Viral Structure Flashcards
what is a Capsid?
Viral container or shell proteins
what is a Nucleocapsid?
Situation where the capsid also contains the genome
what is an Envelope?
host derived lipid bilayer membranes enclosing nucleocapsids
do all viruses have an envelope and a capsid?
no
virion must be both —-
stable (outside cell) and unstable (within the cell), depending on stage of infectious cycle
How can you study viral structure?
- electron microscopy
- cryo-electro microscopy
- X-ray crystallography
- Nuclear Magnetic Resonance Spectroscopy (NMR)
how does e- microscopy work? disadv?
negative staining: stain samples with e- dense materials so e- is absorbed, but this might destroy ultrastructural features
how does Cryo- Electron Microscopy work?
- NO STAIN; structure preservation
- Flash freeze samples and image at very cold temperatures
- The freezing is the contrast. Aims to preserve structures.
- Use of computers to reconstruct images (3D reconstruction)
How does X-ray crystallography work?
must have ability of viral protein/virion to crystallize
has canyons (interact with host cell receptors) in 3D structure
How does Nuclear Magnetic Resonance Spectroscopy (NMR) work?
if protein doesn’t crystallize:
- Radiation emitted from a nucleus in a magnetic field
- Radiation emitted are measured by spectra
- Inherent property of certain nuclei to have a magnetic moment
SINGLE PROTEINS SEEN
how do the viral structural techniques compare in resolution?
X-Ray and NMR > Cryo- Electron EM > Electron Microscopy
how is NMR different from the viral structural biology techniques?
Cry- Electron EM , Electron Microscopy and X-Ray give full virion structures and NMR will only give viral proteins
virions are made of many copies of a
FEW PROTEINS (The viral genome’s coding capacity is limited)
why is protein subunits few and symmetrical?
If protein subunits on the surface are identical, then the contacts will be identical generating a symmetrical object
what are the two types of symmetry for viral proteins?
Helical symmetry:
- rod-shaped viruses
Polyhedral symmetry:
- round viruses
Rules of viral symmetry Provide the basis for —
assembly
what are the rules of viral symmetry?
- Each subunits had identical bonding contacts with neighbouring subunits
- Bonds between subunits are mostly via non-covalent interactions
why are bonds non-covalent?
need to break apart bonds to interact with host
how is viral symmetry used in vaccines?
(Self)-Assembly of coat proteins for Hepatitis B Virus and Human Papilloma
(Virus into Virus-Like Particles bc shell can give immune response)
Non-infectious but immunogenic and made in yeast! No Nucleic Acid
examples of helical symmetry>
- measle virus
- vesicular stomtits virus
- ebola virus
how does viral helical symmetry work?
protein subunt in nucleocapsid interact with an identical protein subunit in an identical manner and interact with viral genome. protein subunts can be 1+ protein types
viral helical symmetry in ebola virus?
- nucleoprotein directly surrounds the viral genome
- nucleoprotein is surrounded by viral protein making nucleocapsid
what was a discovery of round/spherical capsids?
Round capsids have a defined number of proteins in multiples of 60
what type of symmetry does a round capsid have?
icosahedral symmetry (20 triangle faces)
- 5-fold on vertice
- 2-fold edge
- 3-fold face
exception to round capsid axis of symmetry?
norwalk virus (larger virus)
Quasiequivalent
how does polivirus show round capsid symmetry?
3 viral proteins folded by protein (3CDpro) cutting extra strands so VPs arrange in each triangle face of sphere
where do viral envelops derive from?
host (after virion replication in host) by taking membrane from infected cell by BUDDING NUCLEOCAPSID
what is the envelope of virus made of? where does it come from?
use host machinery to make viral envelope gyloproteins that wait at host cell surface so that virion can pick them up as they leave the host membrane (lipid bilayer from host surrounds virus)
