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Puri N, Fernandez AJ, O'Shea Murray VL, McMillan S, Keck JL, Berger JM. The molecular coupling between substrate recognition and ATP turnover in a AAA+ hexameric helicase loader. eLife 2021; 10:64232. [PMID: 34036936 PMCID: PMC8213410 DOI: 10.7554/elife.64232] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2020] [Accepted: 05/25/2021] [Indexed: 11/16/2022] Open
Abstract
In many bacteria and eukaryotes, replication fork establishment requires the controlled loading of hexameric, ring-shaped helicases around DNA by AAA+(ATPases Associated with various cellular Activities) ATPases. How loading factors use ATP to control helicase deposition is poorly understood. Here, we dissect how specific ATPase elements of Escherichia coli DnaC, an archetypal loader for the bacterial DnaB helicase, play distinct roles in helicase loading and the activation of DNA unwinding. We have identified a new element, the arginine-coupler, which regulates the switch-like behavior of DnaC to prevent futile ATPase cycling and maintains loader responsiveness to replication restart systems. Our data help explain how the ATPase cycle of a AAA+-family helicase loader is channeled into productive action on its target; comparative studies indicate that elements analogous to the Arg-coupler are present in related, switch-like AAA+ proteins that control replicative helicase loading in eukaryotes, as well as in polymerase clamp loading and certain classes of DNA transposases.
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Affiliation(s)
- Neha Puri
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins School of Medicine, Baltimore, United States
| | - Amy J Fernandez
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins School of Medicine, Baltimore, United States
| | - Valerie L O'Shea Murray
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins School of Medicine, Baltimore, United States.,Saul Ewing Arnstein & Lehr, LLP, Centre Square West, Philadelphia, United States
| | - Sarah McMillan
- Department of Biomolecular Chemistry, University of Wisconsin School of Medicine and Public Health, Madison, United States
| | - James L Keck
- Department of Biomolecular Chemistry, University of Wisconsin School of Medicine and Public Health, Madison, United States
| | - James M Berger
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins School of Medicine, Baltimore, United States
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2
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Reubold TF, Eschenburg S. A molecular view on signal transduction by the apoptosome. Cell Signal 2012; 24:1420-5. [PMID: 22446004 DOI: 10.1016/j.cellsig.2012.03.007] [Citation(s) in RCA: 115] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2012] [Accepted: 03/05/2012] [Indexed: 12/22/2022]
Abstract
Apoptosomes are signaling platforms that initiate the dismantling of a cell during apoptosis. In mammals, assembly of the apoptosome is the pivotal point in the mitochondrial pathway of apoptosis, and is prompted by binding of cytochrome c to the apoptotic protease-activating factor 1 (Apaf-1) in the presence of ATP. The resulting wheel-like heptamer of seven molecules Apaf-1 and seven molecules cytochrome c binds and activates the initiator caspase-9, which in turn ignites the downstream caspase cascade. In this review we discuss the molecular determinants for the formation of the mammalian apoptosome and caspase activation and describe the related signaling platforms in flies and nematodes.
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Affiliation(s)
- Thomas F Reubold
- Institute for Biophysical Chemistry, Hannover Medical School, Hannover, Germany
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3
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Requirements for the catalytic cycle of the N-ethylmaleimide-Sensitive Factor (NSF). BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2011; 1823:159-71. [PMID: 21689688 DOI: 10.1016/j.bbamcr.2011.06.003] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/23/2011] [Revised: 05/23/2011] [Accepted: 06/06/2011] [Indexed: 12/23/2022]
Abstract
The N-ethylmaleimide-Sensitive Factor (NSF) was one of the initial members of the ATPases Associated with various cellular Activities Plus (AAA(+)) family. In this review, we discuss what is known about the mechanism of NSF action and how that relates to the mechanisms of other AAA(+) proteins. Like other family members, NSF binds to a protein complex (i.e., SNAP-SNARE complex) and utilizes ATP hydrolysis to affect the conformations of that complex. SNAP-SNARE complex disassembly is essential for SNARE recycling and sustained membrane trafficking. NSF is a homo-hexamer; each protomer is composed of an N-terminal domain, NSF-N, and two adjacent AAA-domains, NSF-D1 and NSF-D2. Mutagenesis analysis has established specific roles for many of the structural elements of NSF-D1, the catalytic ATPase domain, and NSF-N, the SNAP-SNARE binding domain. Hydrodynamic analysis of NSF, labeled with (Ni(2+)-NTA)(2)-Cy3, detected conformational differences in NSF, in which the ATP-bound conformation appears more compact than the ADP-bound form. This indicates that NSF undergoes significant conformational changes as it progresses through its ATP-hydrolysis cycle. Incorporating these data, we propose a sequential mechanism by which NSF uses NSF-N and NSF-D1 to disassemble SNAP-SNARE complexes. We also illustrate how analytical centrifugation might be used to study other AAA(+) proteins.
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4
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Page AN, George NP, Marceau AH, Cox MM, Keck JL. Structure and biochemical activities of Escherichia coli MgsA. J Biol Chem 2011; 286:12075-85. [PMID: 21297161 PMCID: PMC3069411 DOI: 10.1074/jbc.m110.210187] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2010] [Revised: 01/14/2011] [Indexed: 11/06/2022] Open
Abstract
Bacterial "maintenance of genome stability protein A" (MgsA) and related eukaryotic enzymes play important roles in cellular responses to stalled DNA replication processes. Sequence information identifies MgsA enzymes as members of the clamp loader clade of AAA+ proteins, but structural information defining the family has been limited. Here, the x-ray crystal structure of Escherichia coli MgsA is described, revealing a homotetrameric arrangement for the protein that distinguishes it from other clamp loader clade AAA+ proteins. Each MgsA protomer is composed of three elements as follows: ATP-binding and helical lid domains (conserved among AAA+ proteins) and a tetramerization domain. Although the tetramerization domains bury the greatest amount of surface area in the MgsA oligomer, each of the domains participates in oligomerization to form a highly intertwined quaternary structure. Phosphate is bound at each AAA+ ATP-binding site, but the active sites do not appear to be in a catalytically competent conformation due to displacement of Arg finger residues. E. coli MgsA is also shown to form a complex with the single-stranded DNA-binding protein through co-purification and biochemical studies. MgsA DNA-dependent ATPase activity is inhibited by single-stranded DNA-binding protein. Together, these structural and biochemical observations provide insights into the mechanisms of MgsA family AAA+ proteins.
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Affiliation(s)
- Asher N. Page
- From the Department of Biochemistry, University of Wisconsin and
| | - Nicholas P. George
- the Department of Biomolecular Chemistry, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin 53706
| | - Aimee H. Marceau
- the Department of Biomolecular Chemistry, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin 53706
| | - Michael M. Cox
- From the Department of Biochemistry, University of Wisconsin and
| | - James L. Keck
- the Department of Biomolecular Chemistry, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin 53706
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5
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Mühlbach H, Mohr CA, Ruzsics Z, Koszinowski UH. Dominant-negative proteins in herpesviruses - from assigning gene function to intracellular immunization. Viruses 2009; 1:420-40. [PMID: 21994555 PMCID: PMC3185506 DOI: 10.3390/v1030420] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2009] [Revised: 10/19/2009] [Accepted: 10/19/2009] [Indexed: 11/17/2022] Open
Abstract
Investigating and assigning gene functions of herpesviruses is a process, which profits from consistent technical innovation. Cloning of bacterial artificial chromosomes encoding herpesvirus genomes permits nearly unlimited possibilities in the construction of genetically modified viruses. Targeted or randomized screening approaches allow rapid identification of essential viral proteins. Nevertheless, mapping of essential genes reveals only limited insight into function. The usage of dominant-negative (DN) proteins has been the tool of choice to dissect functions of proteins during the viral life cycle. DN proteins also facilitate the analysis of host-virus interactions. Finally, DNs serve as starting-point for design of new antiviral strategies.
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Affiliation(s)
| | | | - Zsolt Ruzsics
- Max-von-Pettenkofer Institut, LMU, Feodor-Lynenstr. 25, 81377 Munich, Germany; E-Mails: (H.M.); (C.A.M.); (Z.R.)
| | - Ulrich H. Koszinowski
- Max-von-Pettenkofer Institut, LMU, Feodor-Lynenstr. 25, 81377 Munich, Germany; E-Mails: (H.M.); (C.A.M.); (Z.R.)
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6
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Zhao C, Matveeva EA, Ren Q, Whiteheart SW. Dissecting the N-ethylmaleimide-sensitive factor: required elements of the N and D1 domains. J Biol Chem 2009; 285:761-72. [PMID: 19887446 DOI: 10.1074/jbc.m109.056739] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
N-Ethylmaleimide-sensitive factor (NSF) is a homo-hexameric member of the AAA(+) (ATPases associated with various cellular activities plus) family. It plays an essential role in most intracellular membrane trafficking through its binding to and disassembly of soluble NSF attachment protein (SNAP) receptor (SNARE) complexes. Each NSF protomer contains an N-terminal domain (NSF-N) and two AAA domains, a catalytic NSF-D1 and a structural NSF-D2. This study presents detailed mutagenesis analyses of NSF-N and NSF-D1, dissecting their roles in ATP hydrolysis, SNAP.SNARE binding, and complex disassembly. Our results show that a positively charged surface on NSF-N, bounded by Arg(67) and Lys(105), and the conserved residues in the central pore of NSF-D1 (Tyr(296) and Gly(298)) are involved in SNAP.SNARE binding but not basal ATP hydrolysis. Mutagenesis of Sensor 1 (Thr(373)-Arg(375)), Sensor 2 (Glu(440)-Glu(442)), and Arginine Fingers (Arg(385) and Arg(388)) in NSF-D1 shows that each region plays a discrete role. Sensor 1 is important for basal ATPase activity and nucleotide binding. Sensor 2 plays a role in ATP- and SNAP-dependent SNARE complex binding and disassembly but does so in cis and not through inter-protomer interactions. Arginine Fingers are important for SNAP.SNARE complex-stimulated ATPase activity and complex disassembly. Mutants at these residues have a dominant-negative phenotype in cells, suggesting that Arginine Fingers function in trans via inter-protomer interactions. Taken together, these data establish functional roles for many of the structural elements of the N domain and of the D1 ATP-binding site of NSF.
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Affiliation(s)
- Chunxia Zhao
- Department of Molecular and Cellular Biochemistry, University of Kentucky Medical Center, Lexington, Kentucky 40536-0509, USA
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7
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Zhao C, Slevin JT, Whiteheart SW. Cellular functions of NSF: not just SNAPs and SNAREs. FEBS Lett 2007; 581:2140-9. [PMID: 17397838 PMCID: PMC1948069 DOI: 10.1016/j.febslet.2007.03.032] [Citation(s) in RCA: 89] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2007] [Accepted: 03/07/2007] [Indexed: 12/26/2022]
Abstract
N-ethylmaleimide sensitive factor (NSF) is an ATPases associated with various cellular activities protein (AAA), broadly required for intracellular membrane fusion. NSF functions as a SNAP receptor (SNARE) chaperone which binds, through soluble NSF attachment proteins (SNAPs), to SNARE complexes and utilizes the energy of ATP hydrolysis to disassemble them thus facilitating SNARE recycling. While this is a major function of NSF, it does seem to interact with other proteins, such as the AMPA receptor subunit, GluR2, and beta2-AR and is thought to affect their trafficking patterns. New data suggest that NSF may be regulated by transient post-translational modifications such as phosphorylation and nitrosylation. These new aspects of NSF function as well as its role in SNARE complex dynamics will be discussed.
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Affiliation(s)
- Chunxia Zhao
- Departmental of Molecular and Cellular Biochemistry, University of Kentucky College of Medicine, Lexington, KY, USA
| | - John T. Slevin
- Neurology Service, Department of Veterans Affairs Medical Center, Departments of Neurology and Molecular and Biomedical Pharmacology, University of Kentucky Medical Center, Lexington, KY, USA
| | - Sidney W. Whiteheart
- Departmental of Molecular and Cellular Biochemistry, University of Kentucky College of Medicine, Lexington, KY, USA
- *Corresponding author. 741 South Limestone, BBSRB B261, Lexington, KY 40536, USA. Phone: 1-859-257-4882. Fax: 1-859-257-2283. E-mail address:
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8
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Abstract
The AAA+ (ATPases associated with various cellular activities) family is a large and functionally diverse group of enzymes that are able to induce conformational changes in a wide range of substrate proteins. The family's defining feature is a structurally conserved ATPase domain that assembles into oligomeric rings and undergoes conformational changes during cycles of nucleotide binding and hydrolysis. Here, we review the structural organization of AAA+ proteins, the conformational changes they undergo, the range of different reactions they catalyse, and the diseases associated with their dysfunction.
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Affiliation(s)
- Phyllis I Hanson
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
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9
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Dietrich LEP, LaGrassa TJ, Rohde J, Cristodero M, Meiringer CTA, Ungermann C. ATP-independent control of Vac8 palmitoylation by a SNARE subcomplex on yeast vacuoles. J Biol Chem 2005; 280:15348-55. [PMID: 15701652 DOI: 10.1074/jbc.m410582200] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Yeast vacuole fusion requires palmitoylated Vac8. We previously showed that Vac8 acylation occurs early in the fusion reaction, is blocked by antibodies against Sec18 (yeast N-ethylmaleimide-sensitive fusion protein (NSF)), and is mediated by the R-SNARE Ykt6. Here we analyzed the regulation of this reaction on purified vacuoles. We show that Vac8 acylation is restricted to a narrow time window, is independent of ATP hydrolysis by Sec18, and is stimulated by the ion chelator EDTA. Analysis of vacuole protein complexes indicated that Ykt6 is part of a complex distinct from the second R-SNARE, Nyv1. We speculate that during vacuole fusion, Nyv1 is the classical R-SNARE, whereas the Ykt6-containing complex has a novel function in Vac8 palmitoylation.
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Affiliation(s)
- Lars E P Dietrich
- Biochemie-Zentrum der Universität Heidelberg, Im Neuenheimer Feld 328, 69120 Heidelberg, Germany
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10
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Zhang X, Stoffels K, Wurzbacher S, Schoofs G, Pfeifer G, Banerjee T, Parret AHA, Baumeister W, De Mot R, Zwickl P. The N-terminal coiled coil of the Rhodococcus erythropolis ARC AAA ATPase is neither necessary for oligomerization nor nucleotide hydrolysis. J Struct Biol 2004; 146:155-65. [PMID: 15037247 DOI: 10.1016/j.jsb.2003.10.020] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2003] [Revised: 10/17/2003] [Indexed: 11/18/2022]
Abstract
Deletion mutants of the Rhodococcus erythropolis ARC AAA ATPase were generated and characterized by biochemical analysis and electron microscopy. Based on sequence comparisons the ARC protein was divided into three consecutive regions, the N-terminal coiled coil, the central ARC-specific inter domain and the C-terminal AAA domain. When the ARC AAA domain was expressed separately it formed aggregates of undefined structure. However, when the AAA domain was expressed in conjunction with the preceeding inter domain, but without the N-terminal coiled coil, high-molecular weight-complexes were formed (ARC-DeltaCC) which showed an N-ethylmaleimide-sensitive ATPase activity. In 2D crystallization experiments the ARC-DeltaCC particles yielded crystals nearly identical to those formed by the wild-type ARC complexes. Thus, the N-terminal coiled coil, which was proposed to have a role in the assembly of and/or interaction between the eukaryotic AAA ATPases in the 26S proteasome, is neither essential for assembly nor for ATP hydrolysis of the ARC ATPase. The N-terminal domain of related AAA ATPases mediates the interaction with substrates or co-factors, suggesting a regulatory function for the N-terminal coiled coil of the ARC ATPase. Surprisingly, the mutant ARC protein ARC-DeltaAAA consisting of the N-terminal coiled coil and the central inter domain, but deleted for the C-terminal AAA domain, was shown to form a dodecameric complex with sixfold symmetry. This suggests an important role of the inter domain for the ordered assembly of the ARC ATPase.
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Affiliation(s)
- Xujia Zhang
- Max-Planck-Institut für Biochemie, Am Klopferspitz 18a, D-82152 Martinsried, Germany
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11
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Hattendorf DA, Lindquist SL. Cooperative kinetics of both Hsp104 ATPase domains and interdomain communication revealed by AAA sensor-1 mutants. EMBO J 2002; 21:12-21. [PMID: 11782421 PMCID: PMC125804 DOI: 10.1093/emboj/21.1.12] [Citation(s) in RCA: 148] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
AAA proteins share a conserved active site for ATP hydrolysis and regulate many cellular processes. AAA proteins are oligomeric and often have multiple ATPase domains per monomer, which is suggestive of complex allosteric kinetics of ATP hydrolysis. Here, using wild-type Hsp104 in the hexameric state, we demonstrate that its two AAA modules (NBD1 and NBD2) have very different catalytic activities, but each displays cooperative kinetics of hydrolysis. Using mutations in the AAA sensor-1 motif of NBD1 and NBD2 that reduce the rate of ATP hydrolysis without affecting nucleotide binding, we also examine the consequences of keeping each site in the ATP-bound state. In vitro, reducing k(cat) at NBD2 significantly alters the steady-state kinetic behavior of NBD1. Thus, Hsp104 exhibits allosteric communication between the two sites in addition to homotypic cooperativity at both NBD1 and NBD2. In vivo, each sensor-1 mutation causes a loss-of-function phenotype in two assays of Hsp104 function (thermotolerance and yeast prion propagation), demonstrating the importance of ATP hydrolysis as distinct from ATP binding at each site for Hsp104 function.
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Affiliation(s)
- Douglas A. Hattendorf
- Department of Biochemistry and Molecular Biology and Department of Molecular Genetics and Cell Biology and Howard Hughes Medical Institute, the University of Chicago, Chicago, IL 60637, USA Present address: Department of Structural Biology, Stanford University, Stanford, CA 94305, USA Present address: Whitehead Institute for Biomedical Research, Cambridge, MA 02142, USA Corresponding author e-mail:
| | - Susan L. Lindquist
- Department of Biochemistry and Molecular Biology and Department of Molecular Genetics and Cell Biology and Howard Hughes Medical Institute, the University of Chicago, Chicago, IL 60637, USA Present address: Department of Structural Biology, Stanford University, Stanford, CA 94305, USA Present address: Whitehead Institute for Biomedical Research, Cambridge, MA 02142, USA Corresponding author e-mail:
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12
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Mankouri HW, Morgan A. The DNA helicase activity of yeast Sgs1p is essential for normal lifespan but not for resistance to topoisomerase inhibitors. Mech Ageing Dev 2001; 122:1107-20. [PMID: 11389927 DOI: 10.1016/s0047-6374(01)00253-6] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
The Saccharomyces cerevisiae SGS1 gene is a member of the RecQ family of ATP-dependent DNA helicases, which includes the human WRN, BLM and RECQ4 genes. Mutations in the WRN gene cause the human premature ageing disorder, Werner's syndrome. Deletion of the SGS1 gene also causes premature ageing in yeast, suggesting that the molecular mechanisms of cellular ageing may be evolutionarily conserved. To investigate the role of the RecQ helicase domain in ageing, a point mutation (SGS1 K(706)-->A) known to eliminate the DNA helicase activity of Sgs1p was constructed. This mutant allele failed to rescue the premature ageing of the sgs1Delta strain, demonstrating that Sgs1p DNA helicase activity is required for a normal lifespan. In contrast, the SGS1 K(706)-->A allele was sufficient to rescue the hypersensitivity of the sgs1Delta strain to topoisomerase inhibitors, but not other genotoxic agents. These findings support the idea that Sgs1p fulfils multiple cellular functions, and that DNA helicase activity is dispensable for some of these (e.g. functional interaction with topoisomerases), but essential for others (e.g. longevity).
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Affiliation(s)
- H W Mankouri
- Department of Physiology, University of Liverpool, PO Box 147, Crown Street, L69 3BX, Liverpool, UK
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13
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Bryant NJ, James DE. Vps45p stabilizes the syntaxin homologue Tlg2p and positively regulates SNARE complex formation. EMBO J 2001; 20:3380-8. [PMID: 11432826 PMCID: PMC125511 DOI: 10.1093/emboj/20.13.3380] [Citation(s) in RCA: 106] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Sec1p-like/Munc-18 (SM) proteins bind to t-SNAREs and inhibit ternary complex formation. Paradoxically, the absence of SM proteins does not result in constitutive membrane fusion. Here, we show that in yeast cells lacking the SM protein Vps45p, the t-SNARE Tlg2p is down-regulated, to undetectable levels, by rapid proteasomal degradation. In the absence of Vps45p, Tlg2p can be stabilized through abolition of proteasome activity. Surprisingly, the stabilized Tlg2p was targeted to the correct intracellular location. However, the stabilized Tlg2p is non-functional and unable to bind its cognate SNARE binding partners, Tlg1p and Vti1p, in the absence of Vps45p. A truncation mutant lacking the first 230 residues of Tlg2p no longer bound Vps45p but was able to form complexes with Tlg1p and Vti1p in the absence of the SM protein. These data provide us with two valuable insights into the function of SM proteins. First, SM proteins act as chaperone-like molecules for their cognate t-SNAREs. Secondly, SM proteins play an essential role in the activation process allowing their cognate t-SNARE to participate in ternary complex formation.
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Affiliation(s)
- N J Bryant
- Institute for Molecular Biosciences, and Department of Physiology and Pharmacology, University of Queensland, St Lucia, Queensland, Australia 4072.
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14
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May AP, Whiteheart SW, Weis WI. Unraveling the mechanism of the vesicle transport ATPase NSF, the N-ethylmaleimide-sensitive factor. J Biol Chem 2001; 276:21991-4. [PMID: 11301340 DOI: 10.1074/jbc.r100013200] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Affiliation(s)
- A P May
- Department of Structural Biology and Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, California 94305, USA
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15
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Schepers A, Diffley JF. Mutational analysis of conserved sequence motifs in the budding yeast cdc6 protein 1 1Edited by M. Yaniv. J Mol Biol 2001; 308:597-608. [PMID: 11350163 DOI: 10.1006/jmbi.2001.4637] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The Cdc6 protein is required to load a complex of Mcm2-7 family members (the MCM complex) into prereplicative complexes at budding yeast origins of DNA replication. Cdc6p is a member of the AAA(+) superfamily of proteins, which includes the prokaryotic and eukaryotic clamp loading proteins. These proteins share a number of conserved regions of homology and a common three-dimensional architecture. Two of the conserved sequence motifs are the Walker A and B motifs that are involved in nucleotide metabolism and are essential for Cdc6p function in vivo. Here, we analyse mutants in the other conserved sequence motifs. Several of these mutants are temperature-sensitive for growth and are unable to recruit the MCM complex to chromatin at the restrictive temperature. In one such temperature-sensitive mutant, a highly conserved asparagine residue in the sensor I motif was changed to alanine. Overexpression of this mutant protein is lethal. This phenotype is very similar to the phenotype previously described for a mutation in the Walker B motif, suggesting a common role for sensor I and the Walker B motif in Cdc6 function.
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Affiliation(s)
- A Schepers
- Clare Hall Laboratories, Imperial Cancer Research Fund, South Mimms, EN6 3LD, UK
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16
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Karata K, Verma CS, Wilkinson AJ, Ogura T. Probing the mechanism of ATP hydrolysis and substrate translocation in the AAA protease FtsH by modelling and mutagenesis. Mol Microbiol 2001; 39:890-903. [PMID: 11251810 DOI: 10.1046/j.1365-2958.2001.02301.x] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
We have built a homology model of the AAA domain of the ATP-dependent protease FtsH of Escherichia coli based on the crystal structure of the hexamerization domain of N-ethylmaleimide-sensitive fusion protein. The resulting model of the hexameric ring of the ATP-bound form of the AAA ATPase suggests a plausible mechanism of ATP binding and hydrolysis, in which invariant residues of Walker motifs A and B and the second region of homology, characteristic of the AAA ATPases, play key roles. The importance of these invariant residues was confirmed by site-directed mutagenesis. Further modelling suggested a mechanism by which ATP hydrolysis alters the conformation of the loop forming the central hole of the hexameric ring. It is proposed that unfolded polypeptides are translocated through the central hole into the protease chamber upon cycles of ATP hydrolysis. Degradation of polypeptides by FtsH is tightly coupled to ATP hydrolysis, whereas ATP binding alone is sufficient to support the degradation of short peptides. Furthermore, comparative structural analysis of FtsH and a related ATPase, HslU, reveals interesting similarities and differences in mechanism.
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Affiliation(s)
- K Karata
- Division of Molecular Cell Biology, Institute of Molecular Embryology and Genetics, Kumamoto University, Kumamoto 862-0976, Japan
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17
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Whiteheart SW, Schraw T, Matveeva EA. N-ethylmaleimide sensitive factor (NSF) structure and function. INTERNATIONAL REVIEW OF CYTOLOGY 2001; 207:71-112. [PMID: 11352269 DOI: 10.1016/s0074-7696(01)07003-6] [Citation(s) in RCA: 96] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Our understanding of the molecular mechanisms of membrane trafficking advanced at a rapid rate during the 1990s. As one of the initial protein components of the trafficking machinery to be identified, N-ethylmaleimide sensitive factor (NSF) has served as a reference point in many of these recent studies. This hexameric ATPase is essential for most of the membrane-trafficking events in a cell. Initially, due to its ATPase activity, NSF was thought to be the motor that drove membrane fusion. Subsequent studies have shown that NSF actually plays the role of a chaperone by activating SNAP receptor proteins (SNAREs) so that they can participate in membrane fusion. In this review we will examine the initial characterization of NSF, its role in membrane fusion events, and what new structural information can tell us about NSF's mechanism of action.
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Affiliation(s)
- S W Whiteheart
- Department of Molecular and Cellular Biochemistry, University of Kentucky College of Medicine, Lexington 40536, USA
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