Dataset Information

Structure and insights into the function of a Ca(2+)-activated Cl(-) channel.

ABSTRACT: Bestrophin calcium-activated chloride channels (CaCCs) regulate the flow of chloride and other monovalent anions across cellular membranes in response to intracellular calcium (Ca(2+)) levels. Mutations in bestrophin 1 (BEST1) cause certain eye diseases. Here we present X-ray structures of chicken BEST1-Fab complexes, at 2.85 Å resolution, with permeant anions and Ca(2+). Representing, to our knowledge, the first structure of a CaCC, the eukaryotic BEST1 channel, which recapitulates CaCC function in liposomes, is formed from a pentameric assembly of subunits. Ca(2+) binds to the channel's large cytosolic region. A single ion pore, approximately 95 Å in length, is located along the central axis and contains at least 15 binding sites for anions. A hydrophobic neck within the pore probably forms the gate. Phenylalanine residues within it may coordinate permeating anions via anion-? interactions. Conformational changes observed near the 'Ca(2+) clasp' hint at the mechanism of Ca(2+)-dependent gating. Disease-causing mutations are prevalent within the gating apparatus.

SUBMITTER: Kane Dickson V

PROVIDER: S-EPMC4454446 | biostudies-literature | 2014 Dec

REPOSITORIES: biostudies-literature

ACCESS DATA

Publications

Structure and insights into the function of a Ca(2+)-activated Cl(-) channel.

Kane Dickson Veronica V Pedi Leanne L Long Stephen B SB

Nature 20141022 7530

Bestrophin calcium-activated chloride channels (CaCCs) regulate the flow of chloride and other monovalent anions across cellular membranes in response to intracellular calcium (Ca(2+)) levels. Mutations in bestrophin 1 (BEST1) cause certain eye diseases. Here we present X-ray structures of chicken BEST1-Fab complexes, at 2.85 Å resolution, with permeant anions and Ca(2+). Representing, to our knowledge, the first structure of a CaCC, the eukaryotic BEST1 channel, which recapitulates CaCC functio ...[more]

PMID: 25337878

Similar Datasets

Project description:Prevailing models postulate that high Ca(2+) selectivity of Ca(2+) release-activated Ca(2+) (CRAC) channels arises from tight Ca(2+) binding to a high affinity site within the pore, thereby blocking monovalent ion flux. Here, we examined the contribution of high affinity Ca(2+) binding for Ca(2+) selectivity in recombinant Orai3 channels, which function as highly Ca(2+)-selective channels when gated by the endoplasmic reticulum Ca(2+) sensor STIM1 or as poorly Ca(2+)-selective channels when activated by the small molecule 2-aminoethoxydiphenyl borate (2-APB). Extracellular Ca(2+) blocked Na(+) currents in both gating modes with a similar inhibition constant (Ki; ~25 µM). Thus, equilibrium binding as set by the Ki of Ca(2+) blockade cannot explain the differing Ca(2+) selectivity of the two gating modes. Unlike STIM1-gated channels, Ca(2+) blockade in 2-APB-gated channels depended on the extracellular Na(+) concentration and exhibited an anomalously steep voltage dependence, consistent with enhanced Na(+) pore occupancy. Moreover, the second-order rate constants of Ca(2+) blockade were eightfold faster in 2-APB-gated channels than in STIM1-gated channels. A four-barrier, three-binding site Eyring model indicated that lowering the entry and exit energy barriers for Ca(2+) and Na(+) to simulate the faster rate constants of 2-APB-gated channels qualitatively reproduces their low Ca(2+) selectivity, suggesting that ion entry and exit rates strongly affect Ca(2+) selectivity. Noise analysis indicated that the unitary Na(+) conductance of 2-APB-gated channels is fourfold larger than that of STIM1-gated channels, but both modes of gating show a high open probability (Po; ~0.7). The increase in current noise during channel activation was consistent with stepwise recruitment of closed channels to a high Po state in both cases, suggesting that the underlying gating mechanisms are operationally similar in the two gating modes. These results suggest that both high affinity Ca(2+) binding and kinetic factors contribute to high Ca(2+) selectivity in CRAC channels.

Project description:BackgroundTransmembrane protein 16A (TMEM16A) Ca2+-activated Cl- channels have diverse physiological functions, such as epithelial secretion of Cl- and fluid and sensation of pain. Recent studies have demonstrated that TMEM16A contributes to the pathogenesis of infectious and non-infectious inflammatory diseases. However, the role of TMEM16A in inflammation has not been clearly elucidated.Aim of reviewIn this review, we aimed to provide comprehensive information regarding the roles of TMEM16A in inflammation by summarizing the mechanisms underlying TMEM16A expression and activation under inflammatory conditions, in addition to exploring the diverse inflammatory signaling pathways activated by TMEM16A. This review attempts to develop the idea that TMEM16A plays a diverse role in inflammatory processes and contributes to inflammatory diseases in a cellular environment-dependent manner.Key scientific concepts of reviewMultiple inflammatory mediators, including cytokines (e.g., interleukin (IL)-4, IL-13, IL-6), histamine, bradykinin, and ATP/UTP, as well as bacterial and viral infections, promote TMEM16A expression and/or activity under inflammatory conditions. In addition, TMEM16A activates diverse inflammatory signaling pathways, including the IP3R-mediated Ca2+ signaling pathway, the NF-κB signaling pathway, and the ERK signaling pathway, and contributes to the pathogenesis of many inflammatory diseases. These diseases include airway inflammatory diseases, lipopolysaccharide-induced intestinal epithelial barrier dysfunction, acute pancreatitis, and steatohepatitis. TMEM16A also plays multiple roles in inflammatory processes by increasing vascular permeability and leukocyte adhesion, promoting inflammatory cytokine release, and sensing inflammation-induced pain. Furthermore, TMEM16A plays its diverse pathological roles in different inflammatory diseases depending on the disease severity, proliferating status of the cells, and its interacting partners. We herein propose cellular environment-dependent mechanisms that explain the diverse roles of TMEM16A in inflammation.

Dataset Information

Structure and insights into the function of a Ca(2+)-activated Cl(-) channel.

Publications

Structure and insights into the function of a Ca(2+)-activated Cl(-) channel.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure