1
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Zhang C, Feng Y, Balutowski A, Miner GE, Rivera-Kohr DA, Hrabak MR, Sullivan KD, Guo A, Calderin JD, Fratti RA. The interdependent transport of yeast vacuole Ca 2+ and H + and the role of phosphatidylinositol 3,5-bisphosphate. J Biol Chem 2022; 298:102672. [PMID: 36334632 PMCID: PMC9706634 DOI: 10.1016/j.jbc.2022.102672] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2022] [Revised: 10/30/2022] [Accepted: 10/31/2022] [Indexed: 11/27/2022] Open
Abstract
Yeast vacuoles are acidified by the v-type H+-ATPase (V-ATPase) that is comprised of the membrane embedded VO complex and the soluble cytoplasmic V1 complex. The assembly of the V1-VO holoenzyme on the vacuole is stabilized in part through interactions between the VO a-subunit ortholog Vph1 and the lipid phosphatidylinositol 3,5-bisphosphate (PI(3,5)P2). PI(3,5)P2 also affects vacuolar Ca2+ release through the channel Yvc1 and uptake through the Ca2+ pump Pmc1. Here, we asked if H+ and Ca2+ transport activities were connected through PI(3,5)P2. We found that overproduction of PI(3,5)P2 by the hyperactive fab1T2250A mutant augmented vacuole acidification, whereas the kinase-inactive fab1EEE mutant attenuated the formation of a H+ gradient. Separately, we tested the effects of excess Ca2+ on vacuole acidification. Adding micromolar Ca2+ blocked vacuole acidification, whereas chelating Ca2+ accelerated acidification. The effect of adding Ca2+ on acidification was eliminated when the Ca2+/H+ antiporter Vcx1 was absent, indicating that the vacuolar H+ gradient can collapse during Ca2+ stress through Vcx1 activity. This, however, was independent of PI(3,5)P2, suggesting that PI(3,5)P2 plays a role in submicromolar Ca2+ flux but not under Ca2+ shock. To see if the link between Ca2+ and H+ transport was bidirectional, we examined Ca2+ transport when vacuole acidification was inhibited. We found that Ca2+ transport was inhibited by halting V-ATPase activity with Bafilomycin or neutralizing vacuolar pH with chloroquine. Together, these data show that Ca2+ transport and V-ATPase efficacy are connected but not necessarily through PI(3,5)P2.
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Affiliation(s)
- Chi Zhang
- Department of Biochemistry, University of Illinois Urbana-Champaign, Urbana, Illinois, USA
| | - Yilin Feng
- Department of Biochemistry, University of Illinois Urbana-Champaign, Urbana, Illinois, USA
| | - Adam Balutowski
- Department of Biochemistry, University of Illinois Urbana-Champaign, Urbana, Illinois, USA
| | - Gregory E Miner
- Department of Biochemistry, University of Illinois Urbana-Champaign, Urbana, Illinois, USA
| | - David A Rivera-Kohr
- Department of Biochemistry, University of Illinois Urbana-Champaign, Urbana, Illinois, USA
| | - Michael R Hrabak
- Department of Biochemistry, University of Illinois Urbana-Champaign, Urbana, Illinois, USA
| | - Katherine D Sullivan
- Department of Biochemistry, University of Illinois Urbana-Champaign, Urbana, Illinois, USA
| | - Annie Guo
- Department of Biochemistry, University of Illinois Urbana-Champaign, Urbana, Illinois, USA
| | - Jorge D Calderin
- Department of Biochemistry, University of Illinois Urbana-Champaign, Urbana, Illinois, USA
| | - Rutilio A Fratti
- Department of Biochemistry, University of Illinois Urbana-Champaign, Urbana, Illinois, USA; Center for Biophysics & Quantitative Biology, University of Illinois Urbana-Champaign, Urbana, Illinois, USA.
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2
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Spolaor S, Rovetta M, Nobile MS, Cazzaniga P, Tisi R, Besozzi D. Modeling Calcium Signaling in S. cerevisiae Highlights the Role and Regulation of the Calmodulin-Calcineurin Pathway in Response to Hypotonic Shock. Front Mol Biosci 2022; 9:856030. [PMID: 35664674 PMCID: PMC9158465 DOI: 10.3389/fmolb.2022.856030] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2022] [Accepted: 04/04/2022] [Indexed: 01/17/2023] Open
Abstract
Calcium homeostasis and signaling processes in Saccharomyces cerevisiae, as well as in any eukaryotic organism, depend on various transporters and channels located on both the plasma and intracellular membranes. The activity of these proteins is regulated by a number of feedback mechanisms that act through the calmodulin-calcineurin pathway. When exposed to hypotonic shock (HTS), yeast cells respond with an increased cytosolic calcium transient, which seems to be conditioned by the opening of stretch-activated channels. To better understand the role of each channel and transporter involved in the generation and recovery of the calcium transient—and of their feedback regulations—we defined and analyzed a mathematical model of the calcium signaling response to HTS in yeast cells. The model was validated by comparing the simulation outcomes with calcium concentration variations before and during the HTS response, which were observed experimentally in both wild-type and mutant strains. Our results show that calcium normally enters the cell through the High Affinity Calcium influx System and mechanosensitive channels. The increase of the plasma membrane tension, caused by HTS, boosts the opening probability of mechanosensitive channels. This event causes a sudden calcium pulse that is rapidly dissipated by the activity of the vacuolar transporter Pmc1. According to model simulations, the role of another vacuolar transporter, Vcx1, is instead marginal, unless calcineurin is inhibited or removed. Our results also suggest that the mechanosensitive channels are subject to a calcium-dependent feedback inhibition, possibly involving calmodulin. Noteworthy, the model predictions are in accordance with literature results concerning some aspects of calcium homeostasis and signaling that were not specifically addressed within the model itself, suggesting that it actually depicts all the main cellular components and interactions that constitute the HTS calcium pathway, and thus can correctly reproduce the shaping of the calcium signature by calmodulin- and calcineurin-dependent complex regulations. The model predictions also allowed to provide an interpretation of different regulatory schemes involved in calcium handling in both wild-type and mutants yeast strains. The model could be easily extended to represent different calcium signals in other eukaryotic cells.
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Affiliation(s)
- Simone Spolaor
- Department of Informatics, Systems and Communication, University of Milano-Bicocca, Milan, Italy
| | - Mattia Rovetta
- Department of Informatics, Systems and Communication, University of Milano-Bicocca, Milan, Italy
| | - Marco S. Nobile
- Department of Environmental Sciences, Informatics and Statistics, Ca’ Foscari University of Venice, Venice, Italy
- Bicocca Bioinformatics, Biostatistics and Bioimaging Centre—B4, Milan, Italy
- SYSBIO/ISBE.IT Centre of Systems Biology, Milan, Italy
| | - Paolo Cazzaniga
- Bicocca Bioinformatics, Biostatistics and Bioimaging Centre—B4, Milan, Italy
- SYSBIO/ISBE.IT Centre of Systems Biology, Milan, Italy
- Department of Human and Social Sciences, University of Bergamo, Bergamo, Italy
| | - Renata Tisi
- Department of Biotechnology and Biosciences, University of Milano-Bicocca, Milan, Italy
- *Correspondence: Renata Tisi, ; Daniela Besozzi,
| | - Daniela Besozzi
- Department of Informatics, Systems and Communication, University of Milano-Bicocca, Milan, Italy
- Bicocca Bioinformatics, Biostatistics and Bioimaging Centre—B4, Milan, Italy
- SYSBIO/ISBE.IT Centre of Systems Biology, Milan, Italy
- *Correspondence: Renata Tisi, ; Daniela Besozzi,
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3
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Miner GE, Sullivan KD, Zhang C, Rivera-Kohr D, Guo A, Hurst LR, Ellis EC, Starr ML, Jones BC, Fratti RA. Phosphatidylinositol 3,5-bisphosphate regulates Ca 2+ transport during yeast vacuolar fusion through the Ca 2+ ATPase Pmc1. Traffic 2021; 21:503-517. [PMID: 32388897 DOI: 10.1111/tra.12736] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2020] [Revised: 05/04/2020] [Accepted: 05/06/2020] [Indexed: 01/02/2023]
Abstract
The transport of Ca2+ across membranes precedes the fusion and fission of various lipid bilayers. Yeast vacuoles under hyperosmotic stress become fragmented through fission events that requires the release of Ca2+ stores through the TRP channel Yvc1. This requires the phosphorylation of phosphatidylinositol-3-phosphate (PI3P) by the PI3P-5-kinase Fab1 to produce transient PI(3,5)P2 pools. Ca2+ is also released during vacuole fusion upon trans-SNARE complex assembly, however, its role remains unclear. The effect of PI(3,5)P2 on Ca2+ flux during fusion was independent of Yvc1. Here, we show that while low levels of PI(3,5)P2 were required for Ca2+ uptake into the vacuole, increased concentrations abolished Ca2+ efflux. This was as shown by the addition of exogenous dioctanoyl PI(3,5)P2 or increased endogenous production of by the hyperactive fab1T2250A mutant. In contrast, the lack of PI(3,5)P2 on vacuoles from the kinase dead fab1EEE mutant showed delayed and decreased Ca2+ uptake. The effects of PI(3,5)P2 were linked to the Ca2+ pump Pmc1, as its deletion rendered vacuoles resistant to the effects of excess PI(3,5)P2 . Experiments with Verapamil inhibited Ca2+ uptake when added at the start of the assay, while adding it after Ca2+ had been taken up resulted in the rapid expulsion of Ca2+ . Vacuoles lacking both Pmc1 and the H+ /Ca2+ exchanger Vcx1 lacked the ability to take up Ca2+ and instead expelled it upon the addition of ATP. Together these data suggest that a balance of efflux and uptake compete during the fusion pathway and that the levels of PI(3,5)P2 can modulate which path predominates.
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Affiliation(s)
- Gregory E Miner
- Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA
| | - Katherine D Sullivan
- Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA
| | - Chi Zhang
- Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA
| | - David Rivera-Kohr
- Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA
| | - Annie Guo
- Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA
| | - Logan R Hurst
- Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA
| | - Ez C Ellis
- Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA
| | - Matthew L Starr
- Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA
| | - Brandon C Jones
- Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA
| | - Rutilio A Fratti
- Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA.,Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA
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4
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Wenzhong L, Hualan L. COVID-19: the CaMKII-like system of S protein drives membrane fusion and induces syncytial multinucleated giant cells. Immunol Res 2021; 69:496-519. [PMID: 34410575 PMCID: PMC8374125 DOI: 10.1007/s12026-021-09224-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2021] [Accepted: 07/24/2021] [Indexed: 02/07/2023]
Abstract
The SARS-CoV-2 S protein on the membrane of infected cells can promote receptor-dependent syncytia formation, relating to extensive tissue damage and lymphocyte elimination. In this case, it is challenging to obtain neutralizing antibodies and prevent them through antibodies effectively. Considering that, in the current study, structural domain search methods are adopted to analyze the SARS-CoV-2 S protein to find the fusion mechanism. The results show that after the EF-hand domain of S protein bound to calcium ions, S2 protein had CaMKII protein activities. Besides, the CaMKII_AD domain of S2 changed S2 conformation, facilitating the formation of HR1-HR2 six-helix bundles. Apart from that, the Ca2+-ATPase of S2 pumped calcium ions from the virus cytoplasm to help membrane fusion, while motor structures of S drove the CaATP_NAI and CaMKII_AD domains to extend to the outside and combined the viral membrane and the cell membrane, thus forming a calcium bridge. Furthermore, the phospholipid-flipping-ATPase released water, triggering lipid mixing and fusion and generating fusion pores. Then, motor structures promoted fusion pore extension, followed by the cytoplasmic contents of the virus being discharged into the cell cytoplasm. After that, the membrane of the virus slid onto the cell membrane along the flowing membrane on the gap of the three CaATP_NAI. At last, the HR1-HR2 hexamer would fall into the cytoplasm or stay on the cell membrane. Therefore, the CaMKII_like system of S protein facilitated membrane fusion for further inducing syncytial multinucleated giant cells.
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Affiliation(s)
- Liu Wenzhong
- grid.412605.40000 0004 1798 1351School of Computer Science and Engineering, Sichuan University of Science & Engineering, Zigong, 643002 China ,grid.413041.30000 0004 1808 3369School of Life Science and Food Engineering, Yibin University, Yibin, 644000 China
| | - Li Hualan
- grid.413041.30000 0004 1808 3369School of Life Science and Food Engineering, Yibin University, Yibin, 644000 China
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5
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Lange M, Peiter E. Calcium Transport Proteins in Fungi: The Phylogenetic Diversity of Their Relevance for Growth, Virulence, and Stress Resistance. Front Microbiol 2020; 10:3100. [PMID: 32047484 PMCID: PMC6997533 DOI: 10.3389/fmicb.2019.03100] [Citation(s) in RCA: 27] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2019] [Accepted: 12/20/2019] [Indexed: 12/26/2022] Open
Abstract
The key players of calcium (Ca2+) homeostasis and Ca2+ signal generation, which are Ca2+ channels, Ca2+/H+ antiporters, and Ca2+-ATPases, are present in all fungi. Their coordinated action maintains a low Ca2+ baseline, allows a fast increase in free Ca2+ concentration upon a stimulus, and terminates this Ca2+ elevation by an exponential decrease – hence forming a Ca2+ signal. In this respect, the Ca2+ signaling machinery is conserved in different fungi. However, does the similarity of the genetic inventory that shapes the Ca2+ peak imply that if “you’ve seen one, you’ve seen them all” in terms of physiological relevance? Individual studies have focused mostly on a single species, and mechanisms elucidated in few model organisms are usually extrapolated to other species. This mini-review focuses on the physiological relevance of the machinery that maintains Ca2+ homeostasis for growth, virulence, and stress responses. It reveals common and divergent functions of homologous proteins in different fungal species. In conclusion, for the physiological role of these Ca2+ transport proteins, “seen one,” in many cases, does not mean: “seen them all.”
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Affiliation(s)
- Mario Lange
- Plant Nutrition Laboratory, Institute of Agricultural and Nutritional Sciences, Faculty of Natural Sciences III, Martin Luther University of Halle-Wittenberg, Halle (Saale), Germany
| | - Edgar Peiter
- Plant Nutrition Laboratory, Institute of Agricultural and Nutritional Sciences, Faculty of Natural Sciences III, Martin Luther University of Halle-Wittenberg, Halle (Saale), Germany
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6
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Abstract
During in vitro homotypic yeast vacuole fusion Ca2+ is transported into and out of the organelle lumen. In vitro, Ca2+ is taken up from the medium by vacuoles upon the addition of ATP. During the docking stage of vacuole fusion Ca2+ is effluxed from the lumen upon the formation of trans-SNARE complexes between vesicles. Here we describe a real-time fluorescence-based assay to monitor the transport of this cation using purified organelles. Extraluminal Ca2+ is detected when the cation binds the low-affinity fluorescent dye Fluo-4 dextran. This allows for the use of a 96-well microtiter plate to be read in a fluorescence plate reader. Thus, in addition to a curve of calibrated Ca2+ standards, up to 91 experimental conditions can be monitored in a single microplate using this method.
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7
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Organelle acidification negatively regulates vacuole membrane fusion in vivo. Sci Rep 2016; 6:29045. [PMID: 27363625 PMCID: PMC4929563 DOI: 10.1038/srep29045] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2016] [Accepted: 06/10/2016] [Indexed: 12/13/2022] Open
Abstract
The V-ATPase is a proton pump consisting of a membrane-integral V0 sector and a peripheral V1 sector, which carries the ATPase activity. In vitro studies of yeast vacuole fusion and evidence from worms, flies, zebrafish and mice suggested that V0 interacts with the SNARE machinery for membrane fusion, that it promotes the induction of hemifusion and that this activity requires physical presence of V0 rather than its proton pump activity. A recent in vivo study in yeast has challenged these interpretations, concluding that fusion required solely lumenal acidification but not the V0 sector itself. Here, we identify the reasons for this discrepancy and reconcile it. We find that acute pharmacological or physiological inhibition of V-ATPase pump activity de-acidifies the vacuole lumen in living yeast cells within minutes. Time-lapse microscopy revealed that de-acidification induces vacuole fusion rather than inhibiting it. Cells expressing mutated V0 subunits that maintain vacuolar acidity were blocked in this fusion. Thus, proton pump activity of the V-ATPase negatively regulates vacuole fusion in vivo. Vacuole fusion in vivo does, however, require physical presence of a fusion-competent V0 sector.
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8
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Abstract
Calcium is an essential cation for a cell. This cation participates in the regulation of numerous processes in either prokaryotes or eukaryotes, from bacteria to humans. Saccharomyces cerevisiae has served as a model organism to understand calcium homeostasis and calcium-dependent signaling in fungi. In this chapter it will be reviewed known and predicted transport mechanisms that mediate calcium homeostasis in the yeast. How and when calcium enters the cell, how and where it is stored, when is reutilized, and finally secreted to the environment to close the cycle. As a second messenger, maintenance of a controlled free intracellular calcium concentration is important for mediating transcriptional regulation. Many environmental stimuli modify the concentration of cytoplasmic free calcium generating the "calcium signal". This is sensed and transduced through the calmodulin/calcineurin pathway to a transcription factor, named calcineurin-responsive zinc finger, CRZ, also known as "crazy", to mediate transcriptional regulation of a large number of genes of diverse pathways including a negative feedback regulation of the calcium homeostasis system.
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Affiliation(s)
- Eduardo A Espeso
- Department of Cellular and Molecular Biology, Centro de Investigaciones Biológicas, CSIC, Ramiro de Maeztu, 9, 28040, Madrid, Spain.
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9
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Expression of NYV1 encoding the negative regulator of Pmc1 is repressed by two transcriptional repressors, Nrg1 and Mig1. FEBS Lett 2014; 588:3195-201. [PMID: 25017437 DOI: 10.1016/j.febslet.2014.06.062] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2014] [Revised: 06/25/2014] [Accepted: 06/30/2014] [Indexed: 12/26/2022]
Abstract
ESCRT components function to form multivesicular bodies for sorting of proteins destined to the yeast vacuole. The calcium hypersensitivity of ESCRT mutants is mainly due to repressed expression of PMR1 through the Rim101/Nrg1 pathway in budding yeast. Here, we show that overexpression of PMC1 and its negative regulator gene NYV1 suppresses and increases calcium hypersensitivity of ESCRT mutants, respectively. Consistently, deletion of NYV1 suppresses their calcium hypersensitivity. Expression of NYV1 is dramatically reduced in ESCRT mutants. Promoter analysis demonstrates that both Nrg1 and Mig1 repress NYV1 expression. Deletion of ESCRTs increases Nrg1 binding, but not Mig1-binding, to the NYV1 promoter. Deletion of MIG1 increases calcium sensitivity of ESCRT mutants due to derepression of NYV1 expression.
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10
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Sasser TL, Fratti RA. Class C ABC transporters and Saccharomyces cerevisiae vacuole fusion. CELLULAR LOGISTICS 2014; 4:e943588. [PMID: 25610719 DOI: 10.4161/21592780.2014.943588] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/05/2014] [Accepted: 06/18/2014] [Indexed: 01/05/2023]
Abstract
Membrane fusion is carried out by core machinery that is conserved throughout eukaryotes. This is comprised of Rab GTPases and their effectors, and SNARE proteins, which together are sufficient to drive the fusion of reconstituted proteoliposomes. However, an outer layer of factors that are specific to individual trafficking pathways in vivo regulates the spatial and temporal occurrence of fusion. The homotypic fusion of Saccharomyces cerevisiae vacuolar lysosomes utilizes a growing set of factors to regulate the fusion machinery that include members of the ATP binding cassette (ABC) transporter family. Yeast vacuoles have five class C ABC transporters that are known to transport a variety of toxins into the vacuole lumen as part of detoxifying the cell. We have found that ABCC transporters can also regulate vacuole fusion through novel mechanisms. For instance Ybt1 serves as negative regulator of fusion through its effects on vacuolar Ca2+ homeostasis. Additional studies showed that Ycf1 acts as a positive regulator by affecting the efficient recruitment of the SNARE Vam7. Finally, we discuss the potential interface between the translocation of lipids across the membrane bilayer, also known as lipid flipping, and the efficiency of fusion.
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Key Words
- ABC, ATP binding cassette
- Bpt1
- Ca2+ homeostasis
- DAG, diacylglycerol
- HOPS, homotypic fusion and vacuole protein sorting complex
- MDR, multidrug resistance
- MSD, membrane spanning domain
- NBD, nucleotide binding domain
- Nft1
- PA, phosphatidic acid
- PC, phosphatidylcholine
- PE, phosphatidylethanolamine
- PI(3, 5)P2, phosphatidylinositol 3, 5-bisphosphate
- PI, phosphatidylinositol
- PI3P
- PI3P, phosphatidylinositol 3-phosphate
- PS, phosphatidylserine
- PX, phox homology
- SNARE
- SNARE, soluble N-ethylmaleimide-sensitive factor attachment protein receptors
- Vam7
- Vmr1
- Ybt1
- Ycf1
- lipid flipping
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Affiliation(s)
- Terry L Sasser
- Department of Biochemistry; University of Illinois at Urbana-Champaign ; Urbana, IL USA
| | - Rutilio A Fratti
- Department of Biochemistry; University of Illinois at Urbana-Champaign ; Urbana, IL USA
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11
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The yeast vacuolar ABC transporter Ybt1p regulates membrane fusion through Ca2+ transport modulation. Biochem J 2013; 448:365-72. [PMID: 22970809 DOI: 10.1042/bj20120847] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Ybt1p is a class C ABC transporter (ATP-binding cassette transporter) that is localized to the vacuole of Saccharomyces cerevisiae. Although Ybt1p was originally identified as a bile acid transporter, it has also been found to function in other capacities, including the translocation of phosphatidylcholine to the vacuole lumen, and the regulation of Ca2+ homoeostasis. In the present study we found that deletion of YBT1 enhanced in vitro homotypic vacuole fusion by up to 50% relative to wild-type vacuoles. The increased vacuole fusion was not due to aberrant protein sorting of SNAREs (soluble N-ethylmaleimide-sensitive factor-attachment protein receptors) or recruitment of factors from the cytosol such as Ypt7p and the HOPS (homotypic fusion and vacuole protein sorting) tethering complex. In addition, ybt1Δ vacuoles displayed no observable differences in the formation of SNARE complexes, interactions between SNAREs and HOPS, or formation of vertex microdomains. However, the absence of Ybt1p caused significant changes in Ca2+ transport during fusion. One difference was the prolonged Ca2+ influx exhibited by ybt1Δ vacuoles at the start of the fusion reaction. We also observed a striking delay in SNARE-dependent Ca2+ efflux. As vacuole fusion can be inhibited by high Ca2+ concentrations, we suggest that the delayed efflux in ybt1Δ vacuoles leads to the enhanced SNARE function.
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12
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Mielniczki-Pereira AA, Hahn ABB, Bonatto D, Riger CJ, Eleutherio ECA, Henriques JAP. New insights into the Ca2+-ATPases that contribute to cadmium tolerance in yeast. Toxicol Lett 2011; 207:104-11. [PMID: 21911041 DOI: 10.1016/j.toxlet.2011.08.023] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2011] [Revised: 08/29/2011] [Accepted: 08/29/2011] [Indexed: 01/16/2023]
Abstract
Cadmium (Cd(2+)) is a toxic heavy metal which triggers several toxic effects in eukaryotes, including neurotoxicity and impaired calcium metabolism. In the model organism Saccharomyces cerevisiae, the best characterized pathway for Cd(2+) detoxification involves conjugation with glutathione (GSH) and subsequent transport to vacuoles by Ycf1p, an ATPase homologous to human MRP1 (Multidrug resistance associated protein 1). However, Cd(2+) tolerance also can be mediated by Pmr1p, a Ca(2+) pump located in the Golgi membrane, possibly through to the secretory pathway. Herein, we showed that inactivation of the PMR1 gene, alone or simultaneously with YCF1, delayed initial Cd(2+) capture compared to wild-type (WT) cells. In addition, Cd(2+) treatment altered the expression profile of yeast internal Ca(2+) transporters; specifically, PMC1 gene expression is induced substantially by the metal in WT cells, and this induction is stronger in mutants lacking YCF1. Taken together, these results indicate that, in addition to Pmr1p, the vacuolar Ca(2+)-ATPase Pmc1p also helps yeast cells cope with Cd(2+) toxicity. We propose a model where Pmc1p and Pmr1p Ca(2+)-ATPase function in cooperation with Ycf1p to promote Cd(2+) detoxification.
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13
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Pittman JK. Vacuolar Ca(2+) uptake. Cell Calcium 2011; 50:139-46. [PMID: 21310481 DOI: 10.1016/j.ceca.2011.01.004] [Citation(s) in RCA: 93] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2010] [Revised: 12/31/2010] [Accepted: 01/03/2011] [Indexed: 12/22/2022]
Abstract
Calcium transporters that mediate the removal of Ca(2+) from the cytosol and into internal stores provide a critical role in regulating Ca(2+) signals following stimulus induction and in preventing calcium toxicity. The vacuole is a major calcium store in many organisms, particularly plants and fungi. Two main pathways facilitate the accumulation of Ca(2+) into vacuoles, Ca(2+)-ATPases and Ca(2+)/H(+) exchangers. Here I review the biochemical and regulatory features of these transporters that have been characterised in yeast and plants. These Ca(2+) transport mechanisms are compared with those being identified from other vacuolated organisms including algae and protozoa. Studies suggest that Ca(2+) uptake into vacuoles and other related acidic Ca(2+) stores occurs by conserved mechanisms which developed early in evolution.
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Affiliation(s)
- Jon K Pittman
- Faculty of Life Sciences, University of Manchester, Michael Smith Building, Oxford Road, Manchester M13 9PT, UK.
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14
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Tang F, Liu W. An age-dependent feedback control model of calcium dynamics in yeast cells. J Math Biol 2009; 60:849-79. [DOI: 10.1007/s00285-009-0289-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2008] [Revised: 07/24/2009] [Indexed: 12/12/2022]
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15
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Cui J, Kaandorp JA, Ositelu OO, Beaudry V, Knight A, Nanfack YF, Cunningham KW. Simulating calcium influx and free calcium concentrations in yeast. Cell Calcium 2008; 45:123-32. [PMID: 18783827 DOI: 10.1016/j.ceca.2008.07.005] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2007] [Revised: 07/01/2008] [Accepted: 07/21/2008] [Indexed: 11/26/2022]
Abstract
Yeast can proliferate in environments containing very high Ca(2+) primarily due to the activity of vacuolar Ca(2+) transporters Pmc1 and Vcx1. Yeast mutants lacking these transporters fail to grow in high Ca(2+) environments, but growth can be restored by small increases in environmental Mg(2+). Low extracellular Mg(2+) appeared to competitively inhibit novel Ca(2+) influx pathways and to diminish the concentration of free Ca(2+) in the cytoplasm, as judged from the luminescence of the photoprotein aequorin. These Mg(2+)-sensitive Ca(2+) influx pathways persisted in yvc1 cch1 double mutants. Based on mathematical models of the aequorin luminescence traces, we propose the existence in yeast of at least two Ca(2+) transporters that undergo rapid feedback inhibition in response to elevated cytosolic free Ca(2+) concentration. Finally, we show that Vcx1 helps return cytosolic Ca(2+) toward resting levels after shock with high extracellular Ca(2+) much more effectively than Pmc1 and that calcineurin, a protein phosphatase regulator of Vcx1 and Pmc1, had no detectable effects on these factors within the first few minutes of its activation. Therefore, computational modeling of Ca(2+) transport and signaling in yeast can provide important insights into the dynamics of this complex system.
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Affiliation(s)
- Jiangjun Cui
- Section Computational Science, Faculty of Science, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands.
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Sokolovski S, Hills A, Gay RA, Blatt MR. Functional interaction of the SNARE protein NtSyp121 in Ca2+ channel gating, Ca2+ transients and ABA signalling of stomatal guard cells. MOLECULAR PLANT 2008; 1:347-58. [PMID: 19825544 DOI: 10.1093/mp/ssm029] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
There is now growing evidence that membrane vesicle trafficking proteins, especially of the superfamily of SNAREs, are critical for cellular signalling in plants. Work from this laboratory first demonstrated that a soluble, inhibitory (dominant-negative) fragment of the SNARE NtSyp121 blocked K+ and Cl- channel responses to the stress-related hormone abscisic acid (ABA), but left open a question about functional impacts on signal intermediates, especially on Ca2+-mediated signalling events. Here, we report one mode of action for the SNARE mediated directly through alterations in Ca2+ channel gating and its consequent effects on cytosolic-free [Ca2+] ([Ca2+]i) elevation. We find that expressing the same inhibitory fragment of NtSyp121 blocks ABA-evoked stomatal closure, but only partially suppresses stomatal closure in the presence of the NO donor, SNAP, which promotes [Ca2+]i elevation independently of the plasma membrane Ca2+ channels. Consistent with these observations, Ca2+ channel gating at the plasma membrane is altered by the SNARE fragment in a manner effective in reducing the potential for triggering a rise in [Ca2+]i, and we show directly that its expression in vivo leads to a pronounced suppression of evoked [Ca2+]i transients. These observations offer primary evidence for the functional coupling of the SNARE with Ca2+ channels at the plant cell plasma membrane and, because [Ca2+]i plays a key role in the control of K+ and Cl- channel currents in guard cells, they underscore an important mechanism for SNARE integration with ion channel regulation during stomatal closure.
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Affiliation(s)
- Sergei Sokolovski
- Laboratory of Plant Physiology and Biophysics, IBLS-Plant Sciences, University of Glasgow, Glasgow G12 8QQ, UK
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Cui J, Kaandorp JA. Mathematical modeling of calcium homeostasis in yeast cells. Cell Calcium 2006; 39:337-48. [PMID: 16445978 DOI: 10.1016/j.ceca.2005.12.001] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2004] [Revised: 12/01/2005] [Accepted: 12/08/2005] [Indexed: 11/21/2022]
Abstract
In this study, based on currently available experimental observations on protein level, we constructed a mathematical model to describe calcium homeostasis in normally growing yeast cells (Saccharomyces cerevisiae). Simulation results show that tightly controlled low cytosolic calcium ion level can be a natural result under the general mechanism of gene expression feedback control. The calmodulin (a sensor protein) behavior in our model cell agrees well with relevant observations in real cells. Moreover, our model can qualitatively reproduce the experimentally observed response curve of real yeast cell responding to step-like disturbance in extracellular calcium ion concentration. Further investigations show that the feedback control mechanism in our model is as robust as it is in real cells.
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Affiliation(s)
- Jiangjun Cui
- Section Computational Science, Faculty of Science, University of Amsterdam, The Netherlands
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Abstract
Ca2+ transients trigger many SNARE-dependent membrane fusion events. The homotypic fusion of yeast vacuoles occurs after a release of lumenal Ca2+. Here, we show that trans-SNARE interactions promote the release of Ca2+ from the vacuole lumen. Ypt7p–GTP, the Sec1p/Munc18-protein Vps33p, and Rho GTPases, all of which function during docking, are required for Ca2+ release. Inhibitors of SNARE function prevent Ca2+ release. Recombinant Vam7p, a soluble Q-SNARE, stimulates Ca2+ release. Vacuoles lacking either of two complementary SNAREs, Vam3p or Nyv1p, fail to release Ca2+ upon tethering. Mixing these two vacuole populations together allows Vam3p and Nyv1p to interact in trans and rescues Ca2+ release. Sec17/18p promote sustained Ca2+ release by recycling SNAREs (and perhaps other limiting factors), but are not required at the release step itself. We conclude that trans-SNARE assembly events during docking promote Ca2+ release from the vacuole lumen.
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Affiliation(s)
- Alexey J Merz
- Dept. of Biochemistry, 7200 Vail Bldg., Dartmouth Medical School, Hanover, NH 03755-3844, USA
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