1
|
Mirzadeh A, Kobakhidze G, Vuillemot R, Jonic S, Rouiller I. In silico prediction, characterization, docking studies and molecular dynamics simulation of human p97 in complex with p37 cofactor. BMC Mol Cell Biol 2022; 23:39. [PMID: 36088301 PMCID: PMC9464413 DOI: 10.1186/s12860-022-00437-2] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2021] [Accepted: 07/13/2022] [Indexed: 11/10/2022] Open
Abstract
Abstract
Background
The AAA + ATPase p97 is an essential unfoldase/segragase involved in a multitude of cellular processes. It functions as a molecular machine critical for protein homeostasis, homotypic membrane fusion events and organelle biogenesis during mitosis in which it acts in concert with cofactors p47 and p37. Cofactors assist p97 in extracting and unfolding protein substrates through ATP hydrolysis. In contrast to other p97ʼs cofactors, p37 uniquely increases the ATPase activity of p97. Disease-causing mutations in p97, including mutations that cause neurodegenerative diseases, increase cofactor association with its N-domain, ATPase activity and improper substrate processing. Upregulation of p97 has also been observed in various cancers. This study aims towards the characterization of the protein–protein interaction between p97 and p37 at the atomic level. We defined the interacting residues in p97 and p37. The knowledge will facilitate the design of unique small molecules inhibiting this interaction with insights into cancer therapy and drug design.
Results
The homology model of human p37 UBX domain was built from the X-ray crystal structure of p47 C-terminus from rat (PDB code:1S3S, G) as a template and assessed by model validation analysis. According to the HDOCK, HAWKDOCK, MM-GBSA binding free energy calculations and Arpeggio, we found that there are several hydrophobic and two hydrogen-bonding interactions between p37 UBX and p97 N-D1 domain. Residues of p37 UBX predicted to be involved in the interactions with p97 N-D1 domain interface are highly conserved among UBX cofactors.
Conclusion
This study provides a reliable structural insight into the p37-p97 complex binding sites at the atomic level though molecular docking coupled with molecular dynamics simulation. This can guide the rational design of small molecule drugs for inhibiting mutant p97 activity.
Collapse
|
2
|
Choubey S, Das D, Majumdar S. Cell-to-cell variability in organelle abundance reveals mechanisms of organelle biogenesis. Phys Rev E 2020; 100:022405. [PMID: 31574672 DOI: 10.1103/physreve.100.022405] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2019] [Indexed: 12/20/2022]
Abstract
How cells regulate the number of organelles is a fundamental question in cell biology. While decades of experimental work have uncovered four fundamental processes that regulate organelle biogenesis, namely, de novo synthesis, fission, fusion, and decay, a comprehensive understanding of how these processes together control organelle abundance remains elusive. Recent fluorescence microscopy experiments allow for the counting of organelles at the single-cell level. These measurements provide information about the cell-to-cell variability in organelle abundance in addition to the mean level. Motivated by such measurements, we build upon a recent study and analyze a general stochastic model of organelle biogenesis. We compute the exact analytical expressions for the probability distribution of organelle numbers, their mean, and variance across a population of single cells. It is shown that different mechanisms of organelle biogenesis lead to distinct signatures in the distribution of organelle numbers which allow us to discriminate between these various mechanisms. By comparing our theory against published data for peroxisome abundance measurements in yeast, we show that a widely believed model of peroxisome biogenesis that involves de novo synthesis, fission, and decay is inadequate in explaining the data. Also, our theory predicts bimodality in certain limits of the model. Overall, the framework developed here can be harnessed to gain mechanistic insights into the process of organelle biogenesis.
Collapse
Affiliation(s)
- Sandeep Choubey
- Max Planck Institute for the Physics of Complex Systems, Nöthnitzerstraße 38, 01187 Dresden, Germany
| | - Dipjyoti Das
- Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, Connecticut 06511, USA
| | - Saptarshi Majumdar
- Max Planck Institute for the Physics of Complex Systems, Nöthnitzerstraße 38, 01187 Dresden, Germany
| |
Collapse
|
3
|
Schmid JA. Endoplasmosis and exoplasmosis: the evolutionary principles underlying endocytosis, exocytosis, and vesicular transport. Wien Med Wochenschr 2016; 166:236-41. [PMID: 27167530 PMCID: PMC4871923 DOI: 10.1007/s10354-016-0453-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Eukaryotic cells are characterized by a multicompartmental structure with a variety of organelles. Vesicular transport between these compartments requires membrane fusion events. Based on a membrane topology view, we conclude that there are two basic mechanisms of membrane fusion, namely where the membranes first come in contact with the cis-side (the plasmatic phase of the lipid bilayer) or with the trans-side (the extra-plasmatic face). We propose to designate trans-membrane fusion processes as “endoplasmosis” as they lead to uptake of a compartment into the plasmatic phase. Vice versa we suggest the term “exoplasmosis” (as already suggested in a 1964 publication) for cis-membrane fusion events, where the interior of a vesicle is released to an extraplasmatic environment (the extracellular space or the lumen of a compartment). This concept is supported by the fact that all cis- and all trans-membrane fusions, respectively, exhibit noticeable similarities implying that they evolved from two functionally different mechanisms.
Collapse
Affiliation(s)
- Johannes A Schmid
- Center for Physiology and Pharmacology, Department of Vascular Biology and Thrombosis Research, Medical University Vienna, Schwarzspanierstraße 17, 1090, Vienna, Austria.
| |
Collapse
|
4
|
Mukherji S, O'Shea EK. Mechanisms of organelle biogenesis govern stochastic fluctuations in organelle abundance. eLife 2014; 3:e02678. [PMID: 24916159 PMCID: PMC4046565 DOI: 10.7554/elife.02678] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2014] [Accepted: 05/05/2014] [Indexed: 11/13/2022] Open
Abstract
Fluctuations in organelle abundance can profoundly limit the precision of cell biological processes from secretion to metabolism. We modeled the dynamics of organelle biogenesis and predicted that organelle abundance fluctuations depend strongly on the specific mechanisms that increase or decrease the number of a given organelle. Our model exactly predicts the size of experimentally measured Golgi apparatus and vacuole abundance fluctuations, suggesting that cells tolerate the maximum level of variability generated by the Golgi and vacuole biogenesis pathways. We observe large increases in peroxisome abundance fluctuations when cells are transferred from glucose-rich to fatty acid-rich environments. These increased fluctuations are significantly diminished in mutants lacking peroxisome fission factors, leading us to infer that peroxisome biogenesis switches from de novo synthesis to primarily fission. Our work provides a general framework for exploring stochastic organelle biogenesis and using fluctuations to quantitatively unravel the biophysical pathways that control the abundance of subcellular structures.DOI: http://dx.doi.org/10.7554/eLife.02678.001.
Collapse
Affiliation(s)
- Shankar Mukherji
- FAS Center for Systems Biology, Harvard University, Cambridge, United States Department of Molecular and Cellular Biology, Harvard University, Cambridge, United States Howard Hughes Medical Institute, Harvard University, Cambridge, United States
| | - Erin K O'Shea
- FAS Center for Systems Biology, Harvard University, Cambridge, United States Department of Molecular and Cellular Biology, Harvard University, Cambridge, United States Howard Hughes Medical Institute, Harvard University, Cambridge, United States Department of Chemistry and Chemical Biology, Harvard University, Cambridge, United States
| |
Collapse
|
5
|
Yuan X, Shaw A, Zhang X, Kondo H, Lally J, Freemont PS, Matthews S. Solution structure and interaction surface of the C-terminal domain from p47: a major p97-cofactor involved in SNARE disassembly. J Mol Biol 2001; 311:255-63. [PMID: 11478859 DOI: 10.1006/jmbi.2001.4864] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
p47 is the major protein identified in complex with the cytosolic AAA ATPase p97. It functions as an essential cofactor of p97-regulated membrane fusion, which has been suggested to disassemble t-t-SNARE complexes and prepare them for further rounds of membrane fusion. Here, we report the high-resolution NMR structure of the C-terminal domain from p47. It comprises a UBX domain and a 13 residue long structured N-terminal extension. The UBX domain adopts a characteristic ubiquitin fold with a betabetaalphabetabetaalphabeta secondary structure arrangement. Three hydrophobic residues from the N-terminal extension pack closely against a cleft in the UBX domain. We also identify, for the first time, the p97 interaction surface using NMR chemical shift perturbation studies.
Collapse
Affiliation(s)
- X Yuan
- Department of Biological Sciences, Wolfson Laboratories, Imperial College of Science Technology and Medicine, London, South Kensington, SW7 2AY, UK
| | | | | | | | | | | | | |
Collapse
|
6
|
Roy L, Bergeron JJ, Lavoie C, Hendriks R, Gushue J, Fazel A, Pelletier A, Morré DJ, Subramaniam VN, Hong W, Paiement J. Role of p97 and syntaxin 5 in the assembly of transitional endoplasmic reticulum. Mol Biol Cell 2000; 11:2529-42. [PMID: 10930451 PMCID: PMC14937 DOI: 10.1091/mbc.11.8.2529] [Citation(s) in RCA: 85] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Transitional endoplasmic reticulum (tER) consists of confluent rough and smooth endoplasmic reticulum (ER) domains. In a cell-free incubation system, low-density microsomes (1.17 g cc(-1)) isolated from rat liver homogenates reconstitute tER by Mg(2+)GTP- and Mg(2+)ATP-hydrolysis-dependent membrane fusion. The ATPases associated with different cellular activities protein p97 has been identified as the relevant ATPase. The ATP depletion by hexokinase or treatment with either N-ethylmaleimide or anti-p97 prevented assembly of the smooth ER domain of tER. High-salt washing of low-density microsomes inhibited assembly of the smooth ER domain of tER, whereas the readdition of purified p97 with associated p47 promoted reconstitution. The t-SNARE syntaxin 5 was observed within the smooth ER domain of tER, and antisyntaxin 5 abrogated formation of this same membrane compartment. Thus, p97 and syntaxin 5 regulate assembly of the smooth ER domain of tER and hence one of the earliest membrane differentiated components of the secretory pathway.
Collapse
Affiliation(s)
- L Roy
- Département de Pathologie et Biologie Cellulaire, Faculté de Médecine, Université de Montréal, Québec, Canada
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
7
|
Sandvig K, Llorente A, Rodal SK, Eker P, Garred O, Stahlhut M, van Deurs B. Apical macropinocytosis in polarized MDCK cells: regulation by N-ethylmaleimide-sensitive proteins. Eur J Cell Biol 2000; 79:447-57. [PMID: 10961444 DOI: 10.1078/0171-9335-00071] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
In cells tested so far endocytosis seems to be dependent on N-ethylmaleimide (NEM)-sensitive proteins, and treatment with NEM results in a complete block of endocytosis. We here demonstrate that treatment of polarized MDCK I cells with NEM strongly increased endocytosis of ricin and horseradish peroxidase at the apical side, and electron microscopy revealed NEM-induced formation of large macropinosomes at the apical pole. The NEM-stimulated apical endocytosis seemed to involve phosphatidylinositol-3 kinase, protein kinase C and phospholipase D and it was dependent on ATP. Moreover, in contrast to endocytosis in nonpolarized cells ricin endocytosis at the basolateral side continued in the presence of NEM whereas endocytosis of transferrin was blocked. Furthermore, recycling of ricin endocytosed in the absence of NEM was not inhibited on either side upon addition of NEM demonstrating the existence of a NEM-resistant fusion machinery. The results suggest that the fusogenic property of both the apical and the basolateral plasma membrane of MDCK cells differs from that typically observed in cells unable to polarize.
Collapse
Affiliation(s)
- K Sandvig
- Institute for Cancer Research, The Norwegian Radium Hospital, Department of Biochemistry, Montebello, Oslo.
| | | | | | | | | | | | | |
Collapse
|
8
|
Abstract
Cell fusion is a universal process that occurs during fertilization and in the formation of organs such as muscles, placenta, and bones. Very little is known about the molecular and cellular mechanisms of cell fusion during pattern formation. Here we review the dynamic anatomy of all cell fusions during embryonic and postembryonic development in an organism. Nearly all the cell fates and cell lineages are invariant in the nematode C. elegans and one third of the cells that are born fuse to form 44 syncytia in a reproducible and stereotyped way. To explain the function of cell fusion in organ formation we propose the fusomorphogenetic model as a simple cellular mechanism to efficiently redistribute membranes using a combination of cell fusion and polarized membrane recycling during morphogenesis. Thus, regulated intercellular and intracellular membrane fusion processes may drive elongation of the embryo as well as postembryonic organ formation in C. elegans. Finally, we use the fusomorphogenetic hypothesis to explain the role of cell fusion in the formation of organs like muscles, bones, and placenta in mammals and other species and to speculate on how the intracellular machinery that drive fusomorphogenesis may have evolved.
Collapse
Affiliation(s)
- G Shemer
- Department of Biology, Technion-Israel Institute of Technology, Haifa
| | | |
Collapse
|
9
|
Dreier L, Rapoport TA. In vitro formation of the endoplasmic reticulum occurs independently of microtubules by a controlled fusion reaction. J Cell Biol 2000; 148:883-98. [PMID: 10704440 PMCID: PMC2174540 DOI: 10.1083/jcb.148.5.883] [Citation(s) in RCA: 156] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/03/2022] Open
Abstract
We have established an in vitro system for the formation of the endoplasmic reticulum (ER). Starting from small membrane vesicles prepared from Xenopus laevis eggs, an elaborate network of membrane tubules is formed in the presence of cytosol. In the absence of cytosol, the vesicles only fuse to form large spheres. Network formation requires a ubiquitous cytosolic protein and nucleoside triphosphates, is sensitive to N-ethylmaleimide and high cytosolic Ca(2+) concentrations, and proceeds via an intermediate stage in which vesicles appear to be clustered. Microtubules are not required for membrane tubule and network formation. Formation of the ER network shares significant similarities with formation of the nuclear envelope. Our results suggest that the ER network forms in a process in which cytosolic factors modify and regulate a basic reaction of membrane vesicle fusion.
Collapse
Affiliation(s)
- Lars Dreier
- Howard Hughes Medical Institute and Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115-6091
| | - Tom A. Rapoport
- Howard Hughes Medical Institute and Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115-6091
| |
Collapse
|
10
|
Bucci C, Thomsen P, Nicoziani P, McCarthy J, van Deurs B. Rab7: a key to lysosome biogenesis. Mol Biol Cell 2000; 11:467-80. [PMID: 10679007 PMCID: PMC14786 DOI: 10.1091/mbc.11.2.467] [Citation(s) in RCA: 785] [Impact Index Per Article: 32.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The molecular machinery behind lysosome biogenesis and the maintenance of the perinuclear aggregate of late endocytic structures is not well understood. A likely candidate for being part of this machinery is the small GTPase Rab7, but it is unclear whether this protein is associated with lysosomes or plays any role in the regulation of the perinuclear lysosome compartment. Previously, Rab7 has mainly been implicated in transport from early to late endosomes. We have now used a new approach to analyze the role of Rab7: transient expression of Enhanced Green Fluorescent Protein (EGFP)-tagged Rab7 wt and mutant proteins in HeLa cells. EGFP-Rab7 wt was associated with late endocytic structures, mainly lysosomes, which aggregated and fused in the perinuclear region. The size of the individual lysosomes as well as the degree of perinuclear aggregation increased with the expression levels of EGFP-Rab7 wt and, more dramatically, the active EGFP-Rab7Q67L mutant. In contrast, upon expression of the dominant-negative mutants EGFP-Rab7T22N and EGFP-Rab7N125I, which localized mainly to the cytosol, the perinuclear lysosome aggregate disappeared and lysosomes, identified by colocalization of cathepsin D and lysosome-associated membrane protein-1, became dispersed throughout the cytoplasm, they were inaccessible to endocytosed molecules such as low-density lipoprotein, and their acidity was strongly reduced, as determined by decreased accumulation of the acidotropic probe LysoTracker Red. In contrast, early endosomes associated with Rab5 and the transferrin receptor, late endosomes enriched in the cation-independent mannose 6-phosphate receptor, and the trans-Golgi network, identified by its enrichment in TGN-38, were unchanged. These data demonstrate for the first time that Rab7, controlling aggregation and fusion of late endocytic structures/lysosomes, is essential for maintenance of the perinuclear lysosome compartment.
Collapse
Affiliation(s)
- C Bucci
- Structural Cell Biology Unit, Department of Medical Anatomy, The Panum Institute, University of Copenhagen, DK-2200 Copenhagen, Denmark
| | | | | | | | | |
Collapse
|
11
|
Titorenko VI, Chan H, Rachubinski RA. Fusion of small peroxisomal vesicles in vitro reconstructs an early step in the in vivo multistep peroxisome assembly pathway of Yarrowia lipolytica. J Cell Biol 2000; 148:29-44. [PMID: 10629216 PMCID: PMC2156211 DOI: 10.1083/jcb.148.1.29] [Citation(s) in RCA: 127] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We have identified and purified six subforms of peroxisomes, designated P1 to P6, from the yeast, Yarrowia lipolytica. An analysis of trafficking of peroxisomal proteins in vivo suggests the existence of a multistep peroxisome assembly pathway in Y. lipolytica. This pathway operates by conversion of peroxisomal subforms in the direction P1, P2-->P3-->P4-->P5-->P6 and involves the import of various peroxisomal proteins into distinct vesicular intermediates. We have also reconstituted in vitro the fusion of the earliest intermediates in the pathway, small peroxisomal vesicles P1 and P2. Their fusion leads to the formation of a larger and more dense peroxisomal vesicle, P3. Fusion of P1 and P2 in vitro requires cytosol and ATP hydrolysis and is inhibited by antibodies to two membrane-associated ATPases of the AAA family, Pex1p and Pex6p. We provide evidence that the fusion in vitro of P1 and P2 peroxisomes reconstructs an actual early step in the peroxisome assembly pathway operating in vivo in Y. lipolytica.
Collapse
Affiliation(s)
- Vladimir I. Titorenko
- Department of Cell Biology, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
| | - Honey Chan
- Department of Cell Biology, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
| | | |
Collapse
|
12
|
de Figueiredo P, Polizotto RS, Drecktrah D, Brown WJ. Membrane tubule-mediated reassembly and maintenance of the Golgi complex is disrupted by phospholipase A2 antagonists. Mol Biol Cell 1999; 10:1763-82. [PMID: 10359595 PMCID: PMC25369 DOI: 10.1091/mbc.10.6.1763] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Although membrane tubules can be found extending from, and associated with, the Golgi complex of eukaryotic cells, their physiological function has remained unclear. To gain insight into the biological significance of membrane tubules, we have developed methods for selectively preventing their formation. We show here that a broad range of phospholipase A2 (PLA2) antagonists not only arrest membrane tubule-mediated events that occur late in the assembly of the Golgi complex but also perturb its normal steady-state tubulovesicular architecture by inducing a reversible fragmentation into separate "mini-stacks." In addition, we show that these same compounds prevent the formation of membrane tubules from Golgi stacks in an in vitro reconstitution system. This in vitro assay was further used to demonstrate that the relevant PLA2 activity originates from the cytoplasm. Taken together, these results demonstrate that Golgi membrane tubules, sensitive to potent and selective PLA2 antagonists, mediate both late events in the reassembly of the Golgi complex and the dynamic maintenance of its steady-state architecture. In addition, they implicate a role for cytoplasmic PLA2 enzymes in mediating these membrane trafficking events.
Collapse
Affiliation(s)
- P de Figueiredo
- Section of Biochemistry, Molecular, and Cell Biology, Cornell University, Ithaca, New York 14853, USA
| | | | | | | |
Collapse
|
13
|
Hermann GJ, Thatcher JW, Mills JP, Hales KG, Fuller MT, Nunnari J, Shaw JM. Mitochondrial fusion in yeast requires the transmembrane GTPase Fzo1p. J Cell Biol 1998; 143:359-73. [PMID: 9786948 PMCID: PMC2132826 DOI: 10.1083/jcb.143.2.359] [Citation(s) in RCA: 425] [Impact Index Per Article: 16.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/1998] [Revised: 08/25/1998] [Indexed: 01/09/2023] Open
Abstract
Membrane fusion is required to establish the morphology and cellular distribution of the mitochondrial compartment. In Drosophila, mutations in the fuzzy onions (fzo) GTPase block a developmentally regulated mitochondrial fusion event during spermatogenesis. Here we report that the yeast orthologue of fuzzy onions, Fzo1p, plays a direct and conserved role in mitochondrial fusion. A conditional fzo1 mutation causes the mitochondrial reticulum to fragment and blocks mitochondrial fusion during yeast mating. Fzo1p is a mitochondrial integral membrane protein with its GTPase domain exposed to the cytoplasm. Point mutations that alter conserved residues in the GTPase domain do not affect Fzo1p localization but disrupt mitochondrial fusion. Suborganellar fractionation suggests that Fzo1p spans the outer and is tightly associated with the inner mitochondrial membrane. This topology may be required to coordinate the behavior of the two mitochondrial membranes during the fusion reaction. We propose that the fuzzy onions family of transmembrane GTPases act as molecular switches to regulate a key step in mitochondrial membrane docking and/or fusion.
Collapse
Affiliation(s)
- G J Hermann
- Department of Biology, University of Utah, Salt Lake City, Utah 84112, USA
| | | | | | | | | | | | | |
Collapse
|
14
|
|
15
|
Hernandez LD, Peters RJ, Delos SE, Young JA, Agard DA, White JM. Activation of a retroviral membrane fusion protein: soluble receptor-induced liposome binding of the ALSV envelope glycoprotein. J Biophys Biochem Cytol 1997; 139:1455-64. [PMID: 9396751 PMCID: PMC2132611 DOI: 10.1083/jcb.139.6.1455] [Citation(s) in RCA: 104] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
It is not known how membrane fusion proteins that function at neutral pH, for example the human immunodeficiency virus envelope (Env) glycoprotein and intracellular fusion machines, are activated for target bilayer binding. We have addressed this question using a soluble oligomeric form of an avian retroviral Env glycoprotein (API) and soluble forms of its receptor. Binding of soluble receptor to API induces API to bind to liposomes composed of phosphatidylcholine and cholesterol at neutral pH. Liposome binding only occurs at fusion permissive temperatures (T > 20 degrees C), is complete between 2 to 5 min at 37 degrees C, and is stable to high salt, carbonate, and urea. Liposome binding is mediated by the ectodomain of the transmembrane subunit of API, and a mutant with a Val to Glu substitution in the Env fusion peptide (located in the ectodomain of the transmembrane subunit) shows significantly reduced liposome binding. Moreover, under conditions of equivalent binding to API, a mutant receptor that does not support infection (Zingler, K., and J.A.T. Young. 1996. J. Virol. 70:7510-7516) does not induce significant liposome binding. Our results indicate that a highly specific interaction between an avian retroviral Env and its receptor activates the retroviral glycoprotein for target bilayer binding at neutral pH in much the same way as low pH activates the influenza hemagglutinin. Our findings are discussed in terms of the mechanisms of viral and cellular fusion proteins that function at neutral pH.
Collapse
Affiliation(s)
- L D Hernandez
- Department of Cell Biology, University of Virginia Health Sciences Center, Charlottesville, Virginia 22908, USA
| | | | | | | | | | | |
Collapse
|
16
|
Abstract
Small GTPases of the Rab subfamily have been known to be key regulators of intracellular membrane traffic since the late 1980s. Today this protein group amounts to more than 40 members in mammalian cells which localize to distinct membrane compartments and exert functions in different trafficking steps on the biosynthetic and endocytic pathways. Recent studies indicate that cycles of GTP binding and hydrolysis by the Rab proteins are linked to the recruitment of specific effector molecules on cellular membranes, which in turn impact on membrane docking/fusion processes. Different Rabs may, nevertheless, have slightly different principles of action. Studies performed in yeast suggest that connections between the Rabs and the SNARE machinery play a central role in membrane docking/fusion. Further elucidation of this linkage is required in order to fully understand the functional mechanisms of Rab GTPases in membrane traffic.
Collapse
Affiliation(s)
- V M Olkkonen
- National Public Health Institute, Helsinki, Finland
| | | |
Collapse
|
17
|
Abstract
The Drosophila Fzo protein is required for mitochondrial fusion during a key step in sperm formation. This novel, membrane-bound GTPase defines a family of proteins that may mediate mitochondrial fusion in a variety of eukaryotic cells.
Collapse
Affiliation(s)
- M P Yaffe
- Department of Biology, University of California, San Diego, La Jolla, California 92093-0347, USA.
| |
Collapse
|
18
|
Titorenko VI, Ogrydziak DM, Rachubinski RA. Four distinct secretory pathways serve protein secretion, cell surface growth, and peroxisome biogenesis in the yeast Yarrowia lipolytica. Mol Cell Biol 1997; 17:5210-26. [PMID: 9271399 PMCID: PMC232372 DOI: 10.1128/mcb.17.9.5210] [Citation(s) in RCA: 106] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
We have identified and characterized mutants of the yeast Yarrowia lipolytica that are deficient in protein secretion, in the ability to undergo dimorphic transition from the yeast to the mycelial form, and in peroxisome biogenesis. Mutations in the SEC238, SRP54, PEX1, PEX2, PEX6, and PEX9 genes affect protein secretion, prevent the exit of the precursor form of alkaline extracellular protease from the endoplasmic reticulum, and compromise peroxisome biogenesis. The mutants sec238A, srp54KO, pex2KO, pex6KO, and pex9KO are also deficient in the dimorphic transition from the yeast to the mycelial form and are affected in the export of only plasma membrane and cell wall-associated proteins specific for the mycelial form. Mutations in the SEC238, SRP54, PEX1, and PEX6 genes prevent or significantly delay the exit of two peroxisomal membrane proteins, Pex2p and Pex16p, from the endoplasmic reticulum en route to the peroxisomal membrane. Mutations in the PEX5, PEX16, and PEX17 genes, which have previously been shown to be essential for peroxisome biogenesis, affect the export of plasma membrane and cell wall-associated proteins specific for the mycelial form but do not impair exit from the endoplasmic reticulum of either Pex2p and Pex16p or of proteins destined for secretion. Biochemical analyses of these mutants provide evidence for the existence of four distinct secretory pathways that serve to deliver proteins for secretion, plasma membrane and cell wall synthesis during yeast and mycelial modes of growth, and peroxisome biogenesis. At least two of these secretory pathways, which are involved in the export of proteins to the external medium and in the delivery of proteins for assembly of the peroxisomal membrane, diverge at the level of the endoplasmic reticulum.
Collapse
Affiliation(s)
- V I Titorenko
- Department of Cell Biology and Anatomy, University of Alberta, Edmonton, Canada
| | | | | |
Collapse
|
19
|
Storrie B, Desjardins M. The biogenesis of lysosomes: is it a kiss and run, continuous fusion and fission process? Bioessays 1996; 18:895-903. [PMID: 8939067 DOI: 10.1002/bies.950181108] [Citation(s) in RCA: 101] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/02/1996] [Indexed: 02/03/2023]
Abstract
Molecules are transferred to lysosomes, the major, acid pH, digestive compartment in eukaryotic cells, by a complex series of pathways that converge at a late endosome/prelysosomal compartment. Here, we discuss the relationship between this compartment and the lysosome. We propose that lysosomes are maintained within cells by a repeated series of kiss and run, transient fusion and fission processes with the late endosome/prelysosome compartment. Directionality to these processes may be conferred by pH gradients and retrieval mechanisms. The future challenge in testing this and any other proposed hypothesis for lysosomal biogenesis will be the establishment of molecular mechanisms.
Collapse
Affiliation(s)
- B Storrie
- Department of Biochemistry, Virginia Polytechnic Institute and State University, Blacksburg 24061-0308, USA.
| | | |
Collapse
|