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Mollik M, Rohorzka A, Chen X, Kropff B, Eisler L, Külekci B, Puchhammer-Stöckl E, Thomas M, Görzer I. Growth defect of domain III glycoprotein B mutants of human cytomegalovirus reverted by compensatory mutations co-localizing in post-fusion conformation. mBio 2024:e0181224. [PMID: 39315800 DOI: 10.1128/mbio.01812-24] [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: 06/19/2024] [Accepted: 08/29/2024] [Indexed: 09/25/2024] Open
Abstract
Cell entry is a crucial step for a virus to infect a host cell. Human cytomegalovirus utilizes glycoprotein B (gB) to fuse the viral and host cell membranes upon receptor binding of gH/gL-containing complexes. Fusion is mediated by major conformational changes of gB from a metastable pre-fusion to a stable post-fusion state whereby the central trimeric coiled-coils, formed by domain (Dom)III α helices, remain structurally nearly unchanged. To better understand the role of the stable core, we individually introduced three potentially helix-breaking or one disulfide bond-breaking mutation in the DIII α3 to study different aspects of the viral behavior upon long-term culturing. Two of the three helix-breaking mutations, gB_Y494P and gB_I495P, were lethal for the virus in either fibroblasts or epithelial cells. The third substitution, gB_G493P, on the other hand, displayed a delayed replication and spread, which was more pronounced in epithelial cells, hinting at an impaired fusion. Interestingly, the disulfide bond-breaker mutation, gB_C507S, performed strikingly differently in the two cell types - lethal in epithelial cells and an atypical phenotype in fibroblasts, respectively. Replication curve analyses paired with the infection efficiency, the spread morphology, and the cell-cell fusogenicity suggest a dysregulated fusion process, which could be reverted by second-site mutations mapping predominantly to gB DomV. Our findings underline the functional importance of a stable DomIII core for a well-regulated DomV rearrangement during fusion.IMPORTANCEHuman cytomegalovirus (HCMV) can establish a lifelong infection. In most people, the infection follows an asymptomatic course; however, it is a major cause of morbidity and mortality in immunocompromised patients or neonates. HCMV has a very broad cell tropism, ranging from fibroblasts to epi- and endothelial cells. The virus uses different entry pathways utilizing the core fusion machinery consisting of glycoprotein complexes gH/gL and glycoprotein B (gB). The fusion protein gB undergoes fundamental rearrangements from a metastable pre-fusion to a stable post-fusion conformation. Here, we characterized the viral behavior after the introduction of four single-point mutations in the gB central core. These led to various cell type-specific atypical phenotypes and the emergence of compensatory mutations, demonstrating an important interaction between domains III and V. We provide a new basis for the development of a structurally and functionally altered gB, which can further serve as a tool for drug and vaccine development.
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Affiliation(s)
- Madlen Mollik
- Center for Virology, Medical University of Vienna, Vienna, Austria
| | - Andreas Rohorzka
- Center for Virology, Medical University of Vienna, Vienna, Austria
| | - Xiaohan Chen
- Virologisches Institut, Klinische und Molekulare Virologie, Friedrich Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany
| | - Barbara Kropff
- Virologisches Institut, Klinische und Molekulare Virologie, Friedrich Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany
| | - Lukas Eisler
- Center for Virology, Medical University of Vienna, Vienna, Austria
| | - Büsra Külekci
- Center for Virology, Medical University of Vienna, Vienna, Austria
| | | | - Marco Thomas
- Virologisches Institut, Klinische und Molekulare Virologie, Friedrich Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany
| | - Irene Görzer
- Center for Virology, Medical University of Vienna, Vienna, Austria
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Fornara C, Schultz E, Lilleri D, Baldanti F, Ryckman B, Gerna G. Fibroblast, Epithelial and Endothelial Cell-Derived Human Cytomegalovirus Strains Display Distinct Neutralizing Antibody Responses and Varying Levels of gH/gL Complexes. Int J Mol Sci 2023; 24:4417. [PMID: 36901847 PMCID: PMC10003051 DOI: 10.3390/ijms24054417] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2022] [Revised: 02/03/2023] [Accepted: 02/16/2023] [Indexed: 02/25/2023] Open
Abstract
In sequential sera from pregnant women with HCMV primary infection (PI), the serum neutralizing activity is higher against virions produced in epithelial and endothelial cells than in fibroblasts. Immunoblotting shows that the pentamer complex/trimer complex (PC/TC) ratio varies according to the producer cell culture type used for the virus preparation to be employed in the neutralizing antibody (NAb) assay, and is lower in fibroblasts and higher in epithelial, and especially endothelial cells. The blocking activity of TC- and PC-specific inhibitors varies according to the PC/TC ratio of virus preparations. The rapid reversion of the virus phenotype following its back passage to the original cell culture (fibroblasts) potentially argues in favor of a producer cell effect on virus phenotype. However, the role of genetic factors cannot be overlooked. In addition to the producer cell type, the PC/TC ratio may differ in single HCMV strains. In conclusion, the NAb activity not only varies with different HCMV strains, but is a dynamic parameter changing according to virus strain, type of target and producer cells, and number of cell culture passages. These findings may have some important implications for the development of both therapeutic antibodies and subunit vaccines.
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Affiliation(s)
- Chiara Fornara
- Microbiology and Virology Unit, Fondazione IRCCS Policlinico San Matteo, 27100 Pavia, Italy
| | - Eric Schultz
- Center for Biomolecular Structure and Dynamics, University of Montana, Missoula, MT 59812, USA
- Division of Biological Sciences, University of Montana, Missoula, MT 59812, USA
| | - Daniele Lilleri
- Microbiology and Virology Unit, Fondazione IRCCS Policlinico San Matteo, 27100 Pavia, Italy
| | - Fausto Baldanti
- Microbiology and Virology Unit, Fondazione IRCCS Policlinico San Matteo, 27100 Pavia, Italy
- Department of Clinical, Surgical, Diagnostic and Pediatric Sciences, University of Pavia, 27100 Pavia, Italy
| | - Brent Ryckman
- Center for Biomolecular Structure and Dynamics, University of Montana, Missoula, MT 59812, USA
- Division of Biological Sciences, University of Montana, Missoula, MT 59812, USA
| | - Giuseppe Gerna
- Laboratories of Genetics, Transplantology and Cardiovascular Diseases, Fondazione IRCCS Policlinico San Matteo, 27100 Pavia, Italy
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Wedemann L, Flomm FJ, Bosse JB. The unconventional way out-Egress of HCMV through multiviral bodies. Mol Microbiol 2022; 117:1317-1323. [PMID: 35607767 DOI: 10.1111/mmi.14946] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2022] [Revised: 05/18/2022] [Accepted: 05/21/2022] [Indexed: 12/14/2022]
Abstract
Human cytomegalovirus (HCMV) is a ubiquitous herpesvirus and the leading cause of congenital disabilities as well as a significant cause of disease in immunocompromised patients. The envelopment and egress of HCMV particles is an essential step of the viral life cycle as it determines viral spread and potentially tropism. Here we review the current literature on HCMV envelopment and egress with a particular focus on the role of virus-containing multivesicular body-like vesicles for virus egress and spread. We discuss the difficulties of determining the cellular provenance of these structures in light of viral redistribution of cellular marker proteins and provide potential paths to illuminate their genesis. Finally, we discuss how divergent egress pathways could result in virions of different tropisms.
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Affiliation(s)
- Linda Wedemann
- Centre for Structural Systems Biology, Hamburg, Germany.,Hannover Medical School, Institute of Virology, Hannover, Germany.,Cluster of Excellence RESIST (EXC 2155), Hannover Medical School, Hannover, Germany.,Leibniz-Institute of Virology, Hamburg, Germany
| | - Felix J Flomm
- Centre for Structural Systems Biology, Hamburg, Germany.,Hannover Medical School, Institute of Virology, Hannover, Germany.,Cluster of Excellence RESIST (EXC 2155), Hannover Medical School, Hannover, Germany.,Leibniz-Institute of Virology, Hamburg, Germany
| | - Jens B Bosse
- Centre for Structural Systems Biology, Hamburg, Germany.,Hannover Medical School, Institute of Virology, Hannover, Germany.,Cluster of Excellence RESIST (EXC 2155), Hannover Medical School, Hannover, Germany.,Leibniz-Institute of Virology, Hamburg, Germany
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Cryo-Electron Microscopy Structure and Interactions of the Human Cytomegalovirus gHgLgO Trimer with Platelet-Derived Growth Factor Receptor Alpha. mBio 2021; 12:e0262521. [PMID: 34700375 PMCID: PMC8546573 DOI: 10.1128/mbio.02625-21] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Human cytomegalovirus (HCMV) is a herpesvirus that produces disease in transplant patients and newborn children. Entry of HCMV into cells relies on gH/gL trimer (gHgLgO) and pentamer (gHgLUL128–131) complexes that bind cellular receptors. Here, we studied the structure and interactions of the HCMV trimer, formed by AD169 strain gH and gL and TR strain gO proteins, with the human platelet-derived growth factor receptor alpha (PDGFRα). Three trimer surfaces make extensive contacts with three PDGFRα N-terminal domains, causing PDGFRα to wrap around gO in a structure similar to a human hand, explaining the high-affinity interaction. gO is among the least conserved HCMV proteins, with 8 distinct genotypes. We observed high conservation of residues mediating gO-gL interactions but more extensive gO variability in the PDGFRα interface. Comparisons between our trimer structure and a previously determined structure composed of different subunit genotypes indicate that gO variability is accommodated by adjustments in the gO-PDGFRα interface. We identified two loops within gO that were disordered and apparently glycosylated, which could be deleted without disrupting PDGFRα binding. We also identified four gO residues that contact PDGFRα, which when mutated produced markedly reduced receptor binding. These residues fall within conserved contact sites of gO with PDGFRα and may represent key targets for anti-trimer neutralizing antibodies and HCMV vaccines. Finally, we observe that gO mutations distant from the gL interaction site impact trimer expression, suggesting that the intrinsic folding or stability of gO can impact the efficiency of trimer assembly.
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