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Membraneless Compartmentalization of Nuclear Assembly Sites during Murine Cytomegalovirus Infection. Viruses 2023; 15:v15030766. [PMID: 36992475 PMCID: PMC10053344 DOI: 10.3390/v15030766] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2022] [Revised: 02/28/2023] [Accepted: 03/14/2023] [Indexed: 03/19/2023] Open
Abstract
Extensive reorganization of infected cells and the formation of large structures known as the nuclear replication compartment (RC) and cytoplasmic assembly compartment (AC) is a hallmark of beta-herpesvirus infection. These restructurings rely on extensive compartmentalization of the processes that make up the virus manufacturing chain. Compartmentalization of the nuclear processes during murine cytomegalovirus (MCMV) infection is not well described. In this study, we visualized five viral proteins (pIE1, pE1, pM25, pm48.2, and pM57) and replicated viral DNA to reveal the nuclear events during MCMV infection. As expected, these events can be matched with those described for other beta and alpha herpesviruses and contribute to the overall picture of herpesvirus assembly. Imaging showed that four viral proteins (pE1, pM25, pm48.2, and pM57) and replicated viral DNA condense in the nucleus into membraneless assemblies (MLAs) that undergo a maturation sequence to form the RC. One of these proteins (pM25), which is also expressed in a cytoplasmic form (pM25l), showed similar MLAs in the AC. Bioinformatics tools for predicting biomolecular condensates showed that four of the five proteins had a high propensity for liquid–liquid phase separation (LLPS), suggesting that LLPS may be a mechanism for compartmentalization within RC and AC. Examination of the physical properties of MLAs formed during the early phase of infection by 1,6-hexanediol treatment in vivo revealed liquid-like properties of pE1 MLAs and more solid-like properties of pM25 MLAs, indicating heterogeneity of mechanisms in the formation of virus-induced MLAs. Analysis of the five viral proteins and replicated viral DNA shows that the maturation sequence of RC and AC is not completed in many cells, suggesting that virus production and release is carried out by a rather limited number of cells. This study thus lays the groundwork for further investigation of the replication cycle of beta-herpesviruses, and the results should be incorporated into plans for high-throughput and single-cell analytic approaches.
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Cruz-Cosme R, Zhang J, Liu D, Mahase V, Sallapalli BT, Chang P, Zhang Y, Teng S, Zhao RY, Tang Q. A novel diG motif in ORF3a protein of SARS-Cov-2 for intracellular transport. Front Cell Dev Biol 2022; 10:1011221. [PMID: 36506095 PMCID: PMC9727819 DOI: 10.3389/fcell.2022.1011221] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2022] [Accepted: 11/07/2022] [Indexed: 11/24/2022] Open
Abstract
The ongoing SARS-CoV-2/COVID-19 pandemic caused a global public health crisis. Yet, everyone's response to SARS-CoV-2 infection varies, and different viral variants confer diverse pathogenicity. Thus, it is imperative to understand how viral determinants contribute to COVID-19. Viral ORF3a protein is one of those viral determinants, as its functions are linked to induction of cell and tissues damages, disease severity and cytokine storm that is a major cause of COVID-19-related death. ORF3a is a membrane-associated protein. Upon synthesis, it is transported from endoplasmic reticulum, Golgi apparatus to plasma membrane and subcellular endomembranes including endosomes and lysosomes. However, how ORF3a is transported intracellularly remains elusive. The goal of this study was to carry out a systematic mutagenesis study to determine the structural relationship of ORF3a protein with its subcellular locations. Single amino acid (aa) and deletion mutations were generated in the putative function-relevant motifs and other regions of interest. Immunofluorescence and ImageJ analyses were used to determine and quantitate subcellular locations of ORF3a mutants in comparison with wildtype ORF3a. The wildtype ORF3a localizes predominantly (Pearson's coefficients about 0.8) on the membranes of endosomes and lysosomes. Consistent with earlier findings, deletion of the YXXΦ motif, which is required for protein export, retained ORF3a in the Golgi apparatus. Interestingly, mutations in a double glycine (diG) region (aa 187-188) displayed a similar phenotype to the YXXΦ deletion, implicating a similar role of the diG motif in intracellular transport. Indeed, interrupting any one of the two glycine residues such as deletion of a single (dG188), both (dG187/dG188) or substitution (G188Y) of these residues led to ORF3a retention in the Golgi apparatus (Pearson's coefficients ≥0.8). Structural analyses further suggest that the diG motif supports a type-II β-turn between the anti-parallel β4 and β5 sheets and connects to the YXXΦ motif via hydrogen bonds between two monomers. The diG- YXXΦ interaction forms a hand-in-hand configuration that could facilitate dimerization. Together, these observations suggest a functional role of the diG motif in intracellular transport of ORF3a.
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Affiliation(s)
- Ruth Cruz-Cosme
- Department of Microbiology, Howard University College of Medicine, Washington, DC, United States
| | - Jiantao Zhang
- Department of Pathology, University of Maryland School of Medicine, Baltimore, MD, United States
- Research and Development Service, VA Maryland Health Care System, Baltimore, MD, United States
| | - Dongxiao Liu
- Department of Microbiology, Howard University College of Medicine, Washington, DC, United States
| | - Vidhyanand Mahase
- Department of Biology, Howard University, Washington, DC, United States
| | | | - Peixi Chang
- Department of Veterinary Medicine, University of Maryland, College Park, MD, United States
| | - Yanjin Zhang
- Department of Veterinary Medicine, University of Maryland, College Park, MD, United States
| | - Shaolei Teng
- Department of Biology, Howard University, Washington, DC, United States
| | - Richard Y. Zhao
- Department of Pathology, University of Maryland School of Medicine, Baltimore, MD, United States
- Research and Development Service, VA Maryland Health Care System, Baltimore, MD, United States
- Department of Microbiology and Immunology, Institute of Human Virology, Institute of Global Health, University of Maryland School of Medicine, Baltimore, MD, United States
| | - Qiyi Tang
- Department of Microbiology, Howard University College of Medicine, Washington, DC, United States
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