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Viruses Feb 2022The assembly of HIV-1 particles is a concerted and dynamic process that takes place on the plasma membrane of infected cells. An abundance of recent discoveries has... (Review)
Review
The assembly of HIV-1 particles is a concerted and dynamic process that takes place on the plasma membrane of infected cells. An abundance of recent discoveries has advanced our understanding of the complex sequence of events leading to HIV-1 particle assembly, budding, and release. Structural studies have illuminated key features of assembly and maturation, including the dramatic structural transition that occurs between the immature Gag lattice and the formation of the mature viral capsid core. The critical role of inositol hexakisphosphate (IP6) in the assembly of both the immature and mature Gag lattice has been elucidated. The structural basis for selective packaging of genomic RNA into virions has been revealed. This review will provide an overview of the HIV-1 assembly process, with a focus on recent advances in the field, and will point out areas where questions remain that can benefit from future investigation.
Topics: HIV-1; Virion; Virus Assembly; gag Gene Products, Human Immunodeficiency Virus
PubMed: 35336885
DOI: 10.3390/v14030478 -
Cell Jan 2018The neuronal gene Arc is essential for long-lasting information storage in the mammalian brain, mediates various forms of synaptic plasticity, and has been implicated in...
The neuronal gene Arc is essential for long-lasting information storage in the mammalian brain, mediates various forms of synaptic plasticity, and has been implicated in neurodevelopmental disorders. However, little is known about Arc's molecular function and evolutionary origins. Here, we show that Arc self-assembles into virus-like capsids that encapsulate RNA. Endogenous Arc protein is released from neurons in extracellular vesicles that mediate the transfer of Arc mRNA into new target cells, where it can undergo activity-dependent translation. Purified Arc capsids are endocytosed and are able to transfer Arc mRNA into the cytoplasm of neurons. These results show that Arc exhibits similar molecular properties to retroviral Gag proteins. Evolutionary analysis indicates that Arc is derived from a vertebrate lineage of Ty3/gypsy retrotransposons, which are also ancestors to retroviruses. These findings suggest that Gag retroelements have been repurposed during evolution to mediate intercellular communication in the nervous system.
Topics: Animals; Cells, Cultured; Cytoskeletal Proteins; Endocytosis; Exosomes; Female; Gene Products, gag; HEK293 Cells; Humans; Male; Mice; Mice, Inbred C57BL; Nerve Tissue Proteins; Neurons; RNA, Messenger
PubMed: 29328916
DOI: 10.1016/j.cell.2017.12.024 -
International Journal of Molecular... Jul 2022Once merely thought of as the protein responsible for the overall physical nature of the human immunodeficiency virus type 1 (HIV-1), the Gag polyprotein has since been... (Review)
Review
Once merely thought of as the protein responsible for the overall physical nature of the human immunodeficiency virus type 1 (HIV-1), the Gag polyprotein has since been elucidated to have several roles in viral replication and functionality. Over the years, extensive research into the polyproteins' structure has revealed that Gag can mediate its own trafficking to the plasma membrane, it can interact with several host factors and can even aid in viral genome packaging. Not surprisingly, Gag has also been associated with HIV-1 drug resistance and even treatment failure. Therefore, this review provides an extensive overview of the structural and functional roles of the HIV-1 Gag domains in virion integrity, functionality and infectivity.
Topics: HIV-1; Humans; Virion; Virus Replication; gag Gene Products, Human Immunodeficiency Virus
PubMed: 35886917
DOI: 10.3390/ijms23147569 -
Seminars in Cell & Developmental Biology Feb 2019Retroviral Gag proteins are responsible for coordinating many aspects of virion assembly. Gag possesses two distinct nucleic acid binding domains, matrix (MA) and... (Review)
Review
Retroviral Gag proteins are responsible for coordinating many aspects of virion assembly. Gag possesses two distinct nucleic acid binding domains, matrix (MA) and nucleocapsid (NC). One of the critical functions of Gag is to specifically recognize, bind, and package the retroviral genomic RNA (gRNA) into assembling virions. Gag interactions with cellular RNAs have also been shown to regulate aspects of assembly. Recent results have shed light on the role of MA and NC domain interactions with nucleic acids, and how they jointly function to ensure packaging of the retroviral gRNA. Here, we will review the literature regarding RNA interactions with NC, MA, as well as overall mechanisms employed by Gag to interact with RNA. The discussion focuses on human immunodeficiency virus type-1, but other retroviruses will also be discussed. A model is presented combining all of the available data summarizing the various factors and layers of selection Gag employs to ensure specific gRNA packaging and correct virion assembly.
Topics: Gene Products, gag; Genome, Viral; RNA, Viral; Retroviridae; Virus Assembly
PubMed: 29580971
DOI: 10.1016/j.semcdb.2018.03.015 -
Viruses Jul 2017Drosophila and extant species are the best-studied telomerase exception. In this organism, telomere elongation is coupled with targeted retrotransposition of Healing... (Review)
Review
Drosophila and extant species are the best-studied telomerase exception. In this organism, telomere elongation is coupled with targeted retrotransposition of Healing Transposon (HeT-A) and Telomere Associated Retrotransposon (TART) with sporadic additions of Telomere Associated and HeT-A Related (TAHRE), all three specialized non-Long Terminal Repeat (non-LTR) retrotransposons. These three very special retroelements transpose in head to tail arrays, always in the same orientation at the end of the chromosomes but never in interior locations. Apparently, retrotransposon and telomerase telomeres might seem very different, but a detailed view of their mechanisms reveals similarities explaining how the loss of telomerase in a Drosophila ancestor could successfully have been replaced by the telomere retrotransposons. In this review, we will discover that although HeT-A, TART, and TAHRE are still the only examples to date where their targeted transposition is perfectly tamed into the telomere biology of Drosophila, there are other examples of retrotransposons that manage to successfully integrate inside and at the end of telomeres. Because the aim of this special issue is viral integration at telomeres, understanding the base of the telomerase exceptions will help to obtain clues on similar strategies that mobile elements and viruses could have acquired in order to ensure their survival in the host genome.
Topics: Animals; Drosophila; Drosophila Proteins; Gene Products, gag; Retroelements; Telomere
PubMed: 28753967
DOI: 10.3390/v9070192 -
Viruses Mar 2013Gag proteins play an important role in many stages of the retroviral replication cycle. They orchestrate viral assembly, interact with numerous host cell proteins,... (Review)
Review
Gag proteins play an important role in many stages of the retroviral replication cycle. They orchestrate viral assembly, interact with numerous host cell proteins, engage in regulation of viral gene expression, and provide the main driving force for virus intracellular trafficking and budding. Foamy Viruses (FV), also known as spumaviruses, display a number of unique features among retroviruses. Many of these features can be attributed to their Gag proteins. FV Gag proteins lack characteristic orthoretroviral domains like membrane-binding domains (M domains), the major homology region (MHR), and the hallmark Cys-His motifs. In contrast, they contain several distinct domains such as the essential Gag-Env interaction domain and the glycine and arginine rich boxes (GR boxes). Furthermore, FV Gag only undergoes limited maturation and follows an unusual pathway for nuclear translocation. This review summarizes the known FV Gag domains and motifs and their functions. In particular, it provides an overview of the unique structural and functional properties that distinguish FV Gag proteins from orthoretroviral Gag proteins.
Topics: Animals; Gene Products, gag; Host-Pathogen Interactions; Humans; Protein Binding; Protein Interaction Domains and Motifs; Spumavirus; Virus Replication
PubMed: 23531622
DOI: 10.3390/v5041023 -
Journal of Molecular Biology Apr 2014The early events in the retrovirus assembly pathway, particularly the timing and nature of Gag translocation from the site of protein translation to the inner leaflet of...
The early events in the retrovirus assembly pathway, particularly the timing and nature of Gag translocation from the site of protein translation to the inner leaflet of the plasma membrane, are poorly understood. We have investigated the interrelationship between cytoplasmic Gag concentration and plasma membrane association using complementary live-cell biophysical fluorescence techniques in real time with both human T-cell leukemia virus type 1 (HTLV-1) and human immunodeficiency virus type 1 (HIV-1) Gag proteins. In particular, dual-color, z-scan fluorescence fluctuation spectroscopy in conjunction with total internal reflection fluorescence and conventional, epi-illumination imaging were utilized. Our results demonstrate that HTLV-1 Gag is capable of membrane targeting and particle assembly at low (i.e., nanomolar) cytoplasmic concentrations and that there is a critical threshold concentration (approaching micromolar) prior to the observation of HIV-1 Gag associated with the plasma membrane. These observations imply fundamental differences between HIV-1 and HTLV-1 Gag trafficking and membrane association.
Topics: Cell Membrane; Cytoplasm; Gene Products, gag; Human T-lymphotropic virus 1; Retroviridae; gag Gene Products, Human Immunodeficiency Virus
PubMed: 24316368
DOI: 10.1016/j.jmb.2013.11.025 -
The Journal of Cell Biology Aug 2003To efficiently bud off from infected cells, HIV and other enveloped viruses hijack the host cellular machinery that is normally involved in vacuolar protein sorting and... (Review)
Review
To efficiently bud off from infected cells, HIV and other enveloped viruses hijack the host cellular machinery that is normally involved in vacuolar protein sorting and multivesicular body (MVB) biogenesis. The HIV Gag protein mimics hepatocyte growth factor-regulated tyrosine kinase substrate (Hrs), a modular adaptor protein that links membrane cargo recognition to its degradation after delivery to MVBs. In contrast to T cells, where HIV budding occurs at the plasma membrane, virus buds into vacuoles of macrophages, a process that may facilitate its spread within the infected host.
Topics: Endosomal Sorting Complexes Required for Transport; Endosomes; Gene Products, gag; HIV; Humans; Macrophages; Molecular Mimicry; Phosphoproteins; Protein Transport; Virus Replication; Virus Shedding; gag Gene Products, Human Immunodeficiency Virus
PubMed: 12900390
DOI: 10.1083/jcb.200307062 -
The Journal of Biological Chemistry Jan 2022In HIV, the polyprotein precursor Gag orchestrates the formation of the viral capsid. In the current view of this viral assembly, Gag forms low-order oligomers that bind...
In HIV, the polyprotein precursor Gag orchestrates the formation of the viral capsid. In the current view of this viral assembly, Gag forms low-order oligomers that bind to the viral genomic RNA triggering the formation of high-ordered ribonucleoprotein complexes. However, this assembly model was established using biochemical or imaging methods that do not describe the cellular location hosting Gag-gRNA complex nor distinguish gRNA packaging in single particles. Here, we studied the intracellular localization of these complexes by electron microscopy and monitored the distances between the two partners by morphometric analysis of gold beads specifically labeling Gag and gRNA. We found that formation of these viral clusters occurred shortly after the nuclear export of the gRNA. During their transport to the plasma membrane, the distance between Gag and gRNA decreases together with an increase of gRNA packaging. Point mutations in the zinc finger patterns of the nucleocapsid domain of Gag caused an increase in the distance between Gag and gRNA as well as a sharp decrease of gRNA packaged into virions. Finally, we show that removal of stem loop 1 of the 5'-untranslated region does not interfere with gRNA packaging, whereas combined with the removal of stem loop 3 is sufficient to decrease but not abolish Gag-gRNA cluster formation and gRNA packaging. In conclusion, this morphometric analysis of Gag-gRNA cluster formation sheds new light on HIV-1 assembly that can be used to describe at nanoscale resolution other viral assembly steps involving RNA or protein-protein interactions.
Topics: 5' Untranslated Regions; Gene Products, gag; Genomics; HIV-1; Microscopy, Electron, Transmission; Nucleoproteins; RNA, Viral; Virus Assembly
PubMed: 34929171
DOI: 10.1016/j.jbc.2021.101500 -
Viruses Jul 2019The feline immunodeficiency virus (FIV) full-length Pr50 precursor is a key player in the assembly of new viral particles. It is also a critical component of the...
The feline immunodeficiency virus (FIV) full-length Pr50 precursor is a key player in the assembly of new viral particles. It is also a critical component of the efficient selection and packaging of two copies of genomic RNA (gRNA) into the newly formed virus particles from a wide pool of cellular and spliced viral RNA. To understand the molecular mechanisms involved during FIV gRNA packaging, we expressed the His-tagged and untagged recombinant FIV Pr50 protein both in eukaryotic and prokaryotic cells. The recombinant Pr50-His-tag fusion protein was purified from soluble fractions of prokaryotic cultures using immobilized metal affinity chromatography (IMAC). This purified protein was able to assemble in vitro into virus-like particles (VLPs), indicating that it preserved its ability to oligomerize/multimerize. Furthermore, VLPs formed in eukaryotic cells by the FIV full-length Pr50 both in the presence and absence of His-tag could package FIV sub-genomic RNA to similar levels, suggesting that the biological activity of the recombinant full-length Pr50 fusion protein was retained in the presence of His-tag at the carboxy terminus. Successful expression and purification of a biologically active, recombinant full-length Pr50-His-tag fusion protein will allow study of the intricate RNA-protein interactions involved during FIV gRNA encapsidation.
Topics: Animals; Cats; Escherichia coli; Gene Expression; Gene Products, gag; Genome, Viral; HEK293 Cells; Humans; Immunodeficiency Virus, Feline; RNA, Viral; Recombinant Proteins; Virus Assembly
PubMed: 31357656
DOI: 10.3390/v11080689