Review. SUR1: a unique ATP-binding cassette protein that functions as an ion channel regulator.
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ABSTRACT:
SUBMITTER: Aittoniemi J
PROVIDER: S-EPMC2674095 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:The mechanism of adenosine triphosphate (ATP)-sensitive potassium (K(ATP)) channel activation by Mg-nucleotides was studied using a mutation (G334D) in the Kir6.2 subunit of the channel that renders K(ATP) channels insensitive to nucleotide inhibition and has no apparent effect on their gating. K(ATP) channels carrying this mutation (Kir6.2-G334D/SUR1 channels) were activated by MgATP and MgADP with an EC(50) of 112 and 8 µM, respectively. This activation was largely suppressed by mutation of the Walker A lysines in the nucleotide-binding domains of SUR1: the remaining small (?10%), slowly developing component of MgATP activation was fully inhibited by the lipid kinase inhibitor LY294002. The EC(50) for activation of Kir6.2-G334D/SUR1 currents by MgADP was lower than that for MgATP, and the time course of activation was faster. The poorly hydrolyzable analogue MgATP?S also activated Kir6.2-G334D/SUR1. AMPPCP both failed to activate Kir6.2-G334D/SUR1 and to prevent its activation by MgATP. Maximal stimulatory concentrations of MgATP (10 mM) and MgADP (1 mM) exerted identical effects on the single-channel kinetics: they dramatically elevated the open probability (P(O) > 0.8), increased the mean open time and the mean burst duration, reduced the frequency and number of interburst closed states, and eliminated the short burst states. By comparing our results with those obtained for wild-type K(ATP) channels, we conclude that the MgADP sensitivity of the wild-type K(ATP) channel can be described quantitatively by a combination of inhibition at Kir6.2 (measured for wild-type channels in the absence of Mg(2+)) and activation via SUR1 (determined for Kir6.2-G334D/SUR1 channels). However, this is not the case for the effects of MgATP.
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Project description:Brucellosis is a prevalent zoonotic disease and is endemic in the Middle East, South America, and other areas of the world. In this study, complete inventories of putative functional ABC systems of five Brucella species have been compiled and compared. ABC systems of Brucella melitensis 16M, Brucella abortus 9-941, Brucella canis RM6/66, Brucella suis 1330, and Brucella ovis 63/290 were identified and aligned. High numbers of ABC systems, particularly nutrient importers, were found in all Brucella species. However, differences in the total numbers of ABC systems were identified (B. melitensis, 79; B. suis, 72; B. abortus 64; B. canis, 74; B. ovis, 59) as well as specific differences in the functional ABC systems of the Brucella species. Since B. ovis is not known to cause human brucellosis, functional ABC systems absent in the B. ovis genome may represent virulence factors in human brucellosis.
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Project description:The opportunistic yeast pathogen Candida glabrata is recognized for its ability to acquire resistance during prolonged treatment with azole antifungals. Resistance to azoles is largely mediated by the transcription factor PDR1, resulting in the upregulation of ATP-binding cassette (ABC) transporter proteins and drug efflux. Studies in the related yeast Saccharomyces cerevisiae have shown Pdr1p forms a heterodimer with another transcription factor, Stb5p. In C. glabrata the ORF designated CAGL0I02552g has 38.8% amino acid identity with STB5 (YHR178w), and shares an N-terminal Zn2Cys6 binuclear cluster domain and a fungal specific transcriptional factor domain, prompting us to test for homologous function and a possible role in azole resistance. Complementation of deltayhr178w (stb5) with CAGL0I02552g resolved the increased sensitivity to cold, hydrogen peroxide and caffeine of the mutant, for which reason we designated CAGl0I02552g as CgSTB5. Overexpression of CgSTB5 in C. glabrata repressed azole resistance, whereas deletion of CgSTB5 increased resistance, both by a mechanism independent of CgPDR1. Expression analysis found that CgSTB5 shares many of the same transcriptional targets as CgPDR1 but, unlike the later, is a negative regulator of pleiotropic drug resistance, including the ABC transporter genes CDR1,PDH1, and YOR1. The CgPDR1OE (n=5) arrays consisted of five technical repeats with one prepared using reciprocal labeling. The Cgstb5delta (n=4) and CgSTB5OE (n=4) arrays consisted of four technical repeats each with one prepared using reciprocal labeling.
2013-03-11 | E-GEOD-37071 | biostudies-arrayexpress
Project description:P2X receptors are trimeric ATP-activated ion channels permeable to Na+, K+ and Ca2+. The seven P2X receptor subtypes are implicated in physiological processes that include modulation of synaptic transmission, contraction of smooth muscle, secretion of chemical transmitters and regulation of immune responses. Despite the importance of P2X receptors in cellular physiology, the three-dimensional composition of the ATP-binding site, the structural mechanism of ATP-dependent ion channel gating and the architecture of the open ion channel pore are unknown. Here we report the crystal structure of the zebrafish P2X4 receptor in complex with ATP and a new structure of the apo receptor. The agonist-bound structure reveals a previously unseen ATP-binding motif and an open ion channel pore. ATP binding induces cleft closure of the nucleotide-binding pocket, flexing of the lower body ?-sheet and a radial expansion of the extracellular vestibule. The structural widening of the extracellular vestibule is directly coupled to the opening of the ion channel pore by way of an iris-like expansion of the transmembrane helices. The structural delineation of the ATP-binding site and the ion channel pore, together with the conformational changes associated with ion channel gating, will stimulate development of new pharmacological agents.
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Project description:The opportunistic yeast pathogen Candida glabrata is recognized for its ability to acquire resistance during prolonged treatment with azole antifungals. Resistance to azoles is largely mediated by the transcription factor PDR1, resulting in the upregulation of ATP-binding cassette (ABC) transporter proteins and drug efflux. Studies in the related yeast Saccharomyces cerevisiae have shown Pdr1p forms a heterodimer with another transcription factor, Stb5p. In C. glabrata the ORF designated CAGL0I02552g has 38.8% amino acid identity with STB5 (YHR178w), and shares an N-terminal Zn2Cys6 binuclear cluster domain and a fungal specific transcriptional factor domain, prompting us to test for homologous function and a possible role in azole resistance. Complementation of deltayhr178w (stb5) with CAGL0I02552g resolved the increased sensitivity to cold, hydrogen peroxide and caffeine of the mutant, for which reason we designated CAGl0I02552g as CgSTB5. Overexpression of CgSTB5 in C. glabrata repressed azole resistance, whereas deletion of CgSTB5 increased resistance, both by a mechanism independent of CgPDR1. Expression analysis found that CgSTB5 shares many of the same transcriptional targets as CgPDR1 but, unlike the later, is a negative regulator of pleiotropic drug resistance, including the ABC transporter genes CDR1,PDH1, and YOR1.
2013-03-11 | GSE37071 | GEO
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Project description:The cystic fibrosis transmembrane conductance regulator (CFTR) is a member of the ATP-binding cassette (ABC) transporter superfamily, an ancient family of proteins found in all phyla. In nearly all cases, ABC proteins are transporters that couple the hydrolysis of ATP to the transmembrane movement of substrate via an alternating access mechanism. In contrast, CFTR is best known for its activity as an ATP-dependent chloride channel. We asked why CFTR, which shares the domain architecture of ABC proteins that function as transporters, exhibits functional divergence. We compared CFTR protein sequences to those of other ABC transporters, which identified the ABCC4 proteins as the closest mammalian paralogs, and used statistical analysis of the CFTR-ABCC4 multiple sequence alignment to identify the specific domains and residues most likely to be involved in the evolutionary transition from transporter to channel activity. Among the residues identified as being involved in CFTR functional divergence, by virtue of being both CFTR-specific and conserved among all CFTR orthologs, was R352 in the sixth transmembrane helix (TM6). Patch-clamp experiments show that R352 interacts with D993 in TM9 to stabilize the open-channel state; D993 is absolutely conserved between CFTRs and ABCC4s. These data suggest that CFTR channel activity evolved, at least in part, by converting the conformational changes associated with binding and hydrolysis of ATP, as are found in true ABC Transporters, into an open permeation pathway by means of intraprotein interactions that stabilize the open state. This analysis sets the stage for understanding the evolutionary and functional relationships that make CFTR a unique ABC transporter protein.
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