The Art of Reconstruction. In order to survive, viruses must be able to do the following:. 1. Find a host cell it can replicate in. 2. Bind to that cell. 3. Enter the cell. 4. Release its genome in order to replicate.
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Virus Life Cycles in 3D
Presentation on theme: "Virus Life Cycles in 3D"— Presentation transcript:
Virus Life Cycles in 3D
The Art of ReconstructionSlide2
In order to survive, viruses must be able to do the following:
1. Find a host cell it can replicate in
2. Bind to that cell3. Enter the cell4. Release its genome in order to replicate5. Replicate its genome6. Transcribe and translate its viral proteins7. Package its genome and proteins8. Escape from the cell
Virus Life CycleSlide3
Virus Life CycleSlide4
All these processes can be visualized by
These visualizations allows for a better understanding of viruses and may lead to vaccination developmentFor each virus, there is a unique life cycle but all viruses accomplish the same steps in order to survive Virus Life CycleSlide5
Semliki Forest Virus is an enveloped
It has 2 transmembrane proteins (E1 and E2) in its envelopeThe virus binds to the cellular receptor, endocytosed, and fuses with the endosome membrane to release its nucleocapsid for replication
SFV as an exampleSlide7
Poliovirus is a non enveloped virus in the
familyIt differs from SFV in that when it binds to its cellular receptor, it goes through a conformational change.This conformational change may facilitate the release of genome into the cell for replicationAlso releases from the cell by lysis instead of budding
Non enveloped VirusesSlide8
Non enveloped virusSlide9
The first step in viral replication is to be able to bind to the correct host cell.
Virus recognize host cells by certain receptors.
Bind to these receptors through specific interactions.Binding sites on viruses are typically conserved to ensure survivalCell AttachmentSlide10
Picornaviruses shield their receptor binding site in a region called the canyon in order to protect it from antibodies.
Must be conserved so that the virus can bind to the correct cell in order to replicate.
HRV16 + ICAM-1 interaction was one of the first to be studied through cryoWas believed that the binding site for ICAM-1 was located in the canyon region of HRV16
The Receptor binding region
The Receptor binding region
with the 2 N terminal domains of ICAM-1
The footprint of ICAM-1 was centered over the canyon as predicted showing that the canyon was in fact the binding site of the receptorHRV16 complexed with ICAM-1Slide13
VP4 of rotavirus is important to the viral life cycle
It is a determinant of virulence, has
hemagglutination activity and is also a neutralization siteThe reconstruction showed that VP4 extends from the surface of the virus, which may then be able to bind to the cellular receptor more easilySimian RotavirusSlide15
Simian Rotavirus Slide16
Viruses must be stable enough to survive the extracellular environment but must also be unstable enough to release their genome when they reach susceptible cells.
Certain conformational changes must occur in the virus when it reaches the proper environment in order to release its genome in the correct place and at the correct time.
SFV has a spike protruding from its envelope comprised of E1, E2, and E3
Reconstruction showed that the spike has a hole in its center
From previous studies, E3 was determined to be on the outside of the spikePreferential extraction and reconstruction comparison determined that E1made up the outside of the spike while E2 extended from the centerSFV SpikesSlide18
SFV with envelope and capsidSlide19
SFV spike structureSlide20
SFV spike structureSlide21
In order to determine the conformational changes needed for activation, the particles were treated with low pH and vitrified within milliseconds
Comparison between treated and untreated particle reconstructions showed that E1 and E2 move around each other
E2 is the receptor binding portion while E1 is the membrane fusion proteinE2 moves outward while E1 moves inward to form a trimmer and trigger fusionSFV spike conformational changesSlide22
SFV spike conformational changesSlide23
SFV process of fusionSlide24
Adenovirus is made up of hexons
and two proteins at the five fold
vertice: penton base and fiberIt binds two receptors: CAR and an integrinCAR binds to the fiber while the penton base binds the integrin and causes activationAdenovirusSlide25
Adenovirus 2 and hexonsSlide26
Adenovirus uses 2 receptors
The conformational changes needed for activation were determined by comparing particles which had the fiber attached and which did not
A small region which was determined to contain the RGD sequence by
MAb binding changed orientationStructural changes in pentonSlide28
Structural changes in pentonSlide29
The genome of the virus is released in order to make viral proteins and reproduce the genome.
Viruses can employ several strategies to do this: injection, release into the cytoplasm, release into the nucleus
Exception: ReovirusesGenome ReleaseSlide30
FHV is comprised of 180 copies of a single protein which undergoes a post assembly cleavage
The cleavage produces
γ peptides which lie in different orientations according to the subunit it is located onγa lies in pentamers under the five foldγb interacts with the bulk RNA and γc
with the ordered RNA
Flock House VirusSlide31
Flock House VirusSlide32
This data suggested a method of FHV entry and release of genome
The virus binds and contacts the membrane at the five fold vertex
The contact releases a pocket factor which then allows the γa pentamer to insert into the membraneThe RNA is then dragged into the cell by its contacts by the other γ peptide contacts
FHV entry into cellSlide34
FHV entry into cellSlide35
CCMV releases its genome by expansion
At low metal ion concentration and high pH, the particle swells
The particle does not fall apart due to interactions between subunits and RNAHowever, the three fold vertices open up which allow for flow of moleculesCCMV particle expansionSlide36
CCMV particle expansionSlide37
In order to multiply, the virus must be able to produce viral proteins and replicate its genome.
Process is intrinsically asymmetric which leads to difficulties in icosahedral reconstructions.
Reovirus have provided many clues to the process due to its unusual replication.Transcription and TranslationSlide38
Acridine orange was used to visualize RNA in the reconstruction
Channels throughout the rotavirus capsid in which allow the newly synthesized RNA to be exported
Transcribing DLP of RotavirusSlide39
Transcribing DLP of RotavirusSlide40
L-A virus is a fungal virus which contains 2 RNA dependent RNA polymerases on the inside of two of its capsid proteins
The RNA moves past the polymerases as it is synthesized and is exported through pores in the capsid
The capsid protects the RNA from degradation while allowing for the import of important metabolitesL-A VirusSlide41
L-A virus transcriptionSlide42
Virus Life Cycles in 3D - Description
The Art of Reconstruction In order to survive viruses must be able to do the following 1 Find a host cell it can replicate in 2 Bind to that cell 3 Enter the cell 4 Release its genome in order to replicate ID: 275658 Download Presentation
In order to survive, viruses must be able to do the following:. 1. Find a host cell it can replicate in. 2. Bind to that cell. 3. Enter the cell. 4. Release its genome in order to replicate. 5. Replicate its genome.
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