in helix B of other Kv7 subtypes confer similar competition of Ca-CaM with PIP2 binding to their proximal C-termini and suggest that PIP2-CaM interactions converge to Kv7 helix B to modulates channel activity in a Kv7 subtype-dependent manner.

Phosphatidylinositol 4,5-bisphosphate (PIP2) regulates KCNQ3 K+ channels by interacting with four cytoplasmic channel domains

“…ing channels (30,31). Because this site is conserved in KCNQ3 (Lys 531 -Lys 532 -Lys 533 ), we independently mutated the three lysines to asparagines and tested them for interaction with PIP 2 using our VSP approach.…”

“…Our experiments show that the triplet of lysines (Lys 531 , Lys 532 , and Lys 533 ) located at the end of the B-helix of KCNQ3 do not interact with PIP 2 . However, Arg 539 and Arg 555 located in the distal C terminus of KCNQ1 (within the C-helix) were reported to decrease the affinity of the channel to DiC8-PIP 2 (26), and Lys 526 , Lys 527 , and Lys 528 have been identified as a critical fifth site where CaM competes with PIP 2 to stabilize the open state of KCNQ1-containing channels (30,31). The possibility of other PIP 2 -interacting sites at the end of the regulatory domain is intriguing, given the location of the site of phosphorylation of KCNQ3 channels by protein kinase C (64), because such phosphorylation would add a counteracting negative charge at that locus.…”

Determining the target of membrane sterols on voltage-gated potassium channels

“…Composition of the membrane lipid environment affects the function of the embedded ion channels. These effects may occur via nonspecific routes by influencing membrane properties like fluidity, lateral forces or curvature, but can also act more specifically via the reorganization of lipid domains, alteration of local electric fields or even through selective lipid-channel interactions where lipids actively participate in gating [1][2][3] . Cholesterol, an essential component of the plasma membrane, is also known to interact with ion channels.…”

Lack of correlation between surface expression and currents in epileptogenic AB-calmodulin binding domain Kv7.2 potassium channel mutants

“…The amino acids corresponding to helices A and B are shadowed in green [6,26]. The CaM binding domains are indicated in blue, while putative residues of Helix A [28,29] and Helix B [30] implicated in the interaction with PIP 2 are boxed in brown. The residues mutated R333 and K526 are in red.…”