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The epithelial sodium channel (ENaC) plays a key role in salt and water homeostasis in tetrapod vertebrates. There are four ENaC subunits (α, β, γ, δ), forming heterotrimeric αβγ- or δβγ-ENaCs. Although the physiology of αβγ-ENaC is well understood, for decades the field has stalled with respect to δβγ-ENaC due to the lack of mammalian model organisms. The SCNN1D gene coding for δ-ENaC was previously believed to be absent in rodents, hindering studies using standard laboratory animals. We analyzed all currently available rodent genomes and discovered that SCNN1D is present in rodents but was independently lost in five rodent lineages, including the Muridae (mice and rats). The independent loss of SCNN1D in rodent lineages may be constrained by phylogeny and taxon-specific adaptation to dry habitats, however habitat aridity does not provide a selection pressure for maintenance of SCNN1D across Rodentia. A fusion of two exons coding for a structurally flexible region in the extracellular domain of δ-ENaC appeared in the Hystricognathi (a group that includes guinea pigs). This conserved pattern evolved at least 41 Ma and represents a new autapomorphic feature for this clade. Exon fusion does not impair functionality of guinea pig (Cavia porcellus) δβγ-ENaC expressed in Xenopus oocytes. Electrophysiological characterization at the whole-cell and single-channel level revealed conserved biophysical features and mechanisms controlling guinea pig αβγ- and δβγ-ENaC function as compared with human orthologs. Guinea pigs therefore represent commercially available mammalian model animals that will help shed light on the physiological function of δ-ENaC. ispartof: MOLECULAR BIOLOGY AND EVOLUTION vol:38 issue:12 pages:5704-5725 ispartof: location:United States status: published

Many congenital myasthenic syndromes (CMS) are associated with mutations in the genes encoding the acetylcholine receptor (AChR), an oligomeric protein with the structure alpha(2)betadeltaepsilon. AChR deficiency is frequently due to homozygous or heteroallelic mutations in the AChR epsilon subunit, most of which cause truncation of the polypeptide chain and loss of surface expression of AChR. Here we identified mutations epsilon1369delG and epsilonY458X, located in the 18 amino acid epsilon subunit C-terminus that lies extracellular to the M4 transmembrane domain. We then incorporated green fluorescent protein (GFP) into the intracellular loop between M3 and M4 of mutant or wild-type epsilon subunits and expressed the AChRs in RD or HEK 293 cells. AChR containing wild-type GFP-tagged epsilon subunits were incorporated into the surface membrane, whereas the GFP-tagged AChR mutant epsilon subunits co-localized with an endoplasmic reticulum (ER) marker and were not expressed on the cell surface. In addition, mutant AChRs did not reach the cell surface, as measured by labelling of intact cells with I-125-alpha-bungarotoxin and precipitation with an epsilon-subunit-specific antiserum. Mutagenesis studies showed that cysteine 470, located four amino acids from the C-terminus, is essential for alpha/epsilon assembly and surface expression of adult AChR. Replacement of cysteine 470 by serine does not restore alpha/epsilon assembly or surface expression. Our results provide the first use of GFP-tagged AChR as a tool for investigation of CMS and demonstrate a previously undetermined role for a disulphide-bonded cystine in the epsilon subunit C-terminus, which plays a crucial role in expression of the adult AChR.

Chronic consumption of alcohol by humans has been shown to lead to impairment of executive and cognitive functions. Here we have studied the changes that take place in the dorsal striatum in post-mortem brains of alcoholics and normal controls. The results show a significant change in the expression of both the excitatory ionotropic glutamate receptor and the inhibitory GABA-A receptor subunit genes in the caudate but not the putamen of the striatum. The mRNA levels in the caudate encoding the glutamate receptor subunit GluN2A and the GABA-A receptor subunits δ, ε and ρ2 were significantly decreased whereas the GluD1, GluD2 and the GABA-A γ1 mRNA levels were significantly increased in the alcoholics as compared to controls. Interestingly in controls, 11 glutamate and 5 GABA-A receptor genes were more prominently (fold-increase varied from 1.24 to 2.91) expressed in the caudate than the putamen. We have previously shown in post-mortem samples from alcoholics that the expression level of glutamate and GABA-A receptor genes in the dorsal-lateral prefrontal cortex is similar to that of normal controls (Jin et al., 2011a;Jin et al., 2014b). This is in contrast to the present study. As the caudate is vital for automatic thinking, the results indicate that the balance between voluntary and automatic control of behaviours is altered in alcoholics. Our results suggest that there may be diminished executive control on goal-directed alcohol-seeking behaviour and, rather, a shift to greater striatal control over behaviours that may be critical in the progress of becoming an alcoholic.

F-type and V-type ATPases couple synthesis or hydrolysis of ATP to the translocation of H+ or Na+ across biological membranes and have similarities in structure and mechanism. In both types of enzymes three main parts can be distinguished: headpiece, membrane-bound piece and stalk region. We report on structural details of the membrane sector and stalk region, including the stator, of V-type ATPase from Clostridium fervidus, as determined by electron microscopy. Besides visualization of the stator structure, one of the main findings is that in certain projections the central stalk connecting V-1 and V-0 makes an angle of about 70 degrees with the membrane. Implications for the subunit arrangement in V-type and F-type ATPase are discussed.

The uncharged photoactivable probe 2-[H-3]diazofluorene ([H-3]DAF) was used to examine structural changes in the Torpedo californica nicotinic acetylcholine receptor (AChR) ion channel induced by agonists. Photoincorporation of [H-3]DAF into the AChR consisted of the following two components: a nonspecific component consistent with incorporation into residues situated at the lipid-protein interface, and a specific component, inhibitable by noncompetitive antagonists and localized to the M2 hydrophobic segments of AChR subunits. The nonspecific [3H]DAF incorporation was characterized in the M4 segment of each AChR subunit. The observed distribution and periodicity of labeled residues reinforce the conclusion that the M4 segments are organized as transmembrane a-helices with a common "face" of each helix in contact with lipid, Within the M2 segments, in the absence of agonist [H-3]DAF specifically labeled homologous residues beta Val-261 and delta Val-269, with incorporation into beta Val-269 at a 5-fold greater efficiency than into beta Val-261. This observation, coupled with the lack of detectable incorporation into alpha-M2 including the homologous alpha Val-255, indicates that within the resting channel [H-3]DAF is bound with its photoreactive diazo group oriented toward delta Val-269. In the presence of agonist, there is an similar to 90% reduction in the labeling of beta Val-261 and delta Val-269 accompanied by specific incorporation into residues (beta Leu-257, beta Ala-258, delta Ser-262, and delta Leu-265) situated 1 or 2 turns of an alpha-helix closer to the cytoplasmic end of the M2 segments. The results provide a further characterization of agonist-induced rearrangements of the M2 (ion channel) domain of the AChR.

Many congenital myasthenic syndromes (CMS) are associated with mutations in the genes encoding the acetylcholine receptor (AChR), an oligomeric protein with the structure alpha(2)betadelta epsilon. AChR deficiency is frequently due to homozygous or heteroallelic mutations in the AChR epsilon subunit, most of which cause truncation of the polypeptide chain and loss of surface expression of AChR. Here we identified mutations epsilon 1369delG and epsilon Y458X, located in the 18 amino acid epsilon subunit C-terminus that lies extracellular to the M4 transmembrane domain. We then incorporated green fluorescent protein (GFP) into the intracellular loop between M3 and M4 of mutant or wild-type epsilon subunits and expressed the AChRs in RD or HEK 293 cells. AChR containing wild-type GFP-tagged epsilon subunits were incorporated into the surface membrane, whereas the GFP-tagged AChR mutant epsilon subunits co-localized with an endoplasmic reticulum (ER) marker and were not expressed on the cell surface. In addition, mutant AChRs did not reach the cell surface, as measured by labelling of intact cells with (125)I-alpha-bungarotoxin and precipitation with an epsilon-subunit-specific antiserum. Mutagenesis studies showed that cysteine 470, located four amino acids from the C-terminus, is essential for alpha/epsilon assembly and surface expression of adult AChR. Replacement of cysteine 470 by serine does not restore alpha/epsilon assembly or surface expression. Our results provide the first use of GFP-tagged AChR as a tool for investigation of CMS and demonstrate a previously undetermined role for a disulphide-bonded cystine in the epsilon subunit C-terminus, which plays a crucial role in expression of the adult AChR.

F-type and V-type ATPases couple synthesis or hydrolysis of ATP to the translocation of H+ or Na+ across biological membranes and have similarities in structure and mechanism. In both types of enzymes three main parts can be distinguished: headpiece, membrane-bound piece and stalk region. We report on structural details of the membrane sector and stalk region, including the stator, of V-type ATPase from Clostridium fervidus, as determined by electron microscopy. Besides visualization of the stator structure, one of the main findings is that in certain projections the central stalk connecting V-1 and V-0 makes an angle of about 70 degrees with the membrane. Implications for the subunit arrangement in V-type and F-type ATPase are discussed.

Background Idiopathic Pulmonary Fibrosis (IPF) is an unresolved clinical issue. Phosphodiesterases (PDEs) are known therapeutic targets for various proliferative lung diseases. Lung PDE6 expression and function has received little or no attention. The present study aimed to characterize (i) PDE6 subunits expression in human lung, (ii) PDE6 subunits expression and alteration in IPF and (iii) functionality of the specific PDE6D subunit in alveolar epithelial cells (AECs). Methodology/Principal Findings PDE6 subunits expression in transplant donor (n = 6) and IPF (n = 6) lungs was demonstrated by real-time quantitative (q)RT-PCR and immunoblotting analysis. PDE6D mRNA and protein levels and PDE6G/H protein levels were significantly down-regulated in the IPF lungs. Immunohistochemical analysis showed alveolar epithelial localization of the PDE6 subunits. This was confirmed by qRT-PCR from human primary alveolar type (AT)II cells, demonstrating the down-regulation pattern of PDE6D in IPF-derived ATII cells. In vitro, PDE6D protein depletion was provoked by transforming growth factor (TGF)-β1 in A549 AECs. PDE6D siRNA-mediated knockdown and an ectopic expression of PDE6D modified the proliferation rate of A549 AECs. These effects were mediated by increased intracellular cGMP levels and decreased ERK phosphorylation. Conclusions/Significance Collectively, we report previously unrecognized PDE6 expression in human lungs, significant alterations of the PDE6D and PDE6G/H subunits in IPF lungs and characterize the functional role of PDE6D in AEC proliferation.