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1.
Klotho is a transmembrane protein expressed primarily in kidney, parathyroid gland, and choroid plexus. The extracellular domain could be cleaved off and released into the systemic circulation. Klotho is in part effective as β-glucuronidase regulating protein stability in the cell membrane. Klotho is a major determinant of aging and life span. Overexpression of Klotho increases and Klotho deficiency decreases life span. Klotho deficiency may further result in hearing loss and cardiac arrhythmia. The present study explored whether Klotho modifies activity and protein abundance of KCNQ1/KCNE1, a K+ channel required for proper hearing and cardiac repolarization. To this end, cRNA encoding KCNQ1/KCNE1 was injected in Xenopus oocytes with or without additional injection of cRNA encoding Klotho. KCNQ1/KCNE1 expressing oocytes were treated with human recombinant Klotho protein (30 ng/ml) for 24 h. Moreover, oocytes which express both KCNQ1/KCNE1 and Klotho were treated with 10 µM DSAL (D-saccharic acid-1,4-lactone), a β-glucuronidase inhibitor. The KCNQ1/KCNE1 depolarization-induced current (IKs) was determined utilizing dual electrode voltage clamp, while KCNQ1/KCNE1 protein abundance in the cell membrane was visualized utilizing specific antibody binding and quantified by chemiluminescence. KCNQ1/KCNE1 channel activity and KCNQ1/KCNE1 protein abundance were upregulated by coexpression of Klotho. The effect was mimicked by treatment with human recombinant Klotho protein (30 ng/ml) and inhibited by DSAL (10 µM). In conclusion, Klotho upregulates KCNQ1/KCNE1 channel activity by 'mainly' enhancing channel protein abundance in the plasma cell membrane, an effect at least partially mediated through the β-glucuronidase activity of Klotho protein.  相似文献   

2.
The aim of the study was to investigate whether Kv7 channels and their ancillary β-subunits, KCNE, are functionally expressed in the human urinary bladder. Kv7 channels were examined at the molecular level and by functional studies using RT-qPCR and myography, respectively. We found mRNA expression of KCNQ1, KCNQ3-KCNQ5 and KCNE1-5 in the human urinary bladder from patients with normal bladder function (n = 7) and in patients with bladder outflow obstruction (n = 3). Interestingly, a 3.4-fold up-regulation of KCNQ1 was observed in the latter. The Kv7 channel subtype selective modulators, ML277 (activator of Kv7.1 channels, 10 μM) and ML213 (activator of Kv7.2, Kv7.4, Kv7.4/7.5 and Kv7.5 channels, 10 μM), reduced the tone of 1 μM carbachol pre-constricted bladder strips. XE991 (blocker of Kv7.1–7.5 channels, 10 μM) had opposing effects as it increased contractions achieved with 20 mM KPSS. Furthermore, we investigated if there is interplay between Kv7 channels and β-adrenoceptors. Using cumulative additions of isoprenaline (β-adrenoceptor agonist) and forskolin (adenylyl cyclase activator) in combination with the Kv7 channel activator and blocker, retigabine and XE991, we did not find interplay between Kv7 channels and β-adrenoceptors in the human urinary bladder. The performed gene expression analysis combined with the organ bath studies imply that compounds that activate Kv7 channels could be useful for treatment of overactive bladder syndrome.  相似文献   

3.
4.
Gastric cancer is the second leading cause of cancer death worldwide. Predisposing factors include achlorhydria, Helicobacter pylori infection, oxyntic atrophy and TFF2-expressing metaplasia. In parietal cells, apical potassium channels comprising the KCNQ1 α subunit and the KCNE2 β subunit provide a K+ efflux current to facilitate gastric acid secretion by the apical H+K+ATPase. Accordingly, genetic deletion of murine Kcnq1 or Kcne2 impairs gastric acid secretion. Other evidence has suggested a role for KCNE2 in human gastric cancer cell proliferation, independent of its role in gastric acidification. Here, we demonstrate that 1-year-old Kcne2 −/− mice in a pathogen-free environment all exhibit a severe gastric preneoplastic phenotype comprising gastritis cystica profunda, 6-fold increased stomach mass, increased Ki67 and nuclear Cyclin D1 expression, and TFF2- and cytokeratin 7-expressing metaplasia. Some Kcne2 −/−mice also exhibited pyloric polypoid adenomas extending into the duodenum, and neoplastic invasion of thin walled vessels in the sub-mucosa. Finally, analysis of human gastric cancer tissue indicated reduced parietal cell KCNE2 expression. Together with previous findings, the results suggest KCNE2 disruption as a possible risk factor for gastric neoplasia.  相似文献   

5.
We showed previously that active PKC-α maintains F0F1-ATPase activity, whereas inactive PKC-α mutant (dnPKC-α) blocks recovery of F0F1-ATPase activity after injury in renal proximal tubules (RPTC). This study tested whether mitochondrial PKC-α interacts with and phosphorylates F0F1-ATPase. Wild-type PKC-α (wtPKC-α) and dnPKC-α were overexpressed in RPTC to increase their mitochondrial levels, and RPTC were exposed to oxidant or hypoxia. Mitochondrial levels of the γ-subunit, but not the α- and β-subunits, were decreased by injury, an event associated with 54% inhibition of F0F1-ATPase activity. Overexpressing wtPKC-α blocked decreases in γ-subunit levels, maintained F0F1-ATPase activity, and improved ATP levels after injury. Deletion of PKC-α decreased levels of α-, β-, and γ-subunits, decreased F0F1-ATPase activity, and hindered the recovery of ATP content after RPTC injury. Mitochondrial PKC-α co-immunoprecipitated with α-, β-, and γ-subunits of F0F1-ATPase. The association of PKC-α with these subunits decreased in injured RPTC overexpressing dnPKC-α. Immunocapture of F0F1-ATPase and immunoblotting with phospho(Ser) PKC substrate antibody identified phosphorylation of serine in the PKC consensus site on the α- or β- and γ-subunits. Overexpressing wtPKC-α increased phosphorylation and protein levels, whereas deletion of PKC-α decreased protein levels of α-, β-, and γ-subunits of F0F1-ATPase in RPTC. Phosphoproteomics revealed phosphorylation of Ser146 on the γ subunit in response to wtPKC-α overexpression. We concluded that active PKC-α 1) prevents injury-induced decreases in levels of γ subunit of F0F1-ATPase, 2) interacts with α-, β-, and γ-subunits leading to increases in their phosphorylation, and 3) promotes the recovery of F0F1-ATPase activity and ATP content after injury in RPTC.  相似文献   

6.
Kv7.1 to Kv7.5 α-subunits belong to the family of voltage-gated potassium channels (Kv). Assembled with the β-subunit KCNE1, Kv7.1 conducts the slowly activating potassium current IKs, which is one of the major currents underlying repolarization of the cardiac action potential. A known regulator of Kv7 channels is the lipid phosphatidylinositol 4,5-bisphosphate (PIP2). PIP2 increases the macroscopic current amplitude by stabilizing the open conformation of 7.1/KCNE1 channels. However, knowledge about the exact nature of the interaction is incomplete. The aim of this study was the identification of the amino acids responsible for the interaction between Kv7.1 and PIP2. We generated 13 charge neutralizing point mutations at the intracellular membrane border and characterized them electrophysiologically in complex with KCNE1 under the influence of diC8-PIP2. Electrophysiological analysis of corresponding long QT syndrome mutants suggested impaired PIP2 regulation as the cause for channel dysfunction. To clarify the underlying structural mechanism of PIP2 binding, molecular dynamics simulations of Kv7.1/KCNE1 complexes containing two PIP2 molecules in each subunit at specific sites were performed. Here, we identified a subset of nine residues participating in the interaction of PIP2 and Kv7.1/KCNE1. These residues may form at least two binding pockets per subunit, leading to the stabilization of channel conformations upon PIP2 binding.  相似文献   

7.
Modulation of voltage-gated potassium (KV) channels by the KCNE family of single transmembrane proteins has physiological and pathophysiological importance. All five KCNE proteins (KCNE1–KCNE5) have been demonstrated to modulate heterologously expressed KCNQ1 (KV7.1) with diverse effects, making this channel a valuable experimental platform for elucidating structure–function relationships and mechanistic differences among members of this intriguing group of accessory subunits. Here, we specifically investigated the determinants of KCNQ1 inhibition by KCNE4, the least well-studied KCNE protein. In CHO-K1 cells, KCNQ1, but not KCNQ4, is strongly inhibited by coexpression with KCNE4. By studying KCNQ1-KCNQ4 chimeras, we identified two adjacent residues (K326 and T327) within the extracellular end of the KCNQ1 S6 segment that determine inhibition of KCNQ1 by KCNE4. This dipeptide motif is distinct from neighboring S6 sequences that enable modulation by KCNE1 and KCNE3. Conversely, S6 mutations (S338C and F340C) that alter KCNE1 and KCNE3 effects on KCNQ1 do not abrogate KCNE4 inhibition. Further, KCNQ1-KCNQ4 chimeras that exhibited resistance to the inhibitory effects of KCNE4 still interact biochemically with this protein, implying that accessory subunit binding alone is not sufficient for channel modulation. These observations indicate that the diverse functional effects observed for KCNE proteins depend, in part, on structures intrinsic to the pore-forming subunit, and that distinct S6 subdomains determine KCNQ1 responses to KCNE1, KCNE3, and KCNE4.  相似文献   

8.
1. The molecular weights of the subunits of purified pig heart pyruvate dehydrogenase complex were determined by sodium dodecyl sulphate/polyacrylamide-disc-gel electrophoresis and were: pyruvate decarboxylase, α-subunit 40600, β-subunit 35100; dihydrolipoyl acetyltransferase 76100; dihydrolipoyl dehydrogenase 58200. 2. Inactivation of the pyruvate dehydrogenase complex by its integral kinase corresponded to the incorporation of 0.46nmol of P/unit of complex activity inactivated. 3. Further incorporation of phosphate into the complex occurred to a limit of 1.27nmol of P/unit of complex inactivated (approx. 3 times that required for inactivation). 4. Phosphate was incorporated only into the α-subunit of the decarboxylase. 5. The molar ratio of phosphate to α-subunits of the decarboxylase was estimated by radioamidination of amino groups of pyruvate dehydrogenase [32P]phosphate complex by using methyl [1-14C]acetimidate, followed by separation of α-subunits by sodium dodecyl sulphate/polyacrylamide-disc-gel electrophoresis. Inactivation of the complex (0.46nmol of P/unit of complex inactivated) corresponded to a molar ratio of one phosphate group per two α-chains (i.e. one phosphate group/α2β2 tetramer). Complete phosphorylation corresponded to three phosphate groups per α2β2 tetramer. 6. Subunit molar ratios in the complex were also estimated by the radioamidination technique. Results corresponded most closely to molar ratios of 4 α-subunits:4 β-subunits:2 dihydrolipoyl acetyltransferase subunits:1 dihydrolipoyl dehydrogenase subunit.  相似文献   

9.
In many mammalian neurons, fidelity and robustness of action potential generation and conduction depends on the co-localization of voltage-gated sodium (Nav) and KCNQ2/3 potassium channel conductance at the distal axon initial segment (AIS) and nodes of Ranvier in a ratio of ∼40 to 1. Analogous “anchor” peptides within intracellular domains of vertebrate KCNQ2, KCNQ3, and Nav channel α-subunits bind Ankyrin-G (AnkG), thereby mediating concentration of those channels at AISs and nodes of Ranvier. Here, we show that the channel anchors bind at overlapping but distinct sites near the AnkG N terminus. In pulldown assays, the rank order of AnkG binding strength is Nav1.2 ≫ KCNQ3 > KCNQ2. Phosphorylation of KCNQ2 and KCNQ3 anchor domains by protein kinase CK2 (CK2) augments binding, as previously shown for Nav1.2. An AnkG fragment comprising ankyrin repeats 1 through 7 (R1–7) binds phosphorylated Nav or KCNQ anchors robustly. However, mutational analysis of R1–7 reveals differences in binding mechanisms. A smaller fragment, R1–6, exhibits much-diminished KCNQ3 binding but binds Nav1.2 well. Two lysine residues at the tip of repeat 2–3 β-hairpin (residues 105–106) are critical for Nav1.2 but not KCNQ3 channel binding. Another dibasic motif (residues Arg-47, Arg-50) in the repeat 1 front α-helix is crucial for KCNQ2/3 but not Nav1.2 binding. AnkG''s alternatively spliced N terminus selectively gates access to those sites, blocking KCNQ but not Nav channel binding. These findings suggest that the 40:1 Nav:KCNQ channel conductance ratio at the distal AIS and nodes arises from the relative strength of binding to AnkG.  相似文献   

10.
Domain fusion between SNF1-related kinase subunits during plant evolution   总被引:9,自引:0,他引:9  
Members of the conserved SNF1/AMP-activated protein kinase (AMPK) family regulate cellular responses to environmental and nutritional stress in eukaryotes. Yeast SNF1 and animal AMPKs form a complex with regulatory SNF4/AMPKγ and SIP1/SIP2/GAL83/AMPKβ subunits. The β-subunits function as target selective adaptors that anchor the catalytic kinase and regulator SNF4/γ-subunits to their kinase association (KIS) and association with the SNF1 complex (ASC) domains. Here we demonstrate that plant SNF1-related protein kinases (SnRKs) interact with an adaptor-regulator protein, AKINβγ, in which an N-terminal KIS domain characteristic of β-subunits is fused with a C-terminal region related to the SNF4/AMPKγ proteins. AKINβγ is constitutively expressed in plants, suppresses the yeast Δsnf4 mutation, and shows glucose-regulated interaction with the Arabidopsis SnRK, AKIN11. Our results suggest that evolution of AKINβγ reflects a unique function of SNF1-related protein kinases in plant glucose and stress signalling.  相似文献   

11.
Members of the P4 subfamily of P-type ATPases are believed to catalyze flipping of phospholipids across cellular membranes, in this way contributing to vesicle biogenesis in the secretory and endocytic pathways. P4-ATPases form heteromeric complexes with Cdc50-like proteins, and it has been suggested that these act as β-subunits in the P4-ATPase transport machinery. In this work, we investigated the role of Cdc50-like β-subunits of P4-ATPases for targeting and function of P4-ATPase catalytic α-subunits. We show that the Arabidopsis P4-ATPases ALA2 and ALA3 gain functionality when coexpressed with any of three different ALIS Cdc50-like β-subunits. However, the final cellular destination of P4-ATPases as well as their lipid substrate specificity are independent of the nature of the ALIS β-subunit they were allowed to interact with.  相似文献   

12.
The amiloride-sensitive epithelial Nachannel (ENaC) is a heteromultimeric channel made of three αβγ subunits. The structures involved in the ion permeation pathway have only been partially identified, and the respective contributions of each subunit in the formation of the conduction pore has not yet been established. Using a site-directed mutagenesis approach, we have identified in a short segment preceding the second membrane-spanning domain (the pre-M2 segment) amino acid residues involved in ion permeation and critical for channel block by amiloride. Cys substitutions of Gly residues in β and γ subunits at position βG525 and γG537 increased the apparent inhibitory constant (K i) for amiloride by >1,000-fold and decreased channel unitary current without affecting ion selectivity. The corresponding mutation S583 to C in the α subunit increased amiloride K i by 20-fold, without changing channel conducting properties. Coexpression of these mutated αβγ subunits resulted in a nonconducting channel expressed at the cell surface. Finally, these Cys substitutions increased channel affinity for block by externalZn2+ ions, in particular the αS583C mutant showing a K i for Zn2+of 29 μM. Mutations of residues αW582L or βG522D also increased amiloride K i, the later mutation generating a Ca2+blocking site located 15% within the membrane electric field. These experiments provide strong evidence that αβγ ENaCs are pore-forming subunits involved in ion permeation through the channel. The pre-M2 segment of αβγ subunits may form a pore loop structure at the extracellular face of the channel, where amiloride binds within the channel lumen. We propose that amiloride interacts with Na+ions at an external Na+binding site preventing ion permeation through the channel pore.  相似文献   

13.
GABA type A receptors (GABAAR), the brain''s major inhibitory neurotransmitter receptors, are the targets for many general anesthetics, including volatile anesthetics, etomidate, propofol, and barbiturates. How such structurally diverse agents can act similarly as positive allosteric modulators of GABAARs remains unclear. Previously, photoreactive etomidate analogs identified two equivalent anesthetic-binding sites in the transmembrane domain at the β+ subunit interfaces, which also contain the GABA-binding sites in the extracellular domain. Here, we used R-[3H]5-allyl-1-methyl-5-(m-trifluoromethyl-diazirynylphenyl) barbituric acid (R-mTFD-MPAB), a potent stereospecific barbiturate anesthetic, to photolabel expressed human α1β3γ2 GABAARs. Protein microsequencing revealed that R-[3H]mTFD-MPAB did not photolabel the etomidate sites at the β+ subunit interfaces. Instead, it photolabeled sites at the α+ and γ+ subunit interfaces in the transmembrane domain. On the (+)-side, α1M3 was labeled at Ala-291 and Tyr-294 and γ2M3 at Ser-301, and on the (−)-side, β3M1 was labeled at Met-227. These residues, like those in the etomidate site, are located at subunit interfaces near the synaptic side of the transmembrane domain. The selectivity of R-etomidate for the β+ interface relative to the α++ interfaces was >100-fold, whereas that of R-mTFD-MPAB for its sites was >50-fold. Each ligand could enhance photoincorporation of the other, demonstrating allosteric interactions between the sites. The structural heterogeneity of barbiturate, etomidate, and propofol derivatives is accommodated by varying selectivities for these two classes of sites. We hypothesize that binding at any of these homologous intersubunit sites is sufficient for anesthetic action and that this explains to some degree the puzzling structural heterogeneity of anesthetics.  相似文献   

14.
15.
Long QT interval syndrome (LQTS) type 1 (LQT1) has been reported to arise from mutations in the S3 domain of KCNQ1, but none of the seven S3 mutations in the literature have been characterized with respect to trafficking or biophysical deficiencies. Surface channel expression was studied using a proteinase K assay for KCNQ1 D202H/N, I204F/M, V205M, S209F, and V215M coexpressed with KCNE1 in mammalian cells. In each case, the majority of synthesized channel was found at the surface, but mutant IKs current density at +100 mV was reduced significantly for S209F, which showed ∼75% reduction over wild type (WT). All mutants except S209F showed positively shifted V1/2’s of activation and slowed channel activation compared with WT (V1/2 = +17.7 ± 2.4 mV and τactivation of 729 ms at +20 mV; n = 18). Deactivation was also accelerated in all mutants versus WT (126 ± 8 ms at −50 mV; n = 27), and these changes led to marked loss of repolarizing currents during action potential clamps at 2 and 4 Hz, except again S209F. KCNQ1 models localize these naturally occurring S3 mutants to the surface of the helices facing the other voltage sensor transmembrane domains and highlight inter-residue interactions involved in activation gating. V207M, currently classified as a polymorphism and facing lipid in the model, was indistinguishable from WT IKs. We conclude that S3 mutants of KCNQ1 cause LQTS predominantly through biophysical effects on the gating of IKs, but some mutants also show protein stability/trafficking defects, which explains why the kinetic gain-of-function mutation S209F causes LQT1.  相似文献   

16.
F1-ATPase is a rotary molecular machine with a subunit stoichiometry of α3β3γ1δ1ε1. It has a robust ATP-hydrolyzing activity due to effective cooperativity between the three catalytic sites. It is believed that the central γ rotor dictates the sequential conformational changes to the catalytic sites in the α3β3 core to achieve cooperativity. However, recent studies of the thermophilic Bacillus PS3 F1-ATPase have suggested that the α3β3 core can intrinsically undergo unidirectional cooperative catalysis (T. Uchihashi et al., Science 333:755-758, 2011). The mechanism of this γ-independent ATP-hydrolyzing mode is unclear. Here, a unique genetic screen allowed us to identify specific mutations in the α and β subunits that stimulate ATP hydrolysis by the mitochondrial F1-ATPase in the absence of γ. We found that the F446I mutation in the α subunit and G419D mutation in the β subunit suppress cell death by the loss of mitochondrial DNA (ρo) in a Kluyveromyces lactis mutant lacking γ. In organello ATPase assays showed that the mutant but not the wild-type γ-less F1 complexes retained 21.7 to 44.6% of the native F1-ATPase activity. The γ-less F1 subcomplex was assembled but was structurally and functionally labile in vitro. Phe446 in the α subunit and Gly419 in the β subunit are located on the N-terminal edge of the DELSEED loops in both subunits. Mutations in these two sites likely enhance the transmission of catalytically required conformational changes to an adjacent α or β subunit, thereby allowing robust ATP hydrolysis and cell survival under ρo conditions. This work may help our understanding of the structural elements required for ATP hydrolysis by the α3β3 subcomplex.  相似文献   

17.
G protein–coupled receptors (GPCRs) transduce their signals through trimeric G proteins, inducing guanine nucleotide exchange on their Gα-subunits; the resulting Gα-GTP transmits the signal further inside the cell. GoLoco domains present in many proteins play important roles in multiple trimeric G protein–dependent activities, physically binding Gα-subunits of the Gαi/o class. In most cases GoLoco binds exclusively to the GDP-loaded form of the Gα-subunits. Here we demonstrate that the poly-GoLoco–containing protein Pins of Drosophila can bind to both GDP- and GTP-forms of Drosophilao. We identify Pins GoLoco domain 1 as necessary and sufficient for this unusual interaction with Gαo-GTP. We further pinpoint a lysine residue located centrally in this domain as necessary for the interaction. Our studies thus identify Drosophila Pins as a target of Gαo-mediated GPCR receptor signaling, e.g., in the context of the nervous system development, where Gαo acts downstream from Frizzled and redundantly with Gαi to control the asymmetry of cell divisions.  相似文献   

18.
Assembly of voltage-dependent Ca2+ channels (VDCCs) with their associated proteins regulates the coupling of VDCCs with upstream and downstream cellular events. Among the four isoforms of the Rab3-interacting molecule (RIM1 to -4), we have previously reported that VDCC β-subunits physically interact with the long α isoform of the presynaptic active zone scaffolding protein RIM1 (RIM1α) via its C terminus containing the C2B domain. This interaction cooperates with RIM1α-Rab3 interaction to support neurotransmitter exocytosis by anchoring vesicles in the vicinity of VDCCs and by maintaining depolarization-triggered Ca2+ influx as a result of marked inhibition of voltage-dependent inactivation of VDCCs. However, physiological functions have not yet been elucidated for RIM3 and RIM4, which exist only as short γ isoforms (γ-RIMs), carrying the C-terminal C2B domain common to RIMs but not the Rab3-binding region and other structural motifs present in the α-RIMs, including RIM1α. Here, we demonstrate that γ-RIMs also exert prominent suppression of VDCC inactivation via direct binding to β-subunits. In the pheochromocytoma PC12 cells, this common functional feature allows native RIMs to enhance acetylcholine secretion, whereas γ-RIMs are uniquely different from α-RIMs in blocking localization of neurotransmitter-containing vesicles near the plasma membrane. γ-RIMs as well as α-RIMs show wide distribution in central neurons, but knockdown of γ-RIMs attenuated glutamate release to a lesser extent than that of α-RIMs in cultured cerebellar neurons. The results suggest that sustained Ca2+ influx through suppression of VDCC inactivation by RIMs is a ubiquitous property of neurons, whereas the extent of vesicle anchoring to VDCCs at the plasma membrane may depend on the competition of α-RIMs with γ-RIMs for VDCC β-subunits.  相似文献   

19.
The ζ subunit is a novel inhibitor of the F1FO-ATPase of Paracoccus denitrificans and related α-proteobacteria. It is different from the bacterial (ϵ) and mitochondrial (IF1) inhibitors. The N terminus of ζ blocks rotation of the γ subunit of the F1-ATPase of P. denitrificans (Zarco-Zavala, M., Morales-Ríos, E., Mendoza-Hernández, G., Ramírez-Silva, L., Pérez-Hernández, G., and García-Trejo, J. J. (2014) FASEB J. 24, 599–608) by a hitherto unknown quaternary structure that was first modeled here by structural homology and protein docking. The F1-ATPase and F1-ζ models of P. denitrificans were supported by cross-linking, limited proteolysis, mass spectrometry, and functional data. The final models show that ζ enters into F1-ATPase at the open catalytic αEE interface, and two partial γ rotations lock the N terminus of ζ in an “inhibition-general core region,” blocking further γ rotation, while the ζ globular domain anchors it to the closed αDPDP interface. Heterologous inhibition of the F1-ATPase of P. denitrificans by the mitochondrial IF1 supported both the modeled ζ binding site at the αDPDP/γ interface and the endosymbiotic α-proteobacterial origin of mitochondria. In summary, the ζ subunit blocks the intrinsic rotation of the nanomotor by inserting its N-terminal inhibitory domain at the same rotor/stator interface where the mitochondrial IF1 or the bacterial ϵ binds. The proposed pawl mechanism is coupled to the rotation of the central γ subunit working as a ratchet but with structural differences that make it a unique control mechanism of the nanomotor to favor the ATP synthase activity over the ATPase turnover in the α-proteobacteria.  相似文献   

20.
In the process of developing safer general anesthetics, isomers of anesthetic ethers and barbiturates have been discovered that act as convulsants and inhibitors of γ-aminobutyric acid type A receptors (GABAARs) rather than potentiators. It is unknown whether these convulsants act as negative allosteric modulators by binding to the intersubunit anesthetic-binding sites in the GABAAR transmembrane domain (Chiara, D. C., Jayakar, S. S., Zhou, X., Zhang, X., Savechenkov, P. Y., Bruzik, K. S., Miller, K. W., and Cohen, J. B. (2013) J. Biol. Chem. 288, 19343–19357) or to known convulsant sites in the ion channel or extracellular domains. Here, we show that S-1-methyl-5-propyl-5-(m-trifluoromethyl-diazirynylphenyl) barbituric acid (S-mTFD-MPPB), a photoreactive analog of the convulsant barbiturate S-MPPB, inhibits α1β3γ2 but potentiates α1β3 GABAAR responses. In the α1β3γ2 GABAAR, S-mTFD-MPPB binds in the transmembrane domain with high affinity to the γ+ subunit interface site with negative energetic coupling to GABA binding in the extracellular domain at the β+ subunit interfaces. GABA inhibits S-[3H]mTFD-MPPB photolabeling of γ2Ser-280 (γM2–15′) in this site. In contrast, within the same site GABA enhances photolabeling of β3Met-227 in βM1 by an anesthetic barbiturate, R-[3H]methyl-5-allyl-5-(m-trifluoromethyl-diazirynylphenyl)barbituric acid (mTFD-MPAB), which differs from S-mTFD-MPPB in structure only by chirality and two hydrogens (propyl versus allyl). S-mTFD-MPPB and R-mTFD-MPAB are predicted to bind in different orientations at the γ+ site, based upon the distance in GABAAR homology models between γ2Ser-280 and β3Met-227. These results provide an explanation for S-mTFD-MPPB inhibition of α1β3γ2 GABAAR function and provide a first demonstration that an intersubunit-binding site in the GABAAR transmembrane domain binds negative and positive allosteric modulators.  相似文献   

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