The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Donald M Coen - One of the best experts on this subject based on the ideXlab platform.
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a role for myosin va in human cytomegalovirus nuclear egress
Journal of Virology, 2018Co-Authors: Adrian R Wilkie, Mayuri Sharma, Jean M Pesola, Maria Ericsson, Rosio Fernandez, Donald M CoenAbstract:Herpesviruses replicate and package their genomes into Capsids in replication compartments within the nuclear interior. Capsids then move to the inner nuclear membrane for envelopment and release into the cytoplasm in a process called nuclear egress. We previously found that nuclear F-actin is induced upon infection with the betaherpesvirus human cytomegalovirus (HCMV) and is important for nuclear egress and Capsid localization away from replication compartment-like inclusions toward the nuclear rim. Despite these and related findings, it has not been shown that any specific motor protein is involved in herpesvirus nuclear egress. In this study, we have investigated whether the host motor protein, myosin Va, could be fulfilling this role. Using immunofluorescence microscopy and coimmunoprecipitation, we observed associations between a nuclear population of myosin Va and the viral major Capsid protein, with both concentrating at the periphery of replication compartments. Immunoelectron microscopy showed that nearly 40% of assembled nuclear Capsids associate with myosin Va. We also found that myosin Va and major Capsid protein colocalize with nuclear F-actin. Importantly, antagonism of myosin Va with RNA interference or a dominant negative mutant revealed that myosin Va is important for the efficient production of infectious virus, Capsid accumulation in the cytoplasm, and Capsid localization away from replication compartment-like inclusions toward the nuclear rim. Our results lead us to suggest a working model whereby human cytomegalovirus Capsids associate with myosin Va for movement from replication compartments to the nuclear periphery during nuclear egress.IMPORTANCE Little is known regarding how newly assembled and packaged herpesvirus Capsids move from the nuclear interior to the periphery during nuclear egress. While it has been proposed that an actomyosin-based mechanism facilitates intranuclear movement of alphaherpesvirus Capsids, a functional role for any specific myosin in nuclear egress has not been reported. Furthermore, the notion that an actomyosin-based mechanism facilitates intranuclear Capsid movement is controversial. Here we show that human cytomegalovirus Capsids associate with nuclear myosin Va and F-actin and that antagonism of myosin Va impairs Capsid localization toward the nuclear rim and nuclear egress. Together with our previous results showing that nuclear F-actin is induced upon HCMV infection and is also important for these processes, our results lend support to the hypothesis that nascent human cytomegalovirus Capsids migrate to the nuclear periphery via actomyosin-based movement. These results shed light on a poorly understood viral process and the cellular machinery involved.
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getting to and through the inner nuclear membrane during herpesvirus nuclear egress
Current Opinion in Cell Biology, 2017Co-Authors: Ming F Lye, Adrian R Wilkie, David J Filman, James M Hogle, Donald M CoenAbstract:Herpesviruses, like most DNA viruses, replicate and package their genomes into Capsids in the host cell nucleus. Capsids then transit to the cytoplasm in a fascinating process called nuclear egress, which includes several unusual steps: Movement of Capsids from the nuclear interior to the periphery, disruption of the nuclear lamina, Capsid budding through the inner nuclear membrane, and fusion of enveloped particles with the outer nuclear membrane. Here, we review recent advances and emerging questions relating to herpesvirus nuclear egress, emphasizing controversies regarding mechanisms for Capsid trafficking to the nuclear periphery, and implications of recent structures of the two-subunit, viral nuclear egress complex for the process, particularly at the step of budding through the inner nuclear membrane.
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a role for nuclear f actin induction in human cytomegalovirus nuclear egress
Mbio, 2016Co-Authors: Adrian R Wilkie, Jessica L Lawler, Donald M CoenAbstract:ABSTRACT Herpesviruses, which include important pathogens, remodel the host cell nucleus to facilitate infection. This remodeling includes the formation of structures called replication compartments (RCs) in which herpesviruses replicate their DNA. During infection with the betaherpesvirus, human cytomegalovirus (HCMV), viral DNA synthesis occurs at the periphery of RCs within the nuclear interior, after which assembled Capsids must reach the inner nuclear membrane (INM) for translocation to the cytoplasm (nuclear egress). The processes that facilitate movement of HCMV Capsids to the INM during nuclear egress are unknown. Although an actin-based mechanism of alphaherpesvirus Capsid trafficking to the INM has been proposed, it is controversial. Here, using a fluorescently-tagged, nucleus-localized actin-binding peptide, we show that HCMV, but not herpes simplex virus 1, strongly induced nuclear actin filaments (F-actin) in human fibroblasts. Based on studies using UV inactivation and inhibitors, this induction depended on viral gene expression. Interestingly, by 24 h postinfection, nuclear F-actin formed thicker structures that appeared by super-resolution microscopy to be bundles of filaments. Later in infection, nuclear F-actin primarily localized along the RC periphery and between the RC periphery and the nuclear rim. Importantly, a drug that depolymerized nuclear F-actin caused defects in production of infectious virus, Capsid accumulation in the cytoplasm, and Capsid localization near the nuclear rim, without decreasing Capsid accumulation in the nucleus. Thus, our results suggest that for at least one herpesvirus, nuclear F-actin promotes Capsid movement to the nuclear periphery and nuclear egress. We discuss our results in terms of competing models for these processes. IMPORTANCE The mechanisms underlying herpesvirus nuclear egress have not been fully determined. In particular, how newly assembled Capsids move to the inner nuclear membrane for envelopment is uncertain and controversial. In this study, we show that HCMV, an important human pathogen, induces actin filaments in the nuclei of infected cells and that an inhibitor of nuclear F-actin impairs nuclear egress and Capsid localization toward the nuclear periphery. Herpesviruses are widespread pathogens that cause or contribute to an array of human diseases. A better understanding of how herpesvirus Capsids traffic in the nucleus may uncover novel targets for antiviral intervention and elucidate aspects of the nuclear cytoskeleton, about which little is known.
Adrian R Wilkie - One of the best experts on this subject based on the ideXlab platform.
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a role for myosin va in human cytomegalovirus nuclear egress
Journal of Virology, 2018Co-Authors: Adrian R Wilkie, Mayuri Sharma, Jean M Pesola, Maria Ericsson, Rosio Fernandez, Donald M CoenAbstract:Herpesviruses replicate and package their genomes into Capsids in replication compartments within the nuclear interior. Capsids then move to the inner nuclear membrane for envelopment and release into the cytoplasm in a process called nuclear egress. We previously found that nuclear F-actin is induced upon infection with the betaherpesvirus human cytomegalovirus (HCMV) and is important for nuclear egress and Capsid localization away from replication compartment-like inclusions toward the nuclear rim. Despite these and related findings, it has not been shown that any specific motor protein is involved in herpesvirus nuclear egress. In this study, we have investigated whether the host motor protein, myosin Va, could be fulfilling this role. Using immunofluorescence microscopy and coimmunoprecipitation, we observed associations between a nuclear population of myosin Va and the viral major Capsid protein, with both concentrating at the periphery of replication compartments. Immunoelectron microscopy showed that nearly 40% of assembled nuclear Capsids associate with myosin Va. We also found that myosin Va and major Capsid protein colocalize with nuclear F-actin. Importantly, antagonism of myosin Va with RNA interference or a dominant negative mutant revealed that myosin Va is important for the efficient production of infectious virus, Capsid accumulation in the cytoplasm, and Capsid localization away from replication compartment-like inclusions toward the nuclear rim. Our results lead us to suggest a working model whereby human cytomegalovirus Capsids associate with myosin Va for movement from replication compartments to the nuclear periphery during nuclear egress.IMPORTANCE Little is known regarding how newly assembled and packaged herpesvirus Capsids move from the nuclear interior to the periphery during nuclear egress. While it has been proposed that an actomyosin-based mechanism facilitates intranuclear movement of alphaherpesvirus Capsids, a functional role for any specific myosin in nuclear egress has not been reported. Furthermore, the notion that an actomyosin-based mechanism facilitates intranuclear Capsid movement is controversial. Here we show that human cytomegalovirus Capsids associate with nuclear myosin Va and F-actin and that antagonism of myosin Va impairs Capsid localization toward the nuclear rim and nuclear egress. Together with our previous results showing that nuclear F-actin is induced upon HCMV infection and is also important for these processes, our results lend support to the hypothesis that nascent human cytomegalovirus Capsids migrate to the nuclear periphery via actomyosin-based movement. These results shed light on a poorly understood viral process and the cellular machinery involved.
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getting to and through the inner nuclear membrane during herpesvirus nuclear egress
Current Opinion in Cell Biology, 2017Co-Authors: Ming F Lye, Adrian R Wilkie, David J Filman, James M Hogle, Donald M CoenAbstract:Herpesviruses, like most DNA viruses, replicate and package their genomes into Capsids in the host cell nucleus. Capsids then transit to the cytoplasm in a fascinating process called nuclear egress, which includes several unusual steps: Movement of Capsids from the nuclear interior to the periphery, disruption of the nuclear lamina, Capsid budding through the inner nuclear membrane, and fusion of enveloped particles with the outer nuclear membrane. Here, we review recent advances and emerging questions relating to herpesvirus nuclear egress, emphasizing controversies regarding mechanisms for Capsid trafficking to the nuclear periphery, and implications of recent structures of the two-subunit, viral nuclear egress complex for the process, particularly at the step of budding through the inner nuclear membrane.
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a role for nuclear f actin induction in human cytomegalovirus nuclear egress
Mbio, 2016Co-Authors: Adrian R Wilkie, Jessica L Lawler, Donald M CoenAbstract:ABSTRACT Herpesviruses, which include important pathogens, remodel the host cell nucleus to facilitate infection. This remodeling includes the formation of structures called replication compartments (RCs) in which herpesviruses replicate their DNA. During infection with the betaherpesvirus, human cytomegalovirus (HCMV), viral DNA synthesis occurs at the periphery of RCs within the nuclear interior, after which assembled Capsids must reach the inner nuclear membrane (INM) for translocation to the cytoplasm (nuclear egress). The processes that facilitate movement of HCMV Capsids to the INM during nuclear egress are unknown. Although an actin-based mechanism of alphaherpesvirus Capsid trafficking to the INM has been proposed, it is controversial. Here, using a fluorescently-tagged, nucleus-localized actin-binding peptide, we show that HCMV, but not herpes simplex virus 1, strongly induced nuclear actin filaments (F-actin) in human fibroblasts. Based on studies using UV inactivation and inhibitors, this induction depended on viral gene expression. Interestingly, by 24 h postinfection, nuclear F-actin formed thicker structures that appeared by super-resolution microscopy to be bundles of filaments. Later in infection, nuclear F-actin primarily localized along the RC periphery and between the RC periphery and the nuclear rim. Importantly, a drug that depolymerized nuclear F-actin caused defects in production of infectious virus, Capsid accumulation in the cytoplasm, and Capsid localization near the nuclear rim, without decreasing Capsid accumulation in the nucleus. Thus, our results suggest that for at least one herpesvirus, nuclear F-actin promotes Capsid movement to the nuclear periphery and nuclear egress. We discuss our results in terms of competing models for these processes. IMPORTANCE The mechanisms underlying herpesvirus nuclear egress have not been fully determined. In particular, how newly assembled Capsids move to the inner nuclear membrane for envelopment is uncertain and controversial. In this study, we show that HCMV, an important human pathogen, induces actin filaments in the nuclei of infected cells and that an inhibitor of nuclear F-actin impairs nuclear egress and Capsid localization toward the nuclear periphery. Herpesviruses are widespread pathogens that cause or contribute to an array of human diseases. A better understanding of how herpesvirus Capsids traffic in the nucleus may uncover novel targets for antiviral intervention and elucidate aspects of the nuclear cytoskeleton, about which little is known.
Adam Zlotnick - One of the best experts on this subject based on the ideXlab platform.
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hepatitis b virus Capsid completion occurs through error correction
Journal of the American Chemical Society, 2017Co-Authors: Corinne A Lutomski, Adam Zlotnick, Elizabeth E Pierson, Nicholas A Lyktey, Zhongchao Zhao, Martin F JarroldAbstract:Understanding Capsid assembly is important because of its role in virus lifecycles and in applications to drug discovery and nanomaterial development. Many virus Capsids are icosahedral, and assembly is thought to occur by the sequential addition of Capsid protein subunits to a nucleus, with the final step completing the icosahedron. Almost nothing is known about the final (completion) step because the techniques usually used to study Capsid assembly lack the resolution. In this work, charge detection mass spectrometry (CDMS) has been used to track the assembly of the T = 4 hepatitis B virus (HBV) Capsid in real time. The initial assembly reaction occurs rapidly, on the time scale expected from low resolution measurements. However, CDMS shows that many of the particles generated in this process are defective and overgrown, containing more than the 120 Capsid protein dimers needed to form a perfect T = 4 icosahedron. The defective and overgrown Capsids self-correct over time to the mass expected for a perfect T = 4 Capsid. Thus, completion is a distinct phase in the assembly reaction. Capsid completion does not necessarily occur by inserting the last building block into an incomplete, but otherwise perfect icosahedron. The initial assembly reaction can be predominently imperfect, and completion involves the slow correction of the accumulated errors.
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a molecular breadboard removal and replacement of subunits in a hepatitis b virus Capsid
Protein Science, 2017Co-Authors: Lye Siang Lee, Nicholas E Brunk, Daniel G Haywood, David Z Keifer, Elizabeth E Pierson, Panagiotis Kondylis, Joseph Cheyen Wang, Stephen C Jacobson, Martin F Jarrold, Adam ZlotnickAbstract:Hepatitis B virus (HBV) core protein is a model system for studying assembly and disassembly of icosahedral structures. Controlling disassembly will allow re-engineering the 120 subunit HBV Capsid, making it a molecular breadboard. We examined removal of subunits from partially crosslinked Capsids to form stable incomplete particles. To characterize incomplete Capsids, we used two single molecule techniques, resistive-pulse sensing and charge detection mass spectrometry. We expected to find a binomial distribution of Capsid fragments. Instead, we found a preponderance of 3 MDa complexes (90 subunits) and no fragments smaller than 3 MDa. We also found 90-mers in the disassembly of uncrosslinked HBV Capsids. 90-mers seem to be a common pause point in disassembly reactions. Partly explaining this result, graph theory simulations have showed a threshold for Capsid stability between 80 and 90 subunits. To test a molecular breadboard concept, we showed that missing subunits could be refilled resulting in chimeric, 120 subunit particles. This result may be a means of assembling unique Capsids with functional decorations. This article is protected by copyright. All rights reserved.
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the hepatitis b virus core protein intradimer interface modulates Capsid assembly and stability
Biochemistry, 2014Co-Authors: Lisa Selzer, Sarah P Katen, Adam ZlotnickAbstract:During the hepatitis B virus (HBV) life cycle, Capsid assembly and disassembly must ensure correct packaging and release of the viral genome. Here we show that changes in the dynamics of the core protein play an important role in regulating these processes. The HBV Capsid assembles from 120 copies of the core protein homodimer. Each monomer contains a conserved cysteine at position 61 that can form an intradimer disulfide that we use as a marker for dimer conformational states. We show that dimers in the context of Capsids form intradimer disulfides relatively rapidly. Surprisingly, compared to reduced dimers, fully oxidized dimers assembled slower and into Capsids that were morphologically similar but less stable. We hypothesize that oxidized protein adopts a geometry (or constellation of geometries) that is unfavorable for Capsid assembly, resulting in weaker dimer-dimer interactions as well as slower assembly kinetics. Our results suggest that structural flexibility at the core protein intradimer interface is essential for regulating Capsid assembly and stability. We further suggest that Capsid destabilization by the C61-C61 disulfide has a regulatory function to support Capsid disassembly and release of the viral genome.
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weak protein protein interactions are sufficient to drive assembly of hepatitis b virus Capsids
Biochemistry, 2002Co-Authors: Pablo Ceres, Adam ZlotnickAbstract:Hepatitis B virus (HBV) is an enveloped DNA virus with a spherical Capsid (or core). The Capsid is constructed from 120 copies of the homodimeric Capsid protein arranged with T = 4 icosahedral symmetry. We examined in vitro assembly of purified E. coli expressed HBV Capsid protein. After equilibration, concentrations of Capsid and dimer were evaluated by size exclusion chromatography. The extent of assembly increased as temperature and ionic strength increased. The concentration dependence of Capsid assembly conformed to the equilibrium expression: KCapsid = [Capsid]/[dimer]120. Given the known geometry for HBV Capsids and dimers, the per Capsid assembly energy was partitioned into energy per subunit−subunit contact. We were able to make three major conclusions. (i) Weak interactions (from −2.9 kcal/mol at 21 °C in low salt to −4.4 kcal/mol at 37 °C in high salt) at each intersubunit contact result in a globally stable Capsid; weak intersubunit interactions may be the basis for the phenomenon of Capsid b...
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dimorphism of hepatitis b virus Capsids is strongly influenced by the c terminus of the Capsid protein
Biochemistry, 1996Co-Authors: Adam Zlotnick, Naiqian Cheng, James F Conway, Frank P Booy, A C Steven, Stephen J Stahl, Paul T WingfieldAbstract:Hepatitis B virus (HBV) is an enveloped virus with an icosahedral Capsid. Its homodimeric Capsid protein (“core antigen”) assembles into particles of two sizes, one with T = 3 icosahedral symmetry (90 dimers) and the other with T = 4 symmetry (120 dimers). We have investigated this assembly process in vitro, using a variety of purified, bacterially expressed, Capsid proteins. All of our constructs lacked the predominantly basic C-terminal 34 amino acids of the full-length Capsid protein (183 amino acids) and were further truncated to terminate at specific points between residues 138 and 149. While the smallest construct (138 residues) did not assemble into Capsids, those terminating at residue 140, and beyond, assembled into mixtures of T = 3 and T = 4 particles. The two kinds of Capsids could be separated on sucrose gradients and did not interconvert upon protracted storage. The proportion of T = 3 Capsids, assayed by sucrose gradient fractionation, analytical ultracentrifugation, and cryoelectron micros...
Michael Kann - One of the best experts on this subject based on the ideXlab platform.
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nucleoporin 153 arrests the nuclear import of hepatitis b virus Capsids in the nuclear basket
PLOS Pathogens, 2010Co-Authors: Andre Schmitz, Birgit Rabe, Nelly Pante, Michael Kann, Alexandra Schwarz, Michael Foss, Lixin Zhou, Julia Hoellenriegel, Miriam Carolin StoeberAbstract:Virtually all DNA viruses including hepatitis B viruses (HBV) replicate their genome inside the nucleus. In non-dividing cells, the genome has to pass through the nuclear pore complexes (NPCs) by the aid of nuclear transport receptors as e.g. importin β (karyopherin). Most viruses release their genome in the cytoplasm or at the cytosolic face of the NPC, as the diameter of their Capsids exceeds the size of the NPC. The DNA genome of HBV is derived from reverse transcription of an RNA pregenome. Genome maturation occurs in cytosolic Capsids and progeny Capsids can deliver the genome into the nucleus causing nuclear genome amplification. The karyophilic Capsids are small enough to pass the NPC, but nuclear entry of Capsids with an immature genome is halted in the nuclear basket on the nuclear side of the NPC, and the genome remains enCapsidated. In contrast, Capsids with a mature genome enter the basket and consequently liberate the genome. Investigating the difference between immature and mature Capsids, we found that mature Capsids had to disintegrate in order to leave the nuclear basket. The arrest of a karyophilic cargo at the nuclear pore is a rare phenomenon, which has been described for only very few cellular proteins participating in nuclear entry. We analyzed the interactions causing HBV Capsid retention. By pull-down assays and partial siRNA depletion, we showed that HBV Capsids directly interact with nucleoporin 153 (Nup153), an essential protein of the nuclear basket which participates in nuclear transport via importin β. The binding sites of importin β and Capsids were shown to overlap but Capsid binding was 150-fold stronger. In cellulo experiments using digitonin-permeabilized cells confirmed the interference between Capsid binding and nuclear import by importin β. Collectively, our findings describe a unique nuclear import strategy not only for viruses but for all karyophilic cargos.
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nuclear import of hepatitis b virus Capsids and release of the viral genome
Proceedings of the National Academy of Sciences of the United States of America, 2003Co-Authors: Birgit Rabe, Angelika Vlachou, Nelly Pante, Ari Helenius, Michael KannAbstract:While studying the import of the hepatitis B virus genome into the nucleus of permeabilized tissue culture cells, we found that viral Capsids were imported in intact form through the nuclear pore into the nuclear basket. Import depended on phosphorylation of the Capsid protein and was mediated by the cellular transport receptors importin α and β. Virus-derived Capsids that contained the mature viral genome were able to release the viral DNA and Capsid protein into the nucleoplasm. The uncoating reaction was independent of Ran, a GTP-binding enzyme responsible for dissociating other imported cargoes from the inner face of the nuclear pore. Immature Capsids that did not contain the mature viral genome reached the basket but did not release Capsid proteins nor immature genomes into the nucleoplasm. The different fate of mature and immature Capsids after passing the nuclear pore indicates that the outcome of a nuclear import event may be regulated within the nuclear basket.
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central role of a serine phosphorylation site within duck hepatitis b virus core protein for Capsid trafficking and genome release
Journal of Biological Chemistry, 2003Co-Authors: Josef Kock, Michael Kann, Gerhard Putz, H E Blum, Fritz Von WeizsackerAbstract:Viral nucleoCapsids compartmentalize and protect viral genomes during assembly while they mediate targeted genome release during viral infection. This dual role of the Capsid in the viral life cycle must be tightly regulated to ensure efficient virus spread. Here, we used the duck hepatitis B virus (DHBV) infection model to analyze the effects of Capsid phosphorylation and hydrogen bond formation. The potential key phosphorylation site at serine 245 within the core protein, the building block of DHBV Capsids, was substituted by alanine (S245A), aspartic acid (S245D) and asparagine (S245N), respectively. Mutant Capsids were analyzed for replication competence, stability, nuclear transport, and infectivity. All mutants formed DHBV DNA-containing nucleoCapsids. Wild-type and S245N but not S245A and S245D fully protected Capsid-associated mature viral DNA from nuclease action. A negative ionic charge as contributed by phosphorylated serine or aspartic acid-supported nuclear localization of the viral Capsid and generation of nuclear superhelical DNA. Finally, wild-type and S245D but not S245N virions were infectious in primary duck hepatocytes. These results suggest that hydrogen bonds formed by non-phosphorylated serine 245 stabilize the quarterny structure of DHBV nucleoCapsids during viral assembly, while serine phosphorylation plays an important role in nuclear targeting and DNA release from Capsids during viral infection.
John A G Briggs - One of the best experts on this subject based on the ideXlab platform.
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structure of the ty3 gypsy retrotransposon Capsid and the evolution of retroviruses
Proceedings of the National Academy of Sciences of the United States of America, 2019Co-Authors: S O Dodonova, Simone Prinz, Virginia Bilanchone, Suzanne Sandmeyer, John A G BriggsAbstract:Retroviruses evolved from long terminal repeat (LTR) retrotransposons by acquisition of envelope functions, and subsequently reinvaded host genomes. Together, endogenous retroviruses and LTR retrotransposons represent major components of animal, plant, and fungal genomes. Sequences from these elements have been exapted to perform essential host functions, including placental development, synaptic communication, and transcriptional regulation. They encode a Gag polypeptide, the Capsid domains of which can oligomerize to form a virus-like particle. The structures of retroviral Capsids have been extensively described. They assemble an immature viral particle through oligomerization of full-length Gag. Proteolytic cleavage of Gag results in a mature, infectious particle. In contrast, the absence of structural data on LTR retrotransposon Capsids hinders our understanding of their function and evolutionary relationships. Here, we report the Capsid morphology and structure of the archetypal Gypsy retrotransposon Ty3. We performed electron tomography (ET) of immature and mature Ty3 particles within cells. We found that, in contrast to retroviruses, these do not change size or shape upon maturation. Cryo-ET and cryo-electron microscopy of purified, immature Ty3 particles revealed an irregular fullerene geometry previously described for mature retrovirus core particles and a tertiary and quaternary arrangement of the Capsid (CA) C-terminal domain within the assembled Capsid that is conserved with mature HIV-1. These findings provide a structural basis for studying retrotransposon Capsids, including those domesticated in higher organisms. They suggest that assembly via a structurally distinct immature Capsid is a later retroviral adaptation, while the structure of mature assembled Capsids is conserved between LTR retrotransposons and retroviruses.
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structure of the ty3 gypsy retrotransposon Capsid and the evolution of retroviruses
Proceedings of the National Academy of Sciences of the United States of America, 2019Co-Authors: S O Dodonova, Simone Prinz, Virginia Bilanchone, Suzanne Sandmeyer, John A G BriggsAbstract:Retroviruses evolved from long terminal repeat (LTR) retrotransposons by acquisition of envelope functions, and subsequently reinvaded host genomes. Together, endogenous retroviruses and LTR retrotransposons represent major components of animal, plant, and fungal genomes. Sequences from these elements have been exapted to perform essential host functions, including placental development, synaptic communication, and transcriptional regulation. They encode a Gag polypeptide, the Capsid domains of which can oligomerize to form a virus-like particle. The structures of retroviral Capsids have been extensively described. They assemble an immature viral particle through oligomerization of full-length Gag. Proteolytic cleavage of Gag results in a mature, infectious particle. In contrast, the absence of structural data on LTR retrotransposon Capsids hinders our understanding of their function and evolutionary relationships. Here, we report the Capsid morphology and structure of the archetypal Gypsy retrotransposon Ty3. We performed electron tomography (ET) of immature and mature Ty3 particles within cells. We found that, in contrast to retroviruses, these do not change size or shape upon maturation. Cryo-ET and cryo-electron microscopy of purified, immature Ty3 particles revealed an irregular fullerene geometry previously described for mature retrovirus core particles and a tertiary and quaternary arrangement of the Capsid (CA) C-terminal domain within the assembled Capsid that is conserved with mature HIV-1. These findings provide a structural basis for studying retrotransposon Capsids, including those domesticated in higher organisms. They suggest that assembly via a structurally distinct immature Capsid is a later retroviral adaptation, while the structure of mature assembled Capsids is conserved between LTR retrotransposons and retroviruses.