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de Sautu M, Herrmann T, Scanavachi G, Jenni S, Harrison SC. The rotavirus VP5*/VP8* conformational transition permeabilizes membranes to Ca2. PLoS Pathog 2024; 20:e1011750. [PMID: 38574119 PMCID: PMC11020617 DOI: 10.1371/journal.ppat.1011750] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2023] [Revised: 04/16/2024] [Accepted: 03/04/2024] [Indexed: 04/06/2024] Open
Abstract
Rotaviruses infect cells by delivering into the cytosol a transcriptionally active inner capsid particle (a "double-layer particle": DLP). Delivery is the function of a third, outer layer, which drives uptake from the cell surface into small vesicles from which the DLPs escape. In published work, we followed stages of rhesus rotavirus (RRV) entry by live-cell imaging and correlated them with structures from cryogenic electron microscopy and tomography (cryo-EM and cryo-ET). The virus appears to wrap itself in membrane, leading to complete engulfment and loss of Ca2+ from the vesicle produced by the wrapping. One of the outer-layer proteins, VP7, is a Ca2+-stabilized trimer; loss of Ca2+ releases both VP7 and the other outer-layer protein, VP4, from the particle. VP4, activated by cleavage into VP8* and VP5*, is a trimer that undergoes a large-scale conformational rearrangement, reminiscent of the transition that viral fusion proteins undergo to penetrate a membrane. The rearrangement of VP5* thrusts a 250-residue, C-terminal segment of each of the three subunits outward, while allowing the protein to remain attached to the virus particle and to the cell being infected. We proposed that this segment inserts into the membrane of the target cell, enabling Ca2+ to cross. In the work reported here, we show the validity of key aspects of this proposed sequence. By cryo-EM studies of liposome-attached virions ("triple-layer particles": TLPs) and single-particle fluorescence imaging of liposome-attached TLPs, we confirm insertion of the VP4 C-terminal segment into the membrane and ensuing generation of a Ca2+ "leak". The results allow us to formulate a molecular description of early events in entry. We also discuss our observations in the context of other work on double-strand RNA virus entry.
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Affiliation(s)
- Marilina de Sautu
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts, United States of America
- Laboratory of Molecular Medicine, Boston Children’s Hospital, Boston, Massachusetts, United States of America
| | - Tobias Herrmann
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Gustavo Scanavachi
- Department of Cell Biology, Harvard Medical School, Boston, Massachusetts, United States of America
- Program in Cellular and Molecular Medicine, Boston Children’s Hospital, Boston, Massachusetts, United States of America
| | - Simon Jenni
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Stephen C. Harrison
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts, United States of America
- Laboratory of Molecular Medicine, Boston Children’s Hospital, Boston, Massachusetts, United States of America
- Howard Hughes Medical Institute, Harvard Medical School, Boston, Massachusetts, United States of America
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De Sautu M, Herrmann T, Jenni S, Harrison SC. The rotavirus VP5*/VP8* conformational transition permeabilizes membranes to Ca 2. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.10.15.562449. [PMID: 37905109 PMCID: PMC10614792 DOI: 10.1101/2023.10.15.562449] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/02/2023]
Abstract
Rotaviruses infect cells by delivering into the cytosol a transcriptionally active inner capsid particle (a "double-layer particle": DLP). Delivery is the function of a third, outer layer, which drives uptake from the cell surface into small vesicles from which the DLPs escape. In published work, we followed stages of rhesus rotavirus (RRV) entry by live-cell imaging and correlated them with structures from cryogenic electron microscopy and tomography (cryo-EM and cryo-ET). The virus appears to wrap itself in membrane, leading to complete engulfment and loss of Ca2+ from the vesicle produced by the wrapping. One of the outer-layer proteins, VP7, is a Ca2+-stabilized trimer; loss of Ca2+ releases both outer-layer proteins from the particle. The other outer-layer protein, VP4, activated by cleavage into VP8* and VP5*, is a trimer that undergoes a large-scale conformational rearrangement, reminiscent of the transition that viral fusion proteins undergo to penetrate a membrane. The rearrangement of VP5* thrusts a 250-residue, C-terminal segment of each of the three subunits outward, while allowing the protein to remain attached to the virus particle and to the cell being infected. We proposed that this segment inserts into the membrane of the target cell, enabling Ca2+ to cross. In the work reported here, we show the validity of key aspects of this proposed sequence. By cryo-EM studies of liposome-attached virions ("triple-layer particles": TLPs) and single-particle fluorescence imaging of liposome-attached TLPs, we confirm insertion of the VP4 C-terminal segment into the membrane and ensuing generation of a Ca2+ "leak". The results allow us to formulate a molecular description of early events in entry. We also discuss our observations in the context of other work on double-strand RNA virus entry.
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Affiliation(s)
- Marilina De Sautu
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 250 Longwood Avenue, Boston, MA 02115, USA
- Laboratory of Molecular Medicine, Boston Children’s Hospital, Boston, MA 02115, USA
| | - Tobias Herrmann
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 250 Longwood Avenue, Boston, MA 02115, USA
| | - Simon Jenni
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 250 Longwood Avenue, Boston, MA 02115, USA
| | - Stephen C. Harrison
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 250 Longwood Avenue, Boston, MA 02115, USA
- Laboratory of Molecular Medicine, Boston Children’s Hospital, Boston, MA 02115, USA
- Howard Hughes Medical Institute, Harvard Medical School, Boston, MA 02115, USA
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Abstract
Rotavirus (RV), the most common cause of gastroenteritis in children, carries a high economic and health burden worldwide. RV encodes six structural proteins and six nonstructural proteins (NSPs) that play different roles in viral replication. NSP4, a multifunctional protein involved in various viral replication processes, has two conserved N-glycosylation sites; however, the role of glycans remains elusive. Here, we used recombinant viruses generated by a reverse genetics system to determine the role of NSP4 N-glycosylation during viral replication and pathogenesis. The growth rate of recombinant viruses that lost one glycosylation site was as high as that of the wild-type virus. However, a recombinant virus that lost both glycosylation sites (glycosylation-defective virus) showed attenuated replication in cultured cell lines. Specifically, replications of glycosylation-defective virus in MA104 and HT29 cells were 10- and 100,000-fold lower, respectively, than that of the wild-type, suggesting that N-glycosylation of NSP4 plays a critical role in RV replication. The glycosylation-defective virus showed NSP4 mislocalization, delay of cytosolic Ca2+ elevation, and less viroplasm formation in MA104 cells; however, these impairments were not observed in HT29 cells. Further analysis revealed that assembly of glycosylation-defective virus was severely impaired in HT29 cells but not in MA104 cells, suggesting that RV replication mechanism is highly cell type dependent. In vivo mouse experiments also showed that the glycosylation-defective virus was less pathogenic than the wild-type virus. Taken together, the data suggest that N-glycosylation of NSP4 plays a vital role in viral replication and pathogenicity. IMPORTANCE Rotavirus is the main cause of gastroenteritis in young children and infants worldwide, contributing to 128,500 deaths each year. Here, we used a reverse genetics approach to examine the role of NSP4 N-glycosylation. An N-glycosylation-defective virus showed attenuated and cell-type-dependent replication in vitro. In addition, mice infected with the N-glycosylation-defective virus had less severe diarrhea than mice infected with the wild type. These results suggest that N-glycosylation affects viral replication and pathogenesis. Considering the reduced pathogenicity in vivo and the high propagation rate in MA104 cells, this glycosylation-defective virus could be an ideal live attenuated vaccine candidate.
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Motayo BO, Faneye AO, Adeniji JA. VP7, VP4, and NSP4 genes of species a rotaviruses isolated from sewage in Nigeria, 2014/2015: partial sequence characterization and biophysical analysis of NSP4 (enterotoxin). Virus Genes 2022; 58:180-187. [PMID: 35303217 DOI: 10.1007/s11262-022-01895-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2021] [Accepted: 03/08/2022] [Indexed: 10/18/2022]
Abstract
Species A rotavirus are an important cause of childhood gastroenteritis, and the main contributor to its pathogenicity is the enterotoxin (NSP4) protein. Some biophysical properties of partial NSP4 genes of RVAs isolated from sewage in Nigeria during 2014/2015 were investigated. Samples were typed by RT-PCR and Sanger sequencing of partial VP4, VP7 and NSP4 genes. Phylogeny identified lineages within genotypes, predicted glycosylation sites; hydrophobicity profiles and amino acid alignments were employed to determine some biophysical properties of the NSP4 protein. The VP7 sequences of our isolates were the most diversified, the majority of the isolates carried NSP4 genes of the E1 genotype. Genotype specific variations both in hydrophobicity and potential glycosylation were identified, mutations were highest within the H3 hydrophobic domain and VP4 binding domain. The study of RVA NSP4 genes from non-clinical samples revealed that there were structural consistencies with those of reference genes.
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Affiliation(s)
- Babatunde O Motayo
- Department of Medical Microbiology, Federal Medical Center, Abeokuta, Nigeria.
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Hoxie I, Dennehy JJ. Rotavirus A Genome Segments Show Distinct Segregation and Codon Usage Patterns. Viruses 2021; 13:v13081460. [PMID: 34452326 PMCID: PMC8402926 DOI: 10.3390/v13081460] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2021] [Revised: 07/05/2021] [Accepted: 07/07/2021] [Indexed: 12/29/2022] Open
Abstract
Reassortment of the Rotavirus A (RVA) 11-segment dsRNA genome may generate new genome constellations that allow RVA to expand its host range or evade immune responses. Reassortment may also produce phylogenetic incongruities and weakly linked evolutionary histories across the 11 segments, obscuring reassortment-specific epistasis and changes in substitution rates. To determine the co-segregation patterns of RVA segments, we generated time-scaled phylogenetic trees for each of the 11 segments of 789 complete RVA genomes isolated from mammalian hosts and compared the segments’ geodesic distances. We found that segments 4 (VP4) and 9 (VP7) occupied significantly different tree spaces from each other and from the rest of the genome. By contrast, segments 10 and 11 (NSP4 and NSP5/6) occupied nearly indistinguishable tree spaces, suggesting strong co-segregation. Host-species barriers appeared to vary by segment, with segment 9 (VP7) presenting the weakest association with host species. Bayesian Skyride plots were generated for each segment to compare relative genetic diversity among segments over time. All segments showed a dramatic decrease in diversity around 2007 coinciding with the introduction of RVA vaccines. To assess selection pressures, codon adaptation indices and relative codon deoptimization indices were calculated with respect to different host genomes. Codon usage varied by segment with segment 11 (NSP5) exhibiting significantly higher adaptation to host genomes. Furthermore, RVA codon usage patterns appeared optimized for expression in humans and birds relative to the other hosts examined, suggesting that translational efficiency is not a barrier in RVA zoonosis.
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Affiliation(s)
- Irene Hoxie
- Biology Department, The Graduate Center, The City University of New York, New York, NY 10016, USA;
- Biology Department, Queens College, The City University of New York, Flushing, New York, NY 11367, USA
- Correspondence:
| | - John J. Dennehy
- Biology Department, The Graduate Center, The City University of New York, New York, NY 10016, USA;
- Biology Department, Queens College, The City University of New York, Flushing, New York, NY 11367, USA
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The Guanine Nucleotide Exchange Factor GBF1 Participates in Rotavirus Replication. J Virol 2019; 93:JVI.01062-19. [PMID: 31270230 DOI: 10.1128/jvi.01062-19] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2019] [Accepted: 07/01/2019] [Indexed: 01/06/2023] Open
Abstract
Cellular and viral factors participate in the replication cycle of rotavirus. We report that the guanine nucleotide exchange factor GBF1, which activates the small GTPase Arf1 to induce COPI transport processes, is required for rotavirus replication since knocking down GBF1 expression by RNA interference or inhibiting its activity by treatment with brefeldin A (BFA) or Golgicide A (GCA) significantly reduces the yield of infectious viral progeny. This reduction in virus yield was related to a block in virus assembly, since in the presence of either BFA or GCA, the assembly of infectious mature triple-layered virions was significantly prevented and only double-layered particles were detected. We report that the catalytic activity of GBF1, but not the activation of Arf1, is essential for the assembly of the outer capsid of rotavirus. We show that both BFA and GCA, as well as interfering with the synthesis of GBF1, alter the electrophoretic mobility of glycoproteins VP7 and NSP4 and block the trimerization of the virus surface protein VP7, a step required for its incorporation into virus particles. Although a posttranslational modification of VP7 (other than glycosylation) could be related to the lack of trimerization, we found that NSP4 might also be involved in this process, since knocking down its expression reduces VP7 trimerization. In support, recombinant VP7 protein overexpressed in transfected cells formed trimers only when cotransfected with NSP4.IMPORTANCE Rotavirus, a member of the family Reoviridae, is the major cause of severe diarrhea in children and young animals worldwide. Despite significant advances in the characterization of the biology of this virus, the mechanisms involved in morphogenesis of the virus particle are still poorly understood. In this work, we show that the guanine nucleotide exchange factor GBF1, relevant for COPI/Arf1-mediated cellular vesicular transport, participates in the replication cycle of the virus, influencing the correct processing of viral glycoproteins VP7 and NSP4 and the assembly of the virus surface proteins VP7 and VP4.
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7
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Kumar S, Ramappa R, Pamidimukkala K, Rao CD, Suguna K. New tetrameric forms of the rotavirus NSP4 with antiparallel helices. Arch Virol 2018; 163:1531-1547. [DOI: 10.1007/s00705-018-3753-6] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2017] [Accepted: 01/13/2018] [Indexed: 01/05/2023]
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Ben Hadj Fredj M, Ben Hamida-Rebaï M, Zeller M, Heylen E, Van Ranst M, Matthijnssens J, Trabelsi A. Sequence and structural analyses of NSP4 proteins from human group A rotavirus strains detected in Tunisia. ACTA ACUST UNITED AC 2014; 62:146-51. [PMID: 24679587 DOI: 10.1016/j.patbio.2013.10.006] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2013] [Accepted: 10/08/2013] [Indexed: 12/15/2022]
Abstract
BACKGROUND The NSP4 protein of group A rotavirus (RVA) has been recognized as a viral enterotoxin and plays important roles in viral pathogenesis and morphogenesis. Domains involved in structural and functional interactions have been proposed mainly based on the simian SA11 strain. METHODS NSP4 has been classified into 15 different genotypes (E1-E15), and the aim of this study was to analyze the sequences of 46 RVA strains in order to determine the aminoacid (aa) differences between E1 and E2 genotypes. Another aspect was to characterize the structural and physicochemical properties of these strains. RESULTS Comparison of deduced aa sequences of the NSP4 protein showed that divergences between NSP4 genotypes E1 and E2 were mostly observed in the VP4-binding, the interspecies variable domain (ISVD) and the double-layered particle (DLP) binding domains. Interestingly, uncommon variations in residues 131 and 138, which are known to be important aa in pathogenesis, were found in one unusual animal derived strain belonging to the E2 genotype. Concerning the structural aspect, no significant differences were noted. CONCLUSION The presence of punctual aa variations in the NSP4 genotypes may indicate that NSP4 mutates mainly via accumulation of point mutations.
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Affiliation(s)
- M Ben Hadj Fredj
- UR06SP20, Laboratory of Microbiology, Sahloul University Hospital, 4054 Sousse, Tunisia; Faculty of Pharmacy, University of Monastir, avenue Avicenne, 5019 Monastir, Tunisia
| | - M Ben Hamida-Rebaï
- UR06SP20, Laboratory of Microbiology, Sahloul University Hospital, 4054 Sousse, Tunisia; Faculty of Pharmacy, University of Monastir, avenue Avicenne, 5019 Monastir, Tunisia
| | - M Zeller
- Laboratory of Clinical and Epidemiological Virology, Department of Microbiology and Immunology, Rega Institute for Medical Research, University of Leuven, 1, place de l'Université, 1348 Louvain-La-Neuve, Belgium
| | - E Heylen
- Laboratory of Clinical and Epidemiological Virology, Department of Microbiology and Immunology, Rega Institute for Medical Research, University of Leuven, 1, place de l'Université, 1348 Louvain-La-Neuve, Belgium
| | - M Van Ranst
- Laboratory of Clinical and Epidemiological Virology, Department of Microbiology and Immunology, Rega Institute for Medical Research, University of Leuven, 1, place de l'Université, 1348 Louvain-La-Neuve, Belgium
| | - J Matthijnssens
- Laboratory of Clinical and Epidemiological Virology, Department of Microbiology and Immunology, Rega Institute for Medical Research, University of Leuven, 1, place de l'Université, 1348 Louvain-La-Neuve, Belgium
| | - A Trabelsi
- UR06SP20, Laboratory of Microbiology, Sahloul University Hospital, 4054 Sousse, Tunisia; Faculty of Pharmacy, University of Monastir, avenue Avicenne, 5019 Monastir, Tunisia.
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9
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González-Ochoa G, Menchaca GE, Hernández CE, Rodríguez C, Tamez RS, Contreras JF. Mutation distribution in the NSP4 protein in rotaviruses isolated from Mexican children with moderate to severe gastroenteritis. Viruses 2013; 5:792-805. [PMID: 23478638 PMCID: PMC3705296 DOI: 10.3390/v5030792] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2013] [Revised: 03/04/2013] [Accepted: 03/05/2013] [Indexed: 01/08/2023] Open
Abstract
The NSP4 protein is a multifunctional protein that plays a role in the morphogenesis and pathogenesis of the rotavirus. Although NSP4 is considered an enterotoxin, the relationship between gastroenteritis severity and amino acid variations in NSP4 of the human rotavirus remains unclear. In this study, we analyzed the sequence diversity of NSP4 and the severity of gastroenteritis of children with moderate to severe gastroenteritis. The rotavirus-infected children were hospitalized before the rotavirus vaccine program in Mexico. All children had diarrhea within 1-4 days, 44 (88%) were vomiting and 35 (70%) had fevers. The severity analysis showed that 13 (26%) cases had mild gastroenteritis, 23 (46%) moderate gastroenteritis and 14 (28%) severe. NSP4 phylogenetic analysis showed three clusters within the genotype E1. Sequence analysis revealed similar mutations inside each cluster, and an uncommon variation in residue 144 was found in five of the Mexican NSP4 sequences. Most of the amino acid variations were located in the VP4 and VP6 binding site domains, with no relationship to different grades of gastroenteritis. This finding indicates that severe gastroenteritis caused by the rotavirus appears to be related to diverse viral or cellular factors instead of NSP4 activity as a unique pathogenic factor.
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Affiliation(s)
- Guadalupe González-Ochoa
- Facultad de Ciencias Biológicas, Universidad Autónoma de Nuevo León, Av. Universidad S/N Ciudad Universitaria, San Nicolás de los Garza, Nuevo León, CP. 66451, Mexico.
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Bhowmick R, Halder UC, Chattopadhyay S, Chanda S, Nandi S, Bagchi P, Nayak MK, Chakrabarti O, Kobayashi N, Chawla-Sarkar M. Rotaviral enterotoxin nonstructural protein 4 targets mitochondria for activation of apoptosis during infection. J Biol Chem 2012; 287:35004-35020. [PMID: 22888003 DOI: 10.1074/jbc.m112.369595] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Viruses have evolved to encode multifunctional proteins to control the intricate cellular signaling pathways by using very few viral proteins. Rotavirus is known to express six nonstructural and six structural proteins. Among them, NSP4 is the enterotoxin, known to disrupt cellular Ca(2+) homeostasis by translocating to endoplasmic reticulum. In this study, we have observed translocation of NSP4 to mitochondria resulting in dissipation of mitochondrial membrane potential during virus infection and NSP4 overexpression. Furthermore, transfection of the N- and C-terminal truncated NSP4 mutants followed by analyzing NSP4 localization by immunofluorescence microscopy identified the 61-83-amino acid region as the shortest mitochondrial targeting signal. NSP4 exerts its proapoptotic effect by interacting with mitochondrial proteins adenine nucleotide translocator and voltage-dependent anion channel, resulting in dissipation of mitochondrial potential, release of cytochrome c from mitochondria, and caspase activation. During early infection, apoptosis activation by NSP4 was inhibited by the activation of cellular survival pathways (PI3K/AKT), because PI3K inhibitor results in early induction of apoptosis. However, in the presence of both PI3K inhibitor and NSP4 siRNA, apoptosis was delayed suggesting that the early apoptotic signal is initiated by NSP4 expression. This proapoptotic function of NSP4 is balanced by another virus-encoded protein, NSP1, which is implicated in PI3K/AKT activation because overexpression of both NSP4 and NSP1 in cells resulted in reduced apoptosis compared with only NSP4-expressing cells. Overall, this study reports on the mechanism by which enterotoxin NSP4 exerts cytotoxicity and the mechanism by which virus counteracts it at the early stage for efficient infection.
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Affiliation(s)
- Rahul Bhowmick
- Division of Virology, National Institute of Cholera and Enteric Diseases, P-33, C.I.T. Road Scheme-XM, Beliaghata, Kolkata 700010, India
| | - Umesh Chandra Halder
- Division of Virology, National Institute of Cholera and Enteric Diseases, P-33, C.I.T. Road Scheme-XM, Beliaghata, Kolkata 700010, India
| | - Shiladitya Chattopadhyay
- Division of Virology, National Institute of Cholera and Enteric Diseases, P-33, C.I.T. Road Scheme-XM, Beliaghata, Kolkata 700010, India
| | - Shampa Chanda
- Division of Virology, National Institute of Cholera and Enteric Diseases, P-33, C.I.T. Road Scheme-XM, Beliaghata, Kolkata 700010, India
| | - Satabdi Nandi
- Division of Virology, National Institute of Cholera and Enteric Diseases, P-33, C.I.T. Road Scheme-XM, Beliaghata, Kolkata 700010, India
| | - Parikshit Bagchi
- Division of Virology, National Institute of Cholera and Enteric Diseases, P-33, C.I.T. Road Scheme-XM, Beliaghata, Kolkata 700010, India
| | - Mukti Kant Nayak
- Department of Zoology, University of Calcutta, Ballygunge, Kolkata 700019, India
| | - Oishee Chakrabarti
- Structural Genomics Section, Saha Institute of Nuclear Physics, Kolkata 700064, India
| | | | - Mamta Chawla-Sarkar
- Division of Virology, National Institute of Cholera and Enteric Diseases, P-33, C.I.T. Road Scheme-XM, Beliaghata, Kolkata 700010, India.
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Hu L, Crawford SE, Hyser JM, Estes MK, Prasad BVV. Rotavirus non-structural proteins: structure and function. Curr Opin Virol 2012; 2:380-8. [PMID: 22789743 DOI: 10.1016/j.coviro.2012.06.003] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2012] [Revised: 06/13/2012] [Accepted: 06/13/2012] [Indexed: 10/28/2022]
Abstract
The replication of rotavirus is a complex process that is orchestrated by an exquisite interplay between the rotavirus non-structural and structural proteins. Subsequent to particle entry and genome transcription, the non-structural proteins coordinate and regulate viral mRNA translation and the formation of electron-dense viroplasms that serve as exclusive compartments for genome replication, genome encapsidation and capsid assembly. In addition, non-structural proteins are involved in antagonizing the antiviral host response and in subverting important cellular processes to enable successful virus replication. Although far from complete, new structural studies, together with functional studies, provide substantial insight into how the non-structural proteins coordinate rotavirus replication. This brief review highlights our current knowledge of the structure-function relationships of the rotavirus non-structural proteins, as well as fascinating questions that remain to be understood.
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Affiliation(s)
- Liya Hu
- Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX 77030, United States
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12
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Elucidation of the Rotavirus NSP4-Caveolin-1 and -Cholesterol Interactions Using Synthetic Peptides. JOURNAL OF AMINO ACIDS 2012; 2012:575180. [PMID: 22500212 PMCID: PMC3303745 DOI: 10.1155/2012/575180] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/08/2011] [Accepted: 11/16/2011] [Indexed: 01/19/2023]
Abstract
Rotavirus (RV) NSP4, the first described viral enterotoxin, is a multifunctional glycoprotein that contributes to viral pathogenesis, morphogenesis, and replication. NSP4 binds both termini of caveolin-1 and is isolated from caveolae fractions that are rich in anionic phospholipids and cholesterol. These interactions indicate that cholesterol/caveolin-1 plays a role in NSP4 transport to the cell surface, which is essential to its enterotoxic activity. Synthetic peptides were utilized to identify target(s) of intervention by exploring the NSP4-caveolin-1 and -cholesterol interactions. NSP4112–140 that overlaps the caveolin-1 binding domain and a cholesterol recognition amino acid consensus (CRAC) motif and both termini of caveolin-1 (N-caveolin-12–20, 19–40 and C-caveolin-1161–180) were synthesized. Direct fluorescence-binding assays were employed to determine binding affinities of the NSP4-caveolin-1 peptides and cholesterol. Intracellular cholesterol alteration revealed a redistribution of NSP4 and disintegration of viroplasms. These data further imply interruption of NSP4112–140-N-caveolin-119–40 and cholesterol interactions may block NSP4 intracellular transport, hence enterotoxicity.
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13
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Structural insights into the coupling of virion assembly and rotavirus replication. Nat Rev Microbiol 2012; 10:165-77. [PMID: 22266782 DOI: 10.1038/nrmicro2673] [Citation(s) in RCA: 148] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Viral replication is rapid and robust, but it is far from a chaotic process. Instead, successful production of infectious progeny requires that events occur in the correct place and at the correct time. Rotaviruses (segmented double-stranded RNA viruses of the Reoviridae family) seem to govern their replication through ordered disassembly and assembly of a triple-layered icosahedral capsid. In recent years, high-resolution structural data have provided unprecedented insight into these events. In this Review, we explore the current understanding of rotavirus replication and how it compares to replication of other Reoviridae family members.
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Didsbury A, Wang C, Verdon D, Sewell MA, McIntosh JD, Taylor JA. Rotavirus NSP4 is secreted from infected cells as an oligomeric lipoprotein and binds to glycosaminoglycans on the surface of non-infected cells. Virol J 2011; 8:551. [PMID: 22185400 PMCID: PMC3305486 DOI: 10.1186/1743-422x-8-551] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2011] [Accepted: 12/20/2011] [Indexed: 12/22/2022] Open
Abstract
Background Nonstructural glycoprotein 4 (NSP4) encoded by rotavirus is the only viral protein currently believed to function as an enterotoxin. NSP4 is synthesized as an intracellular transmembrane glycoprotein and as such is essential for virus assembly. Infection of polarized Caco-2 cells with rotavirus also results in the secretion of glycosylated NSP4 apparently in a soluble form despite retention of its transmembrane domain. We have examined the structure, solubility and cell-binding properties of this secreted form of NSP4 to further understand the biochemical basis for its enterotoxic function. We show here that NSP4 is secreted as discrete detergent-sensitive oligomers in a complex with phospholipids and demonstrate that this secreted form of NSP4 can bind to glycosaminoglycans present on the surface of a range of different cell types. Methods NSP4 was purified from the medium of infected cells after ultracentrifugation and ultrafiltration by successive lectin-affinity and ion exchange chromatography. Oligomerisation of NSP4 was examined by density gradient centrifugation and chemical crosslinking and the lipid content was assessed by analytical thin layer chromatography and flame ionization detection. Binding of NSP4 to various cell lines was measured using a flow cytometric-based assay. Results Secreted NSP4 formed oligomers that contained phospholipid but dissociated to a dimeric species in the presence of non-ionic detergent. The purified glycoprotein binds to the surface of various non-infected cells of distinct lineage. Binding of NSP4 to HT-29, a cell line of intestinal origin, is saturable and independent of divalent cations. Complementary biochemical approaches reveal that NSP4 binds to sulfated glycosaminoglycans on the plasma membrane. Conclusion Our study is the first to analyze an authentic (i.e. non-recombinant) form of NSP4 that is secreted from virus-infected cells. Despite retention of the transmembrane domain, secreted NSP4 remains soluble in an aqueous environment as an oligomeric lipoprotein that can bind to various cell types via an interaction with glycosaminoglycans. This broad cellular tropism exhibited by NSP4 may have implications for the pathophysiology of rotavirus disease.
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Affiliation(s)
- Alicia Didsbury
- School of Biological Sciences, University of Auckland, New Zealand
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15
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Chacko AR, Jeyakanthan J, Ueno G, Sekar K, Rao CD, Dodson EJ, Suguna K, Read RJ. A new pentameric structure of rotavirus NSP4 revealed by molecular replacement. ACTA CRYSTALLOGRAPHICA SECTION D: BIOLOGICAL CRYSTALLOGRAPHY 2011; 68:57-61. [DOI: 10.1107/s0907444911049705] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/04/2011] [Accepted: 11/21/2011] [Indexed: 11/10/2022]
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16
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Asano KM, Gregori F, Souza SP, Rotava D, Oliveira RN, Villarreal LYB, Richtzenhain LJ, Brandão PE. Bovine Rotavirus in Turkeys with Enteritis. Avian Dis 2011; 55:697-700. [DOI: 10.1637/9765-041911-resnote.1] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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17
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Yang W, McCrae MA. The molecular biology of rotaviruses X: intercellular dissemination of rotavirus NSP4 requires glycosylation and is mediated by direct cell-cell contact through cytoplasmic extrusions. Arch Virol 2011; 157:305-14. [DOI: 10.1007/s00705-011-1174-x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2011] [Accepted: 11/08/2011] [Indexed: 01/11/2023]
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18
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Yang W, McCrae MA. The rotavirus enterotoxin (NSP4) promotes re-modeling of the intracellular microtubule network. Virus Res 2011; 163:269-74. [PMID: 22036730 DOI: 10.1016/j.virusres.2011.10.011] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2011] [Revised: 10/14/2011] [Accepted: 10/15/2011] [Indexed: 01/07/2023]
Abstract
Expression of the rotavirus enterotoxin (NSP4) in transfected monkey kidney cells was found to result in a dramatic re-modeling of the microtubule (MT) network. This important centrosome organized cytoskeletal element was dissolved by expression of NSP4 and re-formed in a ring array at the periphery of the cell, similar to that seen following normal virus infection. Site directed mutagenesis of the N-linked glycosylation sites in NSP4 was employed to show that glycosylation of NSP4 was not required for it to promote changes in the MT network. This result together with experiments using conventional inhibitors indicated that NSP4's ability to cause elevation of intracellular calcium levels was also not necessary to effect the changes in the MT network. Use of the centrosome function inhibitor nocodazole demonstrated that NSP4 based remodeling of the MT network was dominant over the normal organizational role of the centrosome. Finally the remodeling of the MT network was shown not to be linked to cellular apoptosis or necrosis. The potential importance of this newly recognised role for NSP4 in the overall process of intracellular pathogenesis by rotaviruses is discussed.
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Affiliation(s)
- Weiming Yang
- School of Life Sciences, University of Warwick, Coventry CV4 7AL, UK
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Novel pentameric structure of the diarrhea-inducing region of the rotavirus enterotoxigenic protein NSP4. J Virol 2011; 85:12721-32. [PMID: 21917949 DOI: 10.1128/jvi.00349-11] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
A novel pentameric structure which differs from the previously reported tetrameric form of the diarrhea-inducing region of the rotavirus enterotoxin NSP4 is reported here. A significant feature of this pentameric form is the absence of the calcium ion located in the core region of the tetrameric structures. The lysis of cells, the crystallization of the region spanning residues 95 to 146 of NSP4 (NSP4(95-146)) of strain ST3 (ST3:NSP4(95-146)) at acidic pH, and comparative studies of the recombinant purified peptide under different conditions by size-exclusion chromatography (SEC) and of the crystal structures suggested pH-, Ca(2+)-, and protein concentration-dependent oligomeric transitions in the peptide. Since the NSP4(95-146) mutant lacks the N-terminal amphipathic domain (AD) and most of the C-terminal flexible region (FR), to demonstrate that the pentameric transition is not a consequence of the lack of the N- and C-terminal regions, glutaraldehyde cross-linking of the ΔN72 and ΔN94 mutant proteins, which contain or lack the AD, respectively, but possess the complete C-terminal FR, was carried out. The results indicate the presence of pentamers in preparations of these longer mutants. Detailed SEC analyses of ΔN94 prepared under different conditions, however, revealed protein concentration-dependent but metal ion- and pH-independent pentamer accumulation at high concentrations which dissociated into tetramers and lower oligomers at low protein concentrations. While calcium appeared to stabilize the tetramer, magnesium in particular stabilized the dimer. ΔN72 existed primarily in the multimeric form under all conditions. These findings of a calcium-free NSP4 pentamer and its concentration-dependent and largely calcium-independent oligomeric transitions open up a new dimension in an understanding of the structural basis of its multitude of functions.
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Gibbons TF, Storey SM, Williams CV, McIntosh A, Mitchel DM, Parr RD, Schroeder ME, Schroeder F, Ball JM. Rotavirus NSP4: Cell type-dependent transport kinetics to the exofacial plasma membrane and release from intact infected cells. Virol J 2011; 8:278. [PMID: 21645398 PMCID: PMC3129587 DOI: 10.1186/1743-422x-8-278] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2011] [Accepted: 06/06/2011] [Indexed: 11/10/2022] Open
Abstract
Background Rotavirus NSP4 localizes to multiple intracellular sites and is multifunctional, contributing to RV morphogenesis, replication and pathogenesis. One function of NSP4 is the induction of early secretory diarrhea by binding surface receptors to initiate signaling events. The aims of this study were to determine the transport kinetics of NSP4 to the exofacial plasma membrane (PM), the subsequent release from intact infected cells, and rebinding to naïve and/or neighboring cells in two cell types. Methods Transport kinetics was evaluated using surface-specific biotinylation/streptavidin pull-downs and exofacial exposure of NSP4 was confirmed by antibody binding to intact cells, and fluorescent resonant energy transfer. Transfected cells similarly were monitored to discern NSP4 movement in the absence of infection or other viral proteins. Endoglycosidase H digestions, preparation of CY3- or CY5- labeled F(ab)2 fragments, confocal imaging, and determination of preferential polarized transport employed standard laboratory techniques. Mock-infected, mock-biotinylated and non-specific antibodies served as controls. Results Only full-length (FL), endoglycosidase-sensitive NSP4 was detected on the exofacial surface of two cell types, whereas the corresponding cell lysates showed multiple glycosylated forms. The C-terminus of FL NSP4 was detected on exofacial-membrane surfaces at different times in different cell types prior to its release into culture media. Transport to the PM was rapid and distinct yet FL NSP4 was secreted from both cell types at a time similar to the release of virus. NSP4-containing, clarified media from both cells bound surface molecules of naïve cells, and imaging showed secreted NSP4 from one or more infected cells bound neighboring cell membranes in culture. Preferential sorting to apical or basolateral membranes also was distinct in different polarized cells. Conclusions The intracellular transport of NSP4 to the PM, translocation across the PM, exposure of the C-terminus on the cell surface and subsequent secretion occurs via an unusual, complex and likely cell-dependent process. The exofacial exposure of the C-terminus poses several questions and suggests an atypical mechanism by which NSP4 traverses the PM and interacts with membrane lipids. Mechanistic details of the unconventional trafficking of NSP4, interactions with host-cell specific molecules and subsequent release require additional study.
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Affiliation(s)
- Thomas F Gibbons
- Department of Pathobiology Texas A&M University, TVMC, College Station, TX 77843-4467, USA
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21
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Rotavirus disrupts calcium homeostasis by NSP4 viroporin activity. mBio 2010; 1. [PMID: 21151776 PMCID: PMC2999940 DOI: 10.1128/mbio.00265-10] [Citation(s) in RCA: 98] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2010] [Accepted: 10/27/2010] [Indexed: 12/22/2022] Open
Abstract
Many viruses alter intracellular calcium homeostasis. The rotavirus nonstructural protein 4 (NSP4), an endoplasmic reticulum (ER) transmembrane glycoprotein, increases intracellular levels of cytoplasmic Ca2+ ([Ca2+]cyto) through a phospholipase C-independent pathway, which is required for virus replication and morphogenesis. However, the NSP4 domain and mechanism that increases [Ca2+]cyto are unknown. We identified an NSP4 domain (amino acids [aa] 47 to 90) that inserts into membranes and has structural characteristics of viroporins, a class of small hydrophobic viral proteins that disrupt membrane integrity and ion homeostasis to facilitate virus entry, assembly, or release. Mutational analysis showed that NSP4 viroporin activity was mediated by an amphipathic α-helical domain downstream of a conserved lysine cluster. The lysine cluster directed integral membrane insertion of the viroporin domain and was critical for viroporin activity. In epithelial cells, expression of wild-type NSP4 increased the levels of free cytoplasmic Ca2+ by 3.7-fold, but NSP4 viroporin mutants maintained low levels of [Ca2+]cyto, were retained in the ER, and failed to form cytoplasmic vesicular structures, called puncta, which surround viral replication and assembly sites in rotavirus-infected cells. When [Ca2+]cyto was increased pharmacologically with thapsigargin, viroporin mutants formed puncta, showing that elevation of calcium levels and puncta formation are distinct functions of NSP4 and indicating that NSP4 directly or indirectly responds to elevated cytoplasmic calcium levels. NSP4 viroporin activity establishes the mechanism for NSP4-mediated elevation of [Ca2+]cyto, a critical event that regulates rotavirus replication and virion assembly. Rotavirus is the leading cause of viral gastroenteritis in children and young animals. Rotavirus infection and expression of nonstructural protein 4 (NSP4) alone dramatically increase cytosolic calcium, which is essential for replication and assembly of infectious virions. This work identifies the intracellular mechanism by which NSP4 disrupts calcium homeostasis by showing that NSP4 is a viroporin, a class of virus-encoded transmembrane pores. Mutational analyses identified residues critical for viroporin activity. Viroporin mutants did not elevate the levels of cytoplasmic calcium in mammalian cells and were maintained in the endoplasmic reticulum rather than forming punctate vesicular structures that are critical for virus replication and morphogenesis. Pharmacological elevation of cytoplasmic calcium levels rescued puncta formation in viroporin mutants, demonstrating that elevation of calcium levels and puncta formation are distinct NSP4 functions. While viroporins typically function in virus entry or release, elevation of calcium levels by NSP4 viroporin activity may serve as a regulatory function to facilitate virus replication and assembly.
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Toxin mediated diarrhea in the 21 century: the pathophysiology of intestinal ion transport in the course of ETEC, V. cholerae and rotavirus infection. Toxins (Basel) 2010; 2:2132-57. [PMID: 22069677 PMCID: PMC3153279 DOI: 10.3390/toxins2082132] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2010] [Accepted: 08/09/2010] [Indexed: 12/31/2022] Open
Abstract
An estimated 4 billion episodes of diarrhea occur each year. As a result, 2–3 million children and 0.5–1 million adults succumb to the consequences of this major healthcare concern. The majority of these deaths can be attributed to toxin mediated diarrhea by infectious agents, such as E. coli, V. cholerae or Rotavirus. Our understanding of the pathophysiological processes underlying these infectious diseases has notably improved over the last years. This review will focus on the cellular mechanism of action of the most common enterotoxins and the latest specific therapeutic approaches that have been developed to contain their lethal effects.
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Abstract
Studies on the molecular biology of rotavirus, the major etiologic agent of gastroenteritis in infants and young children worldwide, have so far led to a large but not exhaustive knowledge of the mechanisms by which rotavirus replicates in the host cell. While the role of rotavirus structural proteins in the replication cycle is well defined, the functions of nonstructural proteins remain poorly understood. Recent experiments of RNA interference have clearly indicated the phases of the replication cycle for which the nonstructural proteins are essentially required. In addition, biochemical studies of their interactions with other viral proteins, together with immunofluorescence experiments on cells expressing recombinant proteins in different combinations, are providing new indications of their functions. This article contains a critical collection of the most recent achievements and the current hypotheses about the roles of nonstructural proteins in virus replication.
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Affiliation(s)
- Francesca Arnoldi
- International Centre for Genetic Engineering & Biotechnology (ICGEB), Padriciano 99, 34012 Trieste, Italy
| | - Oscar R Burrone
- International Centre for Genetic Engineering & Biotechnology (ICGEB), Padriciano 99, 34012 Trieste, Italy
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24
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Díaz Y, Chemello ME, Peña F, Aristimuño OC, Zambrano JL, Rojas H, Bartoli F, Salazar L, Chwetzoff S, Sapin C, Trugnan G, Michelangeli F, Ruiz MC. Expression of nonstructural rotavirus protein NSP4 mimics Ca2+ homeostasis changes induced by rotavirus infection in cultured cells. J Virol 2008; 82:11331-43. [PMID: 18787006 PMCID: PMC2573286 DOI: 10.1128/jvi.00577-08] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2008] [Accepted: 07/28/2008] [Indexed: 12/22/2022] Open
Abstract
Rotavirus infection modifies Ca(2+) homeostasis, provoking an increase in Ca(2+) permeation, the cytoplasmic Ca(2+) concentration ([Ca(2+)](cyto)), and total Ca(2+) pools and a decrease in Ca(2+) response to agonists. A glycosylated viral protein(s), NSP4 and/or VP7, may be responsible for these effects. HT29 or Cos-7 cells were infected by the SA11 clone 28 strain, in which VP7 is not glycosylated, or transiently transfected with plasmids coding for NSP4-enhanced green fluorescent protein (EGFP) or NSP4. The permeability of the plasma membrane to Ca(2+) and the amount of Ca(2+) sequestered in the endoplasmic reticulum released by carbachol or ATP were measured in fura-2-loaded cells at the single-cell level under a fluorescence microscope or in cell suspensions in a fluorimeter. Total cell Ca(2+) pools were evaluated as (45)Ca(2+) uptake. Infection with SA11 clone 28 induced an increase in Ca(2+) permeability and (45)Ca(2+) uptake similar to that found with the normally glycosylated SA11 strain. These effects were inhibited by tunicamycin, indicating that inhibition of glycosylation of a viral protein other than VP7 affects the changes of Ca(2+) homeostasis induced by infection. Expression of NSP4-EGFP or NSP4 in transfected cells induced the same changes observed with rotavirus infection, whereas the expression of EGFP or EGFP-VP4 showed the behavior of uninfected and untransfected cells. Increased (45)Ca(2+) uptake was also observed in cells expressing NSP4-EGFP or NSP4, as evidenced in rotavirus infection. These results indicate that glycosylated NSP4 is primarily responsible for altering the Ca(2+) homeostasis of infected cells through an initial increase of cell membrane permeability to Ca(2+).
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Affiliation(s)
- Yuleima Díaz
- Laboratorio de Fisiología Gastrointestinal, IVIC, Caracas 1020A, Venezuela
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25
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Rajasekaran D, Sastri NP, Marathahalli JR, Indi SS, Pamidimukkala K, Suguna K, Rao CD. The flexible C terminus of the rotavirus non-structural protein NSP4 is an important determinant of its biological properties. J Gen Virol 2008; 89:1485-1496. [PMID: 18474565 DOI: 10.1099/vir.0.83617-0] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
The rotavirus non-structural protein NSP4 functions as the viral enterotoxin and intracellular receptor for the double-layered particles (DLP). The full-length protein cannot be expressed and/or purified to homogeneity from bacterial or insect cells. However, a bacterially expressed and purified mutant lacking the N-terminal 72 aa (DeltaN72) was recently obtained from strains Hg18 and SA11 exhibiting approximately 17-20-, 150-200- and 13166-15800-fold lower DD50 (50% diarrhoea-inducing dose) values in suckling mice compared with that reported for the partially pure, full-length protein, a C-terminal M175I mutant and a synthetic peptide comprising aa 114-135, respectively, suggesting the requirement for a unique conformation for optimal functions of the purified protein. The stretch of approximately 40 aa from the C terminus of the cytoplasmic tail of the endoplasmic reticulum-anchored NSP4 is highly flexible and exhibits high sequence variation compared with the other regions, the significance of which in diarrhoea induction remain unresolved. Here, it was shown that every amino acid substitution or deletion in the flexible C terminus resulted in altered conformation, multimerization, trypsin resistance and thioflavin T (ThT) binding, and affected DLP binding and the diarrhoea-inducing ability of the highly diarrhoeagenic SA11 and Hg18 DeltaN72 in suckling mice. These studies further revealed that high ThT fluorescence correlated with efficient diarrhoea induction, suggesting the importance of an optimal ThT-recognizable conformation in diarrhoea induction by purified NSP4. These results based on biological properties provide a possible conformational basis for understanding the influence of primary sequence variations on diarrhoea induction in newborn mice by purified NSP4s that cannot be explained by extensive sequence analyses.
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Affiliation(s)
- Deepa Rajasekaran
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560012, India.,Department of Microbiology & Cell Biology, Indian Institute of Science, Bangalore 560012, India
| | - Narayan P Sastri
- Department of Microbiology & Cell Biology, Indian Institute of Science, Bangalore 560012, India
| | | | - Shanthinath S Indi
- Department of Microbiology & Cell Biology, Indian Institute of Science, Bangalore 560012, India
| | | | - Kaza Suguna
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560012, India
| | - C Durga Rao
- Department of Microbiology & Cell Biology, Indian Institute of Science, Bangalore 560012, India
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Endoplasmic reticulum chaperones are involved in the morphogenesis of rotavirus infectious particles. J Virol 2008; 82:5368-80. [PMID: 18385250 DOI: 10.1128/jvi.02751-07] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
The final assembly of rotavirus particles takes place in the endoplasmic reticulum (ER). In this work, we evaluated by RNA interference the relevance to rotavirus assembly and infectivity of grp78, protein disulfide isomerase (PDI), grp94, calnexin, calreticulin, and ERp57, members of the two ER folding systems described herein. Silencing the expression of grp94 and Erp57 had no effect on rotavirus infectivity, while knocking down the expression of any of the other four chaperons caused a reduction in the yield of infectious virus of about 50%. In grp78-silenced cells, the maturation of the oligosaccharide chains of NSP4 was retarded. In cells with reduced levels of calnexin, the oxidative folding of VP7 was impaired and the trimming of NSP4 was accelerated, and in calreticulin-silenced cells, the formation of disulfide bonds of VP7 was also accelerated. The knockdown of PDI impaired the formation and/or rearrangement of the VP7 disulfide bonds. All these conditions also affected the correct assembly of virus particles, since compared with virions from control cells, they showed an altered susceptibility to EGTA and heat treatments, a decreased specific infectivity, and a diminished reactivity to VP7 with monoclonal antibody M60, which recognizes only this protein when its disulfide bonds have been correctly formed. In the case of grp78-silenced cells, the virus produced bound less efficiently to MA104 cells than virus obtained from control cells. All these results suggest that these chaperones are involved in the quality control of rotavirus morphogenesis. The complexity of the steps of rotavirus assembly that occur in the ER provide a useful model for studying the organization and operation of the complex network of chaperones involved in maintaining the quality control of this organelle.
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27
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Ruiz MC, Aristimuño OC, Díaz Y, Peña F, Chemello ME, Rojas H, Ludert JE, Michelangeli F. Intracellular disassembly of infectious rotavirus particles by depletion of Ca2+ sequestered in the endoplasmic reticulum at the end of virus cycle. Virus Res 2007; 130:140-50. [PMID: 17643542 DOI: 10.1016/j.virusres.2007.06.005] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2006] [Revised: 05/31/2007] [Accepted: 06/11/2007] [Indexed: 01/24/2023]
Abstract
Rotavirus infection is characterized by a number of Ca(2+) dependent virus-cell interactions. The structure of rotavirus triple-layered particles (TLP) is dependent on Ca(2+) concentration. Acquisition of the capsid outer layer requires a high Ca(2+) concentration inside the ER. Infection modifies Ca(2+) homeostasis of the cell, increasing ER Ca(2+) content, which may be advantageous to virus replication. We studied the role of sequestered Ca(2+) on the stabilization of already mature viral particles within the ER. Thapsigargin (TG), a SERCA pump inhibitor, added for 30min at the end of infection depleted ER Ca(2+) and reduced the titer of already mature TLP accumulated in the cell. Another inhibitor, cyclopiazonic acid, and two Ca(2+) ionophores (A23187 and ionomycin) in the presence of EGTA had similar effects. TG eliminated the peak of radiolabeled TLP, increasing that of DLP in CsCl gradients. Electron microscopy revealed accumulation of clustered particles in the ER, which had lost their integrity. The [Ca(2+)] in the ER of infected cells is important for virus maturation and for maintaining the integrity of mature TLP. Viral particles in this compartment may be potentially infectious, already containing VP7 and VP4.
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Affiliation(s)
- Marie Christine Ruiz
- Laboratorio de Fisiología Gastrointestinal, Instituto Venezolano de Investigaciones Científicas, Caracas 1020A, Venezuela.
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28
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Storey SM, Gibbons TF, Williams CV, Parr RD, Schroeder F, Ball JM. Full-length, glycosylated NSP4 is localized to plasma membrane caveolae by a novel raft isolation technique. J Virol 2007; 81:5472-83. [PMID: 17376898 PMCID: PMC1900257 DOI: 10.1128/jvi.01862-06] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2006] [Accepted: 03/16/2007] [Indexed: 12/12/2022] Open
Abstract
Rotavirus NSP4, initially characterized as an endoplasmic reticulum intracellular receptor, is a multifunctional viral enterotoxin that induces diarrhea in murine pups. There have been recent reports of the secretion of a cleaved NSP4 fragment (residues 112 to 175) and of the association of NSP4 with LC3-positive autophagosomes, raft membranes, and microtubules. To determine if NSP4 traffics to a specific subset of rafts at the plasma membrane, we isolated caveolae from plasma membrane-enriched material that yielded caveola membranes free of endoplasmic reticulum and nonraft plasma membrane markers. Analyses of the newly isolated caveolae from rotavirus-infected MDCK cells revealed full-length, high-mannose glycosylated NSP4. The lack of Golgi network-specific processing of the caveolar NSP4 glycans supports studies showing that NSP4 bypasses the Golgi apparatus. Confocal imaging showed the colocalization of NSP4 with caveolin-1 early and late in infection, elucidating the temporal and spatial NSP4-caveolin-1 association during infection. These data were extended with fluorescent resonance energy transfer analyses that confirmed the NSP4 and caveolin-1 interaction in that the specific fluorescently tagged antibodies were within 10 nm of each other during infection. Cells transfected with NSP4 showed patterns of staining and colocalization with caveolin-1 similar to those of infected cells. This study presents an endoplasmic reticulum contaminant-free caveola isolation protocol; describes the presence of full-length, endoglycosidase H-sensitive NSP4 in plasma membrane caveolae; provides confirmation of the NSP4-caveolin interaction in the presence and absence of other viral proteins; and provides a final plasma membrane destination for Golgi network-bypassing NSP4 transport.
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Affiliation(s)
- Stephen M Storey
- Department of Pathobiology, TVMC, Texas A and M University, TAMU 4467, College Station, TX 77843-4467, USA
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29
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Mir KD, Parr RD, Schroeder F, Ball JM. Rotavirus NSP4 interacts with both the amino- and carboxyl-termini of caveolin-1. Virus Res 2007; 126:106-15. [PMID: 17379346 PMCID: PMC1978065 DOI: 10.1016/j.virusres.2007.02.004] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2006] [Revised: 01/29/2007] [Accepted: 02/05/2007] [Indexed: 11/25/2022]
Abstract
Rotavirus NSP4 plays multiple roles in viral pathogenesis, morphogenesis and replication. We previously reported a direct interaction between full-length NSP4 and the enterotoxic peptide composed of NSP4 residues 114-135 with full-length caveolin-1, the structural protein of caveolae. Caveolin-1 forms a hairpin loop in the cytoplasmic leaflet of plasma membrane caveolae. This unique orientation results in both termini of caveolin-1 exposed to the cytoplasm. The goal of this study was to map the caveolin-1 residues that interact with NSP4 to obtain a more complete picture of this binding event. Utilizing reverse yeast two-hybrid analyses and direct peptide binding assays, the NSP4 binding site was localized to caveolin-1 residues 2-22 and 161-178, at the amino- and carboxyl-termini, respectively. However, NSP4 binding to one of the termini was sufficient for the interaction.
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Affiliation(s)
- Kiran D. Mir
- Texas A&M University, College of Veterinary Medicine and Biomedical Sciences, Department of Pathobiology, College Station, TX 77843
| | - Rebecca D. Parr
- Texas A&M University, College of Veterinary Medicine and Biomedical Sciences, Department of Pathobiology, College Station, TX 77843
| | - Friedhelm Schroeder
- Texas A&M University, College of Veterinary Medicine and Biomedical Sciences, Department of Physiology and Pharmacology, College Station, TX 77843
| | - Judith M. Ball
- Texas A&M University, College of Veterinary Medicine and Biomedical Sciences, Department of Pathobiology, College Station, TX 77843
- *corresponding author Phone: (979) 845-9710, Fax: (979) 845-9231, , Texas A&M University, TVMC, TAMU 4467, College Station, TX 77843
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Bugarcic A, Taylor JA. Rotavirus nonstructural glycoprotein NSP4 is secreted from the apical surfaces of polarized epithelial cells. J Virol 2006; 80:12343-9. [PMID: 17035333 PMCID: PMC1676281 DOI: 10.1128/jvi.01378-06] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
NSP4, a nonstructural glycoprotein encoded by rotavirus, is involved in the morphogenesis of virus particles in the endoplasmic reticulum of infected cells. NSP4 is also implicated in the pathophysiology of rotavirus-induced diarrhea by acting as an enterotoxin. To mediate enterotoxic effects in vivo, NSP4 must be secreted or released from rotavirus-infected cells in a soluble form; however, previous studies have indicated that NSP4 is a transmembrane glycoprotein localized within endomembrane compartments in infected cells. In this study, we examined the fate of NSP4 synthesized in Caco-2 cells infected with bovine rotavirus. Our studies reveal that NSP4 is actively secreted into the culture medium, preferentially from the infected-cell apical surface. The secretion of NSP4 is dramatically inhibited by brefeldin A and monensin, suggesting that a Golgi-dependent pathway is involved in release of the protein. In agreement with the proposed involvement of the Golgi apparatus during secretion, secreted NSP4 appears to undergo additional posttranslational modification compared to its cell-associated counterpart and is partially resistant to deglycosylation by endoglycosidase H. Our experiments identify a novel, soluble form of NSP4 secreted from virus-infected cells with the potential to carry out the enterotoxigenic role previously attributed to recombinant forms of the protein.
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Affiliation(s)
- Andrea Bugarcic
- School of Biological Sciences, University of Auckland, Private Bag 92019, Auckland, New Zealand
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31
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Silvestri LS, Tortorici MA, Vasquez-Del Carpio R, Patton JT. Rotavirus glycoprotein NSP4 is a modulator of viral transcription in the infected cell. J Virol 2006; 79:15165-74. [PMID: 16306588 PMCID: PMC1316041 DOI: 10.1128/jvi.79.24.15165-15174.2005] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
The outer shell of the rotavirus triple-layered virion is lost during cell entry, yielding a double-layered particle (DLP) that directs synthesis of viral plus-strand RNAs. The plus-strand RNAs act as templates for synthesis of the segmented double-stranded RNA (dsRNA) genome in viral inclusion bodies (viroplasms). The viral endoplasmic reticulum (ER)-resident glycoprotein NSP4 recruits progeny DLPs formed in viroplasms to the ER, where the particles are converted to triple-layered particles (TLPs) via budding. In this study, we have used short interfering RNAs to probe the role of NSP4 in the viral life cycle. Our analysis showed that knockdown of NSP4 expression had no marked effect on the expression of other viral proteins or on the replication of the dsRNA genome segments. However, NSP4 loss of function suppressed viroplasm maturation and caused a maldistribution of nonstructural and structural proteins that normally accumulate in viroplasms. NSP4 loss of function also inhibited formation of packaged virus particles, instead inducing the accumulation of empty particles. Most significant was the observation that NSP4 knockdown led to dramatically increased levels of viral transcription late in the infection cycle. These findings point to a multifaceted role for NSP4 in virus replication, including influencing the development of viroplasms, linking genome packaging with particle assembly, and acting as a modulator of viral transcription. By recruiting transcriptionally active or potentially active DLPs to the ER for conversion to quiescent TLPs, NSP4 acts as a feedback inhibitor down-regulating viral transcription when adequate levels of plus-strand RNAs are available to allow for productive infection.
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Affiliation(s)
- Lynn S Silvestri
- Laboratory of Infectious Diseases, NIAID, National Institutes of Health, 50 South Dr., MSC 8026, Room 6314, Bethesda, MD 20892-8026, USA
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32
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Parr RD, Storey SM, Mitchell DM, McIntosh AL, Zhou M, Mir KD, Ball JM. The rotavirus enterotoxin NSP4 directly interacts with the caveolar structural protein caveolin-1. J Virol 2006; 80:2842-54. [PMID: 16501093 PMCID: PMC1395425 DOI: 10.1128/jvi.80.6.2842-2854.2006] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2005] [Accepted: 12/13/2005] [Indexed: 11/20/2022] Open
Abstract
Rotavirus nonstructural protein 4 (NSP4) is known to function as an intracellular receptor at the endoplasmic reticulum (ER) critical to viral morphogenesis and is the first characterized viral enterotoxin. Exogenously added NSP4 induces diarrhea in rodent pups and stimulates secretory chloride currents across intestinal segments as measured in Ussing chambers. Circular dichroism studies further reveal that intact NSP4 and the enterotoxic peptide (NSP4(114-135)) that is located within the extended, C-terminal amphipathic helix preferentially interact with caveola-like model membranes. We now show colocalization of NSP4 and caveolin-1 in NSP4-transfected and rotavirus-infected mammalian cells in reticular structures surrounding the nucleus (likely ER), in the cytosol, and at the cell periphery by laser scanning confocal microscopy. A direct interaction between NSP4 residues 112 to 140 and caveolin-1 was determined by the Pro-Quest yeast two-hybrid system with full-length NSP4 and seven overlapping deletion mutants as bait, caveolin-1 as prey, and vice versa. Coimmunoprecipitation of NSP4-caveolin-1 complexes from rotavirus-infected mammalian cells demonstrated that the interaction occurs during viral infection. Finally, binding of caveolin-1 from mammalian cell lysates to Sepharose-bound, NSP4-specific synthetic peptides confirmed the yeast two-hybrid data and further delineated the binding domain to amino acids 114 to 135. We propose that the association of NSP4 and caveolin-1 contributes to NSP4 intracellular trafficking from the ER to the cell surface and speculate that exogenously added NSP4 stimulates signaling molecules located in caveola microdomains.
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Affiliation(s)
- Rebecca D Parr
- Department of Pathobiology, Texas A&M University 4467, College Station, Texas 77843, USA
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33
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Cho SL, Ahn JH, Kim K, Chung SI, Lim I, Kim W. Genetic Variation in the NSP4 Gene of Human Rotavirus Isolated in Seoul. ACTA ACUST UNITED AC 2006. [DOI: 10.4167/jbv.2006.36.2.79] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Affiliation(s)
- Sung-Lim Cho
- Department of Microbiology, Chung-Ang University College of Medicine, Seoul 156-756, Korea
| | - Jang-Hoon Ahn
- Department of Microbiology, Chung-Ang University College of Medicine, Seoul 156-756, Korea
| | - Kijeong Kim
- Department of Microbiology, Chung-Ang University College of Medicine, Seoul 156-756, Korea
| | - Sang-In Chung
- Department of Microbiology, Chung-Ang University College of Medicine, Seoul 156-756, Korea
| | - Inseok Lim
- Department of Pediatrics, Chung-Ang University College of Medicine, Seoul 156-756, Korea
| | - Wonyong Kim
- Department of Microbiology, Chung-Ang University College of Medicine, Seoul 156-756, Korea
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34
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Jagannath MR, Kesavulu MM, Deepa R, Sastri PN, Kumar SS, Suguna K, Rao CD. N- and C-terminal cooperation in rotavirus enterotoxin: novel mechanism of modulation of the properties of a multifunctional protein by a structurally and functionally overlapping conformational domain. J Virol 2006; 80:412-25. [PMID: 16352566 PMCID: PMC1317517 DOI: 10.1128/jvi.80.1.412-425.2006] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2005] [Accepted: 10/04/2005] [Indexed: 01/07/2023] Open
Abstract
Rotavirus NSP4 is a multifunctional endoplasmic reticulum (ER)-resident nonstructural protein with the N terminus anchored in the ER and about 131 amino acids (aa) of the C-terminal tail (CT) oriented in the cytoplasm. Previous studies showed a peptide spanning aa 114 to 135 to induce diarrhea in newborn mouse pups with the 50% diarrheal dose approximately 100-fold higher than that for the full-length protein, suggesting a role for other regions in the protein in potentiating its diarrhea-inducing ability. In this report, employing a large number of methods and deletion and amino acid substitution mutants, we provide evidence for the cooperation between the extreme C terminus and a putative amphipathic alpha-helix located between aa 73 and 85 (AAH73-85) at the N terminus of DeltaN72, a mutant that lacked the N-terminal 72 aa of nonstructural protein 4 (NSP4) from Hg18 and SA11. Cooperation between the two termini appears to generate a unique conformational state, specifically recognized by thioflavin T, that promoted efficient multimerization of the oligomer into high-molecular-mass soluble complexes and dramatically enhanced resistance against trypsin digestion, enterotoxin activity of the diarrhea-inducing region (DIR), and double-layered particle-binding activity of the protein. Mutations in either the C terminus, AAH73-85, or the DIR resulted in severely compromised biological functions, suggesting that the properties of NSP4 are subject to modulation by a single and/or overlapping highly sensitive conformational domain that appears to encompass the entire CT. Our results provide for the first time, in the absence of a three-dimensional structure, a unique conformation-dependent mechanism for understanding the NSP4-mediated pleiotropic properties including virus virulence and morphogenesis.
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Affiliation(s)
- M R Jagannath
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore 560012, India
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35
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Guzman E, McCrae MA. Molecular characterization of the rotavirus NSP4 enterotoxin homologue from group B rotavirus. Virus Res 2005; 110:151-60. [PMID: 15845266 DOI: 10.1016/j.virusres.2005.02.005] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2004] [Revised: 02/14/2005] [Accepted: 02/14/2005] [Indexed: 11/26/2022]
Abstract
The RNA segment (Gene 10) from a human group B rotavirus which encodes the homologue of the rotavirus enterotoxin (NSP4) has been cloned and sequenced. The gene is of the same length (751 nucleotides) as its better-characterized group A rotavirus counterpart but shows minimal homology (approximately 10%) to it at the primary sequence level. Despite this low level of sequence homology, secondary structure predictions for the group B protein (ADRV-NSP4) showed a close similarity of structural features with the group A protein. Full-length ADRV-NSP4 was expressed in Escherichia coli with an amino terminal 6xHis tag that was used to purify it to homogeneity. The cytotoxicity of the purified protein was examined in a rapid dye-uptake assay that assesses membrane permeability and was found to be comparable to its group A counterpart.
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Affiliation(s)
- E Guzman
- Department of Biological Sciences, University of Warwick, Gibbet Hill Rd, Coventry CV4 7AL, UK
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36
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Ball JM, Mitchell DM, Gibbons TF, Parr RD. Rotavirus NSP4: a multifunctional viral enterotoxin. Viral Immunol 2005; 18:27-40. [PMID: 15802952 DOI: 10.1089/vim.2005.18.27] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Affiliation(s)
- Judith M Ball
- Department of Pathobiology, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, 4467 TAMU, College Station, TX 77843, USA.
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37
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Ishino M, Mise K, Takemura H, Ahmed MU, Alam MM, Naik TN, Kobayashi N. Comparison of NSP4 protein between group A and B human rotaviruses: detection of novel diarrhea-causing sequences in group B NSP4. Arch Virol 2005; 151:173-82. [PMID: 16132179 DOI: 10.1007/s00705-005-0616-8] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2005] [Accepted: 07/04/2005] [Indexed: 11/27/2022]
Abstract
The human group B rotavirus is a causative agent of severe adult diarrhea. In this study, we analyzed the NSP4 structure of a group B rotavirus strain, CAL-1, and determined whether enterotoxin activity was present in CAL-1 NSP4. CAL-1 NSP4 was comprised of 219 amino acids which was longer than group A and C rotavirus NSP4, and the primary structures of their sequences differed considerably. However, CAL-1 NSP4 had an enterotoxin-like sequence (residues 106-127) that was only 27% identical to the enterotoxin region of NSP4 of KUN (a group A rotavirus strain) at residues 114-135. Interestingly, both of the synthetic peptides, one (residues 99-128) containing the enterotoxin-like sequence and the other (residues 191-219) containing 29 C-terminal amino acids of CAL-1 NSP4, induced diarrhea in 5.5-day-old mice, but not in 17.5-day-old mice, when administered parenterally. Thus, rotavirus "enterotoxin" sequences could be considerably divergent.
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Affiliation(s)
- M Ishino
- Department of Hygiene, Sapporo Medical University, Sapporo, Japan.
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38
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López T, Camacho M, Zayas M, Nájera R, Sánchez R, Arias CF, López S. Silencing the morphogenesis of rotavirus. J Virol 2005; 79:184-92. [PMID: 15596814 PMCID: PMC538724 DOI: 10.1128/jvi.79.1.184-192.2005] [Citation(s) in RCA: 102] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
The morphogenesis of rotaviruses follows a unique pathway in which immature double-layered particles (DLPs) assembled in the cytoplasm bud across the membrane of the endoplasmic reticulum (ER), acquiring during this process a transient lipid membrane which is modified with the ER resident viral glycoproteins NSP4 and VP7; these enveloped particles also contain VP4. As the particles move towards the interior of the ER cisternae, the transient lipid membrane and the nonstructural protein NSP4 are lost, while the virus surface proteins VP4 and VP7 rearrange to form the outermost virus protein layer, yielding mature infectious triple-layered particles (TLPs). In this work, we have characterized the role of NSP4 and VP7 in rotavirus morphogenesis by silencing the expression of both glycoproteins through RNA interference. Silencing the expression of either NSP4 or VP7 reduced the yield of viral progeny by 75 to 80%, although the underlying mechanism of this reduction was different in each case. Blocking the synthesis of NSP4 affected the intracellular accumulation and the cellular distribution of several viral proteins, and little or no virus particles (neither DLPs nor TLPs) were assembled. VP7 silencing, in contrast, did not affect the expression or distribution of other viral proteins, but in its absence, enveloped particles accumulated within the lumen of the ER, and no mature infectious virus was produced. Altogether, these results indicate that during a viral infection, NSP4 serves as a receptor for DLPs on the ER membrane and drives the budding of these particles into the ER lumen, while VP7 is required for removing the lipid envelope during the final step of virus morphogenesis.
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Affiliation(s)
- Tomas López
- Departamento de Genética del Desarrollo y Fisiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, Mexico
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39
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Iturriza-Gòmara M, Anderton E, Kang G, Gallimore C, Phillips W, Desselberger U, Gray J. Evidence for genetic linkage between the gene segments encoding NSP4 and VP6 proteins in common and reassortant human rotavirus strains. J Clin Microbiol 2003; 41:3566-73. [PMID: 12904356 PMCID: PMC179808 DOI: 10.1128/jcm.41.8.3566-3573.2003] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
NSP4-encoding genes of 78 human rotavirus strains of common or reassortant genotypes were characterized by reverse transcription-PCR followed by sequencing and phylogenetic analysis. It was found that all the human strains characterized clustered into only two of the five known NSP4 genotypes. Linkage between NSP4 genotypes and VP6 subgroups was 100%, NSP4 genotype A being linked to VP6 of subgroup I (SGI) and NSP4 of genotype B being linked to VP6 of SGII. The diversity among the NSP4- and VP6-encoding genes was significantly less than that among the VP7 and VP4 genes in cocirculating human rotavirus strains. Whereas G and P types appear to be shared among different animal species and humans, the NSP4- and VP6-encoding genes appear to segregate according to their host of origin, suggesting that these two proteins may be host restriction determinants. The NSP4-VP6 association may be structurally determined during rotavirus replication (morphogenesis).
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Affiliation(s)
- Miren Iturriza-Gòmara
- Enteric Virus Unit, Enteric, Respiratory and Neurological Virus Laboratory, Health Protection Agency, London, United Kingdom.
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40
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Berkova Z, Morris AP, Estes MK. Cytoplasmic calcium measurement in rotavirus enterotoxin-enhanced green fluorescent protein (NSP4-EGFP) expressing cells loaded with Fura-2. Cell Calcium 2003; 34:55-68. [PMID: 12767893 DOI: 10.1016/s0143-4160(03)00022-8] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The green fluorescent protein (GFP) and its analogs are standard markers of protein expression and intracellular localization of proteins. The fluorescent properties of GFP complicate accurate measurement of intracellular calcium using calcium sensitive fluorophores, which show a great degree of spectral overlap with GFP, or their K(d) values are too high for accurate measurement of subtle changes in cytoplasmic calcium concentrations. Here we describe a simple modification of the standard microscope-based Fura-2 calcium-imaging technique which permits the quantitative measurement of intracellular calcium levels in cells expressing enhanced green fluorescent protein (EGFP) fusion proteins. Longpass emission filtering of the Fura-2 signal in cells expressing an EGFP fusion protein is sufficient to eliminate the EGFP-Fura-2 emission spectra overlap and allows quantitative calibration of intracellular calcium. To validate this technique, we investigated the ability of rotavirus enterotoxin NSP4-EGFP to elevate intracellular calcium levels in mammalian HEK 293 cells. We show here that inducible intracellular expression of NSP4-EGFP fusion protein elevates basal intracellular calcium more than two-fold by a phospholipase C (PLC) independent mechanism.
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Affiliation(s)
- Z Berkova
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, TX 77030, USA
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41
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Mirazimi A, Magnusson KE, Svensson L. A cytoplasmic region of the NSP4 enterotoxin of rotavirus is involved in retention in the endoplasmic reticulum. J Gen Virol 2003; 84:875-883. [PMID: 12655088 DOI: 10.1099/vir.0.18786-0] [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
The rotavirus genome encodes two glycoproteins, one structural (VP7) and one non-structural (NSP4), both of which mature and remain in the endoplasmic reticulum (ER). While three amino acids in the N terminus have been proposed to function as a retention signal for VP7, no information is yet available on how NSP4 remains associated with the ER. In this study, we have investigated the ER retention motif of NSP4 by producing various C-terminal truncations. Deleting the C terminus by 52 amino acids did not change the intracellular distribution of NSP4, but an additional deletion of 38 amino acids diminished the ER retention and resulted in the expression of NSP4 on the cell surface. Brefeldin A treatment prevented NSP4 from reaching the cell surface, suggesting that C-terminal truncated plasma membrane NSP4 is transported through the normal secretory pathway. On the basis of these results, we propose that the region between amino acids 85 and 123 in the cytoplasmic region of NSP4 are involved in ER retention.
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Affiliation(s)
- Ali Mirazimi
- Department of Virology, Swedish Institute for Infectious Disease Control/Karolinska Institute, 171 82 Solna, Sweden
| | - Karl-Eric Magnusson
- Division of Medical Microbiology, Department of Molecular and Clinical Medicine, University of Linköping, Sweden
| | - Lennart Svensson
- Division of Medical Microbiology, Department of Molecular and Clinical Medicine, University of Linköping, Sweden
- Department of Virology, Swedish Institute for Infectious Disease Control/Karolinska Institute, 171 82 Solna, Sweden
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42
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II, 7. Interaction of the rotavirus nonstructural glycoprotein NSP4 with viral and cellular components. ACTA ACUST UNITED AC 2003. [DOI: 10.1016/s0168-7069(03)09014-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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43
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Mori Y, Borgan MA, Ito N, Sugiyama M, Minamoto N. Sequential analysis of nonstructural protein NSP4s derived from Group A avian rotaviruses. Virus Res 2002; 89:145-51. [PMID: 12367757 DOI: 10.1016/s0168-1702(02)00112-0] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
We determined the NSP4 sequences of turkey rotavirus strains Ty-1 and Ty-3 and a chicken rotavirus, strain Ch-1, and compared these sequences with those of a pigeon rotavirus, strain PO-13, and mammalian rotaviruses. The turkey strains and PO-13 were found to be closely related (90-97% homologies). Ch-1 NSP4 was distinctly different from other avian rotavirus NSP4s, with 78-79% homologies. The NSP4 sequences of avian rotaviruses were found to be 6-7 amino acids shorter than those of all mammalian strains and to have considerably low identities (31-37%) with them. Therefore, it seems highly likely that the NSP4 genes of avian rotaviruses are classified into two NSP4 genotypes distinct from those of mammalian rotaviruses. The enterotoxin domain in NSP4 is conserved in terms of its sequential and structural properties despite extremely low homologies in the full lengths of NSP4s in avian and mammalian rotaviruses.
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Affiliation(s)
- Yoshio Mori
- Department of Veterinary Public Health, Faculty of Agriculture, Gifu University, 1-1 Yanagido, Gifu 501-1193, Japan
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44
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Mori Y, Borgan MA, Ito N, Sugiyama M, Minamoto N. Diarrhea-inducing activity of avian rotavirus NSP4 glycoproteins, which differ greatly from mammalian rotavirus NSP4 glycoproteins in deduced amino acid sequence in suckling mice. J Virol 2002; 76:5829-34. [PMID: 11992013 PMCID: PMC137017 DOI: 10.1128/jvi.76.11.5829-5834.2002] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Avian rotavirus NSP4 glycoproteins expressed in Escherichia coli acted as enterotoxins in suckling mice, as did mammalian rotavirus NSP4 glycoproteins, despite great differences in the amino acid sequences. The enterotoxin domain of PO-13 NSP4 exists in amino acid residues 109 to 135, a region similar to that reported in SA11 NSP4.
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Affiliation(s)
- Yoshio Mori
- Department of Veterinary Public Health, Faculty of Agriculture, Gifu University, Gifu 501-1193, Japan
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45
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Ito H, Sugiyama M, Masubuchi K, Mori Y, Minamoto N. Complete nucleotide sequence of a group A avian rotavirus genome and a comparison with its counterparts of mammalian rotaviruses. Virus Res 2001; 75:123-38. [PMID: 11325467 DOI: 10.1016/s0168-1702(01)00234-9] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
The nucleotide sequences encoding four structural proteins (VP1-4) and six nonstructural proteins (NSP1-6) of avian rotavirus PO-13 were determined. Based on the results of earlier sequencing studies [Ito et al., 1995, Sequence analysis of cDNA for the VP6 protein of group A avian rota viruses. Arch. Vriol. 140, 605-612; Rohwedder et al., 1997, Chicken rotavirus Ch-1 shows a second type of avian VP6 gene, Virus Genes 15, 65-71; Rohwedder et al., 1997, Bovine rotavirus 993/83 shows a third subtype of avian VP7 protein, Virus Genes 14, 147-151], determination of PO-13 genome sequence has been completed. The PO-13 genome is 18845 nucleotides in length. It is 290 nucleotides longer than the genome of SA11. The amino acid sequence homology between PO-13 and mammalian rotaviruses ranged from 76-77% (VP1) to 16-18% (NSP1). The features of gene and amino acid sequence were compared with those of the corresponding protein of mammalian rotaviruses. Based on results of the phylogenetic analyses of NSP1, we speculate that an ancestral rotavirus could have separated into groups A, B and C rotaviruses at an early evolutionary stage and that group A rotavirus separated into mammalian and avian rotaviruses with host evolution.
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Affiliation(s)
- H Ito
- Department of Veterinary Public Health, Faculty of Agriculture, Gifu University, 1-1 Yanagido, 501-1193, Gifu, Japan
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46
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Bowman GD, Nodelman IM, Levy O, Lin SL, Tian P, Zamb TJ, Udem SA, Venkataraghavan B, Schutt CE. Crystal structure of the oligomerization domain of NSP4 from rotavirus reveals a core metal-binding site. J Mol Biol 2000; 304:861-71. [PMID: 11124032 DOI: 10.1006/jmbi.2000.4250] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
During the maturation of rotaviral particles, non-structural protein 4 (NSP4) plays a critical role in the translocation of the immature capsid into the lumen of the endoplasmic reticulum. Full-length NSP4 and a 22 amino acid peptide (NSP4(114-135)) derived from this protein have been shown to induce diarrhea in young mice in an age-dependent manner, and may therefore be the agent responsible for rotavirally-induced symptoms. We have determined the crystal structure of the oligomerization domain of NSP4 which spans residues 95 to 137 (NSP4(95-137)). NSP4(95-137) self-associates into a parallel, tetrameric coiled-coil, with the hydrophobic core interrupted by three polar layers occupying a and d-heptad positions. Side-chains from two consecutive polar layers, consisting of four Gln123 and two of the four Glu120 residues, coordinate a divalent cation. Two independent structures built from MAD-phased data indicated the presence of a strontium and calcium ion bound at this site, respectively. This metal-binding site appears to play an important role in stabilizing the homo-tetramer, which has implications for the engagement of NSP4 as an enterotoxin.
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Affiliation(s)
- G D Bowman
- Department of Molecular Biology, Lewis Thomas Laboratories, Princeton University, Princeton, NJ 08544, USA
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47
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Mirazimi A, Svensson L. ATP is required for correct folding and disulfide bond formation of rotavirus VP7. J Virol 2000; 74:8048-52. [PMID: 10933714 PMCID: PMC112337 DOI: 10.1128/jvi.74.17.8048-8052.2000] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Rotavirus is one of very few viruses that utilize the endoplasmic reticulum (ER) for assembly, and therefore it has been used as an attractive model to study ER-associated protein folding. In this study, we have examined the requirements for metabolic energy (ATP) for correct folding of the luminal and ER-associated VP7 of rotavirus. We found that VP7 rapidly misfolds in an energy-depleted milieu and is not degraded within 60 min. We also found that VP7 attained a stable minimum-energy state soon after translation in the ER. Most surprisingly, energy-misfolded VP7 could be recovered and establish correct disulfide bonds and antigenicity following a shift to an ATP-rich milieu. Using a Semliki Forest virus expression system, we observed that VP7 requires ATP and cellular, but not viral, factors for correct disulfide bond formation. Our results show for the first time that the disulfide bond formation of rotavirus VP7 is an ATP-dependent process. It has previously been shown that chaperones hydrolyze ATP during interaction with newly synthesized polypeptides and prevent nonproductive intra- and intermolecular interactions. The most reasonable explanation for the energy requirement of VP7 is thus a close interaction during folding with an ATP-dependent chaperone, such as BiP (Grp78), and possibly with protein disulfide isomerase. Taken together, our observations provide new information about folding of ER-associated proteins in general and rotavirus VP7 in particular.
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Affiliation(s)
- A Mirazimi
- Department of Virology, Swedish Institute for Infectious Disease Control, Karolinska Institute, 171 82 Solna, Sweden
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Browne EP, Bellamy AR, Taylor JA. Membrane-destabilizing activity of rotavirus NSP4 is mediated by a membrane-proximal amphipathic domain. J Gen Virol 2000; 81:1955-1959. [PMID: 10900033 DOI: 10.1099/0022-1317-81-8-1955] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Expression of the rotavirus non-structural glycoprotein NSP4 in E. coli leads to a decrease in optical density of the culture and release of [(3)H]uridine into the medium, effects attributable to the ability of NSP4 to perturb the bacterial membrane. To identify a domain of NSP4 responsible, different regions of the polypeptide were expressed in E. coli. Membrane destabilization is associated with a region of the protein located within residues 48-91, which includes a potential cationic amphipathic helix. A second region of NSP4 that contains a coiled-coil oligomerization domain and a sequence reported to function as a viral enterotoxin enhances the membrane-destabilizing activity of residues 48-91, but has no direct effect on the membrane stability. These studies suggest that the membrane-destabilizing and enterotoxic properties of NSP4 may be mediated by different regions of the polypeptide and suggest a possible basis for the cytotoxicity of NSP4 in mammalian cells.
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Affiliation(s)
- Edward P Browne
- Microbiology and Virology Research Group, School of Biological Sciences, University of Auckland, Private Bag 92019, Auckland, New Zealand1
| | - A Richard Bellamy
- Microbiology and Virology Research Group, School of Biological Sciences, University of Auckland, Private Bag 92019, Auckland, New Zealand1
| | - John A Taylor
- Microbiology and Virology Research Group, School of Biological Sciences, University of Auckland, Private Bag 92019, Auckland, New Zealand1
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49
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Tian P, Ottaiano A, Reilly PA, Udem S, Zamb T. The authentic sequence of rotavirus SA11 nonstructural protein NSP4. Virus Res 2000; 66:117-22. [PMID: 10725544 DOI: 10.1016/s0168-1702(99)00130-6] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Recent studies demonstrate that the rotavirus nonstructural protein NSP4 functions as an enterotoxin and plays an important role in viral pathogenesis. Previous in vitro studies of NSP4 have used a cDNA clone of gene 10 derived from the prototypic rotavirus strain, SA11. We recently compared the sequence of the commonly used NSP4 cDNA with the sequence obtained from several SA11 isolates by direct sequencing of reverse transcription polymerase chain reaction products. One codon difference was identified between the cDNA clone and the SA11 virus isolates, and this resulted in a predicted amino acid substitution at position 47. The cDNA sequence specifies an asparagine at position 47, and the SA11 virus gene 10 encodes a hisitidine. To determine if this amino acid substitution altered the function of NSP4, we analyzed the ability of both NSP4-Asn47 and NSP4-His47 to regulate intracellular calcium levels and exhibit cell cytotoxicity. Our results indicate that the expression of NSP4-His47 from a recombinant baculovirus displays enhanced cytotoxicity and calcium flux.
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Affiliation(s)
- P Tian
- Viral Vaccine Research, Wyeth-Lederle Vaccines, Building 180/216-16, 401 North Middleton Road, Pearl River, NY 10965, USA.
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50
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Xu A, Bellamy AR, Taylor JA. Expression of translationally controlled tumour protein is regulated by calcium at both the transcriptional and post-transcriptional level. Biochem J 1999; 342 Pt 3:683-9. [PMID: 10477280 PMCID: PMC1220510] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/13/2023]
Abstract
We have investigated how the programme of protein synthesis is altered in response to a loss of calcium homoeostasis in Cos-7 cells using a differential proteome mapping approach. Exposure of the cells to the calcium ionophore A23187 or thapsigargin, or alternatively, expression of a viral glycoprotein reported to deplete intracellular calcium stores, resulted in the up-regulated expression of a characteristic set of proteins. One of these is the translationally controlled tumour protein (TCTP), a cytoplasmic protein whose expression has not previously been linked to calcium perturbation. Quantitative Northern blot assay demonstrated that steady-state mRNA abundance of TCTP was also increased under these conditions. Clamping the cytosolic calcium concentration by the introduction of bis-(o-aminophenoxy)-ethane-N,N,N',N'-tetra-acetic acid (BAPTA) into cells did not affect the increase in steady-state levels of TCTP mRNA observed in response to ionophore. Therefore depletion of endoplasmic reticulum (ER) calcium, but not elevation of the cytosolic calcium concentration, was responsible for increased transcription of the TCTP gene. However, the presence of BAPTA significantly attenuated the ionophore-mediated increase in levels of the protein. Moreover, the level of TCTP in ionophore-treated cells increased in advance of a detectable increase in the corresponding mRNA abundance. These results indicate that expression of TCTP is regulated at two distinct levels in response to the concentration of calcium in different cellular compartments. Whereas depletion of the ER store causes an increase in TCTP mRNA abundance, increased cytosolic calcium concentrations regulate gene expression at the post-transcriptional level.
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Affiliation(s)
- A Xu
- Biochemistry and Molecular Biology Research Group, School of Biological Sciences, University of Auckland, Private Bag 92019, Auckland, New Zealand
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