Lecture 6 - Virus Structure

Icosahedral viruses can accomodate different type of genomes (RNA, DNA, ss, or ds) Two are most common.

(+)ssRNA ssDNA

Helical (4, 1 ex)

- single capsomer type - helical structure - usually ssRNA - (-) DNA attracts (+) subunits ex: tobacco mosaic virus (TMV)

Virons must be

1. correctly assembled 2. escape host 3. withstand extracellular environment 4. attach and enter another host 5. release viral genome

Virus capsid structures (4)

1. helical 2. icosahedral 3. enveloped 4. complex

4 steps to Bacteriophage T4 infecting E.coli bacteria:

1. landing 2. pinning 3. tail contraction/ penetration 4. DNA injection

Viruses penetrate host cells two ways (2)

1. membrane fusion at cell surface 2. receptor mediated endocytosis

Icosahedral shape stability (4)?

1. strength of icosahedral 2. resistance to shear forces (no projections) 3. tight package 4. genetic economy - can be built from few repeating subunits

Icosahedron is a polyhedron w/

20 faces, 30 edges and 12 vertices

Viruses can get into cells not just w/ proteins! 2 examples

Influenza w/ sialic acid (sugar) Vesicular stomatitis virus w/ membrane lipids

Viral glycoproteins are modified w/ host sugars. Two types of glycosylation (2)

N-glycosylation O-glycosylation

After contraction of tail sheath and penetration of OM. What lysosome degrades peptidoglycan layer?

T4 lysosome

Chemical damage example (1)

UV irradiation

Virion =

a complete, infectious, virus particle

O-glycosylation =

adding sugar chain on serine/thereonine

N-glycosylation =

adding sugar chains on amide nitrogen of asparagine

In eukaryotic cells 2 stages

attachment (electrostatic revertible and tight irreversible on receptor) and penetration

Can decontaminate surfaces w/ icosahedral viruses w/ (1)

bleach

Enveloped viruses have protein of cells surface because when they bud off....

can't bud off a totally protein free membrane

Capsid subunits are called (1)

capsomers

Bacteriophage T4 is a (1) type of virus?

complex, dsDNA

At least 3 long tail fibers bind before the short tail fibers bind. The short tails bind to (1)

core region of the host cell LPS

Diversity of viruses can be explained due to the "blank" challenges they are presented w/

different

Destroy 1 capsomer and result (1)

doesn't destroy infectivity of whole particle

Naked icosahedral viruses (compared to envelopped) are common of what type of viruses?

enteric!

Stability of helical capsids very high. Will self- assemble in absent of information. Particle is in its (1)

free energy minimum state

Influenza virus envelope has two important glycoproteins (what and function)

hemagglutinin (HA) - a lectin that sticks to sialic acid receptor on cell for binding and entry neuraminidase (NA) - enzyme that cleaves sialic acid allowing virus to be released from host

Staple enveloped virus example (6)

herpes simplex virus ebola rabies HIV influenza KSHV/HHV-8

Influenza virion has two viral proteins but also many...(1)

host proteins

Icoshedral capsides are typical of infecting (1)

humans, animals

Helical capsid typically don't infect...(1)

humans, usually plant

Enveloped viruses advantage (1)

immune recognize as self, glycosylation of virus proteins shield viral epitopes from immune system

After peptidoglycan layer is degraded then...

inner membrane degraded. Finally phage DNA delivered to cytoplasm.

When the short protein (on base plate) is attached it is at what stage?

irreversible

Capsids need to be strong but able disable. This is called? (1)

metastable

Virus particle =

molecular structures that package virus genomes in infected cells and transmit them to new host cells i.e: doesn't take into account infectious nature

Icosahedral unlike helical capsids can have (1)

multiple capsomer types

Enzymatic damage example (1)

nucleases from dead/leaky cells from host defense

Long tail fibers recognize 2 bacteria structure on PM.

outer membrane protein C (OmpC) LPS

Nucleic acid genome is fragile. Capsids protect from (3) damages

physical chemical enzymatic

Examples of Icosahedral (3)

poliovirus, adenovirus, hepatitis A virus

Complex viruses not purely helical or icosahedral but also have extra structures such as (2)

protein tails, complex outer wall

When the long protein tail fibers attach the binding it is at a what stage?

reversible

Capsids are =

rigid, symmetrical container for viral genomes

Physical damage example (1)

shearing by mechanical forces (ex: blood stream)

Icosahedral structure advantageous to enteric infection because of their inherent (2)

strength, resistance to acid (low pH)

Helical capsids can only be as long as...

the RNA they store.