Mgm1 is a member of the dynamin family of GTPbinding proteins. Mgm1 was first identified in yeast, where it affects mitochondrial morphology. The human homologue of Mgm1 is called OPA1. Mutations in the OPA1 gene are the prevailing cause of dominant optic atrophy, a hereditary disease in which progressive degeneration of the optic nerve can lead to blindness. Here we investigate the properties of the Mgm1/OPA1 protein in mammalian cells. We find that Mgm1/OPA1 is localized to the mitochondrial intermembrane space, where it is tightly bound to the outer surface of the inner membrane. Overexpression of wild type or mutant forms of the Mgm1/OPA1 protein cause mitochondria to fragment and, in some cases, cluster near the nucleus, whereas the loss of protein caused by small interfering RNA (siRNA) leads to dispersal of mitochondrial fragments throughout the cytosol. The cristae of these fragmented mitochondria are disorganized. At early time points after transfection with Mgm1/OPA1 siRNA, the mitochondria are not yet fragmented. Instead, the mitochondria swell and stretch, after which they form localized constrictions similar to the mitochondrial abnormalities observed during the early stages of apoptosis. These abnormalities might be the earliest effects of losing Mgm1/OPA1 protein.

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We determined structures of the wild-type human PANX1 (PANX1(WT)) in the presence of EDTA, Ca 2+ or K + . These structures are indistinguishable, suggesting that Ca 2+ or K + is unlikely to directly activate PANX1. To study the location and role of the CTT and the N-terminal helix (NTH), we cleaved the CTT from the PANX1(WT) and from an NTH-truncation mutant using caspase 7, and determined their structures (PANX1(ΔCTT) and PANX1(ΔNTH/ΔCTT), respectively). We also determined structures of PANX1 bound to CBX (CBX-PANX1(ΔCTT) and CBX-PANX1(ΔNTH/ ΔCTT)). To study the role of N-glycosylation of PANX1, we investigated the structure of a glycosylation-deficient mutant (N255A), which yielded both gap junctions (PANX1(N255A) Gap ) and hemichannels (PANX1(N255A) Hemi ). The structural determination is detailed in the Methods, and the results are summarized in Extended Data Tables 1-3. The structure of PANX1(ΔCTT) has the highest overall quality (map available at the Electron Microscopy Data Bank (EMD-21589) and model at the Protein Data Bank (6WBG)), and is therefore the reference structure for the discussion throughout the text unless otherwise noted.The PANX1 channel forms a heptamer that contains (from top to bottom) an extracellular domain (ECD), a transmembrane domain (TMD) and an intracellular domain (ICD), with the unstructured CTT

Primary aldosteronism is the most common and curable form of secondary arterial hypertension. We performed whole-exome sequencing in patients with early-onset primary aldosteronism and identified a de novo heterozygous c.71G>A/p.Gly24Asp mutation in the CLCN2 gene, encoding the voltage-gated ClC-2 chloride channel , in a patient diagnosed at 9 years of age. Patch-clamp analysis of glomerulosa cells of mouse adrenal gland slices showed hyperpolarization-activated Cl currents that were abolished in Clcn2 mice. The p.Gly24Asp variant, located in a well-conserved 'inactivation domain', abolished the voltage- and time-dependent gating of ClC-2 and strongly increased Cl conductance at resting potentials. Expression of ClC-2 in adrenocortical cells increased expression of aldosterone synthase and aldosterone production. Our data indicate that CLCN2 mutations cause primary aldosteronism. They highlight the important role of chloride in aldosterone biosynthesis and identify ClC-2 as the foremost chloride conductor of resting glomerulosa cells.