Virology - Exam 2

average size of proteins in spherical viruses

20-60 kDA

What did Caper & Klug

From Watson and Crick findings:

-capsid subunits tended to be arranged as hexamers and pentamers

-number of capsid subunits followed multiples of 60

virus examples with icosahedron symmetry

1. Adeno-associated virus 2 (parvovirus)

- 25 nm diameter

- 60 copies of single capsid protein

2. Calicivirus

- 42 nm diameter

180 copies of single capsid protein

what can viral proteins interact with

viral envelope proteins

delivery of viral genome

-bind host cell receptors

-uncoating of the genome

-fusion with cell membranes

-trasport of the genome to the apporpriate site

function of viral capsid & virion particles

1. Delivery of Genome

2. Protection of the genome

What did Watson and Crick find about viral structures?

-most viral particles are spherical or rod-shaped

-particles are made up with many copies of few proteins

symmetry rules

1. Each subunit has "identical" bonding content with neighbors

2. bonding contents are non-covalent (usually)*

*reversible

viruses with helical nucleocapsids

many (-)RNA viruses:

• Paramyxoviridae - measels virus, mumps virus

• Rhabdoviridae - rabies virus

• Orthomyxoviridae - influenza virus

• Filoviridae - Ebola virus

Icosahedral symetry

round capsids have what precise number of proteins?

multiples of 60: (60, 180, 240, 960)

virion

the complete, infectious form of a virus outside a host cell designed for transmission of the nucleic acid genome among hosts or host cells

capsid

protein shell surrounding genome

structural unit

(protomer, asymmetric unit)

-unit from which capsid is built, one or more subunits

subunit

single folded polypeptide chain

icosahedron

solid unit with 20 faces that are equilateral triangles

how many faces in icosahedron

20

What is Triangulation number?

- # of facets (smaller triangles) per triangular face of an isocahedron

- each facet contains a capsid protein multimer

example of T=4 virus

T equation

T=h^2 + hk + k^2

what happens if capsid contains more than 60 subunits

each unit occupies a quasieequivalent position

quasiequivalent position

noncovalent binding properties of the subunits in different structural environments are similar but not identical

lipid envelope

-derived from host cell membranes

-acquired by budding of capsid through cellular membrane

-can be any cell membrane but its virus specific

glycoprotein

protein with sugar (oligosaccharide)

lipid envelope benefits

hides the viral nucleic particles from cells (almost like camouflage)

Viral Infectious cycle

1. attachement

2. entry

3. genome replication

4. assembly

5. release

how does capsid protect genome

it acts as a stable, protective protein shell

Main issue/dilema with the way DNA and proteins are in viruses

DNA is bigger than protein:

Which is bigger, DNA or protein?

DNA:

-three nucleotide (codon) for every amino acid

how do viruses practice genetic economy?

they make multiple copies of the same protein

explain helical symetry in rod-shaped viruses

identical protein subunits are used

can viruses diffuse through plasma membrane?

No, they are too large

what do viruses rely on for atatchment

brownian motion, diffusion, and electrostatics

How do virions attach to plasma membrane

1. adhere to the cell surface by electrostatic interactions (non-specific binding)

2. attach to specific receptor molecule(s) on cell surface

what's true about viruses and their ability to bind to receptors

different viruses can bind to the same receptor and viruses in the same family can bind to different receptors

viruses that bind to same receptor

1. Adenovirus(dsDNA) and Coxsackie virus B3 (+RNA)

2. swine herpesvirus, pseudo-rabies virus, poliovirus

viruses that bind to multiple different receptors

1. rhinoviruses (at least 3)

2. retroviruses (at least 16)

method of which noneneveloped viruses bind to plasma membrane

they use capsid surface proteins (projections)

how many receptor binding sites do icosahedral symmetry provide

60

where can receptor binding occur

various different places

viruses that need a co-receptor

Adenovirus --> CAR receptor and integrin

viruses that are enveloped and bind via transmembrane glycoproteins

HIV & influenza

HIV binds to what 2 receptors

CD4 and CXCR4/CCR5

CCR5 mutation leads to what percentage of people resistant to HIV?

about 7%

what did they do to the CRISPR babies?

deleted CCR5 for HIV resistnace

what does the receptor for SARS-CoV2 do

its an angiotensin converting enzyme

How SAR-Cov2 get RNA into cell?

through the fission of SARS-Cov2 into the cellular membrane, it creates a "pore" that allows RNA to enter the cell through

What are the diff. influenza types

A, B, C, D

what type of influenza causes seasonal epidemics

A, B

what type of influenza causes mild ilness

C

what influenza causes illness in cattle

D

how many people died from infleunza from 2017-18 in US

80,000

how many people die from influenza worldwide each year

300,000-600,000

what surface proteins are used to classify influenza A subtypes

hemagglutinin (HA)

neuraminidase (NA)

HA subtypes

H1-H18

NA subtypes

N1-N11

H1N1

swine flu

N5N1

bird flu

how is influenza A named

based on off HA and NA surface proteins

why is there so much genetic diversity in influenza

reassortment occurs: two different flu viruses infect the same cell —> genetic diversity

what’s the main cause of the 2009 flu pandemic strain

reassortment between human, avian, and swine flu viruses

what is the receptor for influenza viruses

sialic acid (SA)

human flu strains prefer what sialic acid receptors, while avain flu strains prefer what receptor

alpha (2,6) | alpha (2,3)

where is apha (2,6) located, what about alpha (2,3)

trachea epithelial cells in the human respiratory tract, lower tract epithelial cells in the human respiratory

why does avian flu not transmit as efficiently

because of the different in sialic acid receptors as well as where the receptors are located at

avian flu GOF research

how many plasmid transfection did it take to make the mutant avian flu

8

location of where mutations occured in HA protein

first is human strain, second is avain:

things to note: blue line is binding ability of a2,3 receptors while red line is binding ability of a2,6 receptors

just 4 mutations were necessary and virus became more infectious

images of lung epititheal cells (blue) with influenza virus (green) and how it is able to bind to the cells

the main thing to know is that the researchers put a ferret that was infected with mutant strains of influenza in a cage next to a healthy ferret and saw how many ferrets became infected with influenza (the strain with more mutations were more infectious

why were ferrets the animal model of choice for the infleunza GOF research?

because ferrets have receptors for both a(2,6) as well as a(2,3)

Figure 4 | Respiratory droplet transmission of H5 avian–human reassortant viruses in ferrets.

Polykaryon formation by HeLa cells expressing wild-type or mutant HAs after acidification at low pH.

polykaryon —> multinuclear cell or individual, in this case, its the the virus

Pathological analyses of H5 avianhuman reassortant viruses.

summary of GOF influenza research

researches infected ferreets and added mutatinos to see what mutations in the avian flu are necesarry for it to become infectious in humans, in the end, the interesting thing that they found was that the more infectious is was in humans, the less deadly it was —> most likely because receptors that make influenza infectious in humans are located in the upper tract of the human respiratory system

mortality rate children before vaccinations were a thing (<5 years old)

30%

what percentage of deaths in Michigan were children

35%

how long does vaccination go back

1000 years

what did Jenner do? (vaccination)

1796 - made the first “vaccine” using cowpox (later found to be horsepox) to prevent smallpox

• saw that milkmaids with cowpox didn’t get small pox so got the puss of the spots in these milkmaids and put under the skin of a child and exposed them to small pox

what did Pasteur do? (vaccination)

1885 - developed the first rabies vaccine

• mother took child who was bitten by rabid dog to Pasteur who tested out his vaccine

what vaccines were developed in the 1930s

yellow fever and influenza vaccine was developed

Faroe Islands

an example of “natural” immune memory:

• 1781: measles outbreak

• 1846: 2nd Measles outbreak

  • people who were around in the first outbreak didn’t get measles in 1846 —> immune memory lasts a long time adn can be maintained without re-exposure to virus

When was innactive Polio vaccine introduced

1955

when was oral polio vaccine introduced

1963

measles vaccine —> what is it and what does it prevent

MMR vaccine: prevents SSPE (subacute sclerosing panencephalitis)

what other do vaccines provide other than protection from pathogen

sometimes they have other effects:

• rota virus —> vaccination linked with the drop of infant type I diabetes

What happened to the states where there was a high number of NME (nonmedical exemptions) ? In 2016 to 2017

There were high cases of measles that arised in 2019

Passive vaccination

instill into the products of the immune response (antibodies or immune cells) into the recipient

• short term immunity

What’s an example of passive immunity

Mothers passing antibodies to children

vaccine examples of passive vaccines

• rabies —> rabies immune globuline (RIG)

• ebola —> Zmapp

• RSV —> new vaccine approved in August (for infants <8 months old entering RSV season)

• COVID-19 (some vacciens (monoclonal antibodies)

what are non-passive vaccines

recipient receives a modified form of the pathogen or material derived from that pathogen that induces immunity

• long term protection

Adaptive immunity and vaccines

otherwise known as acquired immunity —> basis for effective immunization and involves immune responses that are specific to an antigen

• tailored to specific pathogen

• takes more time than innate response

• has memory

vaccines make sure that adaptive immunity is “ready to go”

what makes up adaptive response

1. humoral response (antibody)

2. cell-mediated response (helper and effector cells)

neutralizing antibodies

essentail defense agains many virus infections

• interferes with many different processes of virus trying to infect cell

examples of who neutralizing anitbodies help

• secretory antibodies at mucosal surfaces block entry into host

• neutralizing antibodies are used to treat rabies infection and now Ebola

what are CTL and what do they do

ctotoxic T-lymphocyte

• they kill infected cell

  • cell presents antigen or markers for CTL to identify, and then secretes toxins to kill the cell

how do CTLs kill cell

1. transfer of cytoplasmic granules containing perforin and granzymes (proteases that cause apoptosis

2. apoptosis

vaccines need to be….

1. safe

2. efficacious

3. practical

live attenuated vaccine examples

• adenovirus

• influenza

• measles

• mumps

• Rubella

• polio (live)

• varicella

• yellow fever