Elucidation of the zinc binding site in KCNQ channels.

Background and purpose: KCNQ1-5 (Kv7.1-7.5) are members of a family of voltage-gated potassium channels with prominent function in the nervous and cardiovascular systems and in epithelia. KCNQ channels are activated by intracellular free zinc, but the molecular mechanism of this effect is poorly understood and zinc binding sites within KCNQ channels are elusive.

Experimental approach: We used patch-clamp electrophysiology, site-directed mutagenesis and computational biology to investigate the action of zinc on KCNQ1 and its complexes with KCNE1 or KCNE3 auxiliary subunits.

Key results: Zinc ionophores, zinc pyrithione (ZnPy) and pyrrolidinedithiocarbamate (PDTC), potently activated homotetrameric KCNQ1 channels. In contrast, heteromeric KCNQ1/KCNE1 and KCNQ1/KCNE3 channels were partially inhibited by ZnPy. Focussing on this difference, we identified a putative zinc coordination site in close proximity to the KCNQ1-KCNE interface and a binding site for the KCNQ channel cofactor, phosphatidylinositol 4,5-bisphosphate (PIP₂). The zinc coordination site in KCNQ1 contains histidines H126 and H240, and glutamic acid E170. Additional aspartic acid D242 acts as an effector site in coupling zinc binding with channel activation. The site is partially conserved with other KCNQ subunits, although the role of D242 appears to be unique for KCNQ1.

Conclusions and implications: Our findings reveal a new structural modality for ligand-induced activation of an important potassium channel, which can be harnessed for development of KCNQ-targeting pharmaceutics.