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

Inactivation of voltage-gated Kv1 channels can be altered by Kv beta subunits, which block the ion-conducting pore to induce a rapid ('N-type') inactivation. Here, we investigate the mechanisms and structural basis of Kv beta 1.3 interaction with the pore domain of Kv1.5 channels. Inactivation induced by Kv beta 1.3 was antagonized by intracellular PIP(2). Mutations of R5 or T6 in Kv beta 1.3 enhanced Kv1.5 inactivation and markedly reduced the effects of PIP(2). R5C or T6C Kv beta 1.3 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 Kv beta 1.3 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 Kv beta 1.3, in contrast to Kv beta 1.1, 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 Kv beta 1.3 between phosphoinositides (PIPs) and the inner pore region of the channel.