Opening of the Human Epithelial Calcium Channel TRPV6

Ca(2+)-selective transient receptor potential vanilloid subfamily member 6 (TRPV6) channels play a critical role in calcium uptake in epithelial tissues(1–4). Altered TRPV6 expression is associated with a variety of human diseases(5), including cancers(6). TRPV6 channels are constitutively active(1,7,8) and their open probability depends on the lipidic composition of the membrane, increasing significantly in the presence of phosphatidylinositol 4,5-bisphosphate (PIP(2))(7,9). We previously solved crystal structures of detergent-solubilized rat TRPV6 in the closed state(10,11). Corroborating previous electrophysiological studies(3), these structures demonstrated that the Ca(2+) selectivity of TRPV6 arises from a ring of aspartate side chains in the selectivity filter that tightly binds Ca(2+). However, it has remained unknown how TRPV6 channels open and close their pores for ion permeation. Here we present cryo-EM structures of human TRPV6 in the open and closed states. The channel selectivity filter adopts similar conformations in both states, consistent with its explicit role in ion permeation. The iris-like channel opening is accompanied by an α-to-π helical transition in the pore-lining S6 helices at an alanine hinge just below the selectivity filter. As a result of this transition, the S6 helices bend and rotate, exposing different residues to the ion channel pore in the open and closed states. This novel gating mechanism, which defines the constitutive activity of TRPV6, is unique for tetrameric ion channels and provides new structural insights for understanding their diverse roles in physiology and disease.