Structural determinants of Kvβ1.3-induced channel inactivation: a hairpin modulated by PIP2

Abstract

Inactivation of voltage-gated Kv1 channels can be altered by Kvbeta subunits, which block the ion-conducting pore to induce a rapid ('N-type') inactivation. Here, we investigate the mechanisms and structural basis of Kvbeta1.3 interaction with the pore domain of Kv1.5 channels. Inactivation induced by Kvbeta1.3 was antagonized by intracellular PIP(2). Mutations of R5 or T6 in Kvbeta1.3 enhanced Kv1.5 inactivation and markedly reduced the effects of PIP(2). R5C or T6C Kvbeta1.3 also exhibited diminished binding of PIP(2) compared with wild-type channels in an in vitro lipid-binding assay. Further, scanning mutagenesis of the N terminus of Kvbeta1.3 revealed that mutations of L2 and A3 eliminated N-type inactivation. Double-mutant cycle analysis indicates that R5 interacts with A501 and T480 of Kv1.5, residues located deep within the pore of the channel. These interactions indicate that Kvbeta1.3, in contrast to Kvbeta1.1, assumes a hairpin structure to inactivate Kv1 channels. Taken together, our findings indicate that inactivation of Kv1.5 is mediated by an equilibrium binding of the N terminus of Kvbeta1.3 between phosphoinositides (PIPs) and the inner pore region of the channel.

Influence of lipids on protein-mediated transmembrane transport

“…Kruse et al (2012) showed that phosphatidylinositol 4,5-bisphosphate (PI(4,5)P 2 ) depletion inhibited K v 7.1 and K v 7/2/7.3 channel current by more than 90%; in contrast to previous work (Decher et al, 2008;Oliver et al, 2004) they did not observe such PIP 2 -dependence in other members of the K v family (Kruse et al, 2012).…”

Dynamic PIP 2 interactions with voltage sensor elements contribute to KCNQ2 channel gating

“…Structural studies on Kir channels (1,2,5) demonstrated that PIP 2 directly interacts with the channels. Subsequent studies supported that PIP 2 also interacts directly with voltage-gated potassium (Kv) channels (6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19). Several positive residues that may be critical for PIP 2 activity have been identified (7,11,18,(20)(21)(22)(23)(24).…”

The molecular basis for the actions of KVβ1.2 on the opening and closing of the KV1.2 delayed rectifier channel

“…For examples, the K V β1.3 N-terminus, unlike K V β1.1, may enter the pore as a hairpin and the inactivation conferred by this subunit and may be modified by the cellular metabolite PIP2. 28 So while some similarity in mechanism seems evident from our data and those of others, there are undoubtedly significant differences, which makes comparative studies among the K V β1 splice variants important in the future.…”

“…Ablation of the unique N-terminus eliminates the negative shift produced by K V β1.2 on K V 1.2, 24 and mutations in K V β1.3 that remove fast inactivation make the shift in K V 1.5 activation less pronounced. 28 Modeling of ionic current data suggests that open channel block by the N-terminus, in addition to causing fast inactivation, can produce saturation of activation at depolarized potentials and thus an apparent negative shift in activation. 29 Slowed channel deactivation is consistent with the inability of the channel gate to close while the K V β1 N-terminus (Fig.…”