emma (L22)

Question 1

class of influenza virus and measles virus

Answer 1

influenza virus is a class 5 virus and a negative sense single stranded RNA virus
measles virus is also a class 5 virus so a negative sense single stranded RNA virus
the differences that influenza is a segmented genome into 8 different segments, well the genome of the measles virus is all as one segment wrapped around 1 ribonucleoprotein

Question 2

The Family Paramyxoviridae

Answer 2

respirovirus
morbillivirus
rubulavirus
avulavirus
aquaparamyxovirus
ferlavirus

Question 3

Morbillivirus: measles virus, rinderpest virus

Answer 3

it is closely related to rinderpest virus which is a cattle virus
this virus has been eradicated worldwide
it is not as variable and has an effective vaccine and no animal reservoir

Question 4

Measles virus (general info ?)

Answer 4

it doesn’t have an animal reservoir from which to re-emerge
if 95% of the population was vaccinated we could eradicate measles
if you don’t get vaccinated you’re affecting your health and the herd immunity

Question 5

measles: the disease

Answer 5

infection is in the lower respiratory tract
early symptoms can be easily mistaken for other viral infections
after the symptoms you get a distinctive rash that is easily recognisable as a measles rash
there are many complications like pneumonia encephalitis meningitis hearing loss blindness and and risk to unborn children
in rare cases there is a fatal brain disease
the infection has a long lasting effect on the immune system because even after you recover from measles years later you’re more susceptible to a secondary infection

Question 6

structure of viral particle

Answer 6

the virus causes the disease
the particles are similar to the flu but are 50% bigger
it is envelope and has glycoprotein spikes on the outside
under the envelope it has a protein shell of matrix
in the middle it has ribonucleoprotein structures
it is not segmented so it is 1 long genome segments wrapped around a ribonucleoprotein

two proteins on the surface of the virus the attachment protein hemagglutinin and the fusion protein
they are required for the measles virus to bind to the host cell
under the layer it has a matrix of proteins like the flu virus particle and under that there is the rnp complex (single-stranded negative sense RNA wrapped around the protein)

DIAGRAMS IN L22 S9-10

Question 7

Paramyxovirus ribonucleoprotein complex structure

Answer 7

L22 S11
long strand of -ve sense rna, wrapped up in nuclear protein
pol L has the polymerase activity and it has a phosphoprotein that is required for polymerase activity

L22 S18
RNP wrapped up in nuclear proteins
polymerase and phosphoprotein attached and they need to make some viral RNA to be translated into viral proteins

Question 8

attachment and entry proteins

Answer 8

Virus attachment protein:
- haemagglutinin (H) together with the fusion (F) protein

Host cell receptor:
- CD46
(present on all nucleated cells and used by laboratory and vaccine strains)
- signalling lymphocyte activation molecule (SLAM or CD150) (on T and B lymphocytes and antigen presenting cells)
- epithelial cell receptor (Nectin 4) (required for virus shedding in vivo)

Question 9

haemagglutinin protein

Answer 9

MONOMER
type 2 membrane protein = only has a single transmembrane domain, it’s cytoplasmic tail is at its c-terminus of the protein
globular head domain
the stork goes through the membrane
hg forms a dimer of dimers - forms a tetramer

DIMER
2 dimers bind to form tetramer
will attach to host cells by receptors (like SLAM or nectin 4)
that causes conformational change in attachment proteins and in Fusion protein

DIAGRAM IN L22 S13-14

Question 10

fusion protein

Answer 10

MONOMER
a type I membrane protein
it has a single transmembrane domain and its cytoplasmic tail is at its c terminus
haemagglutinin molecule of the flu is synthesized as a single polypeptide but then the host cell proteases cleave it into two polypeptides in order to release the Fusion peptide
same thing happens with the measles fusion protein
it is translated as one polypeptide and then the protease in the golgi of the infected cell will cleave the protein, leaving the Fusion protein on the n-terminus

TRIMER
fusion protein forms a trimer and looks similar to the hemagglutinin of flu

when measles virus attaches to a host cell its h protein binds to the receptor, causes a conformational change in h&f which causes the Fusion peptide to insert into the host cell plasma membrane

DIAGRAM IN L22 S15

Question 11

difference in entry between flu and measles

Answer 11

FLU: taken into the endosome and causes acidification, the influx of proteins causes conformational change then the membranes fuse and the RNPs are released.
MEASLES: virus isnt taken into endosomes, neutral pH, happens at the plasma membrane so the Fusion peptide inserts itself into the plasma membrane causes a fusion of the plasma membrane and the cell membrane, this will release the one RNP complex of the entire genome into the cytoplasm

Question 12

Paramyxoviridae genome

Answer 12

all very similar - have 6 same genes in the same order on the genome

NP nucleoprotein - wraps up the genome
P phosphoprotein - along the ribonucleic protein too
M matrix - structural protein, forms the shell
F fusion and H haemaglutinin - for entry into host cell
L Lpolymerase - not so much is needed

Question 13

sense of viral genome

Answer 13

these are -ve sense viruses so we write them as 3’ end to 5’ end and transcribed as 3 to 5’ to produce proteins in 5’ to 3’ direction
order of genes is very important
most abundant at 3’ end and least abundant at 5’ end

Question 14

how does measles make its mrna

Answer 14

its template (-ve sense) is one strand of rna
has 6 genes and makes different proteins
at 3’ end of genome, there is a specific sequence that the L polymerase recognises and uses it as a template (and uses phosphoprotein as cofactor)
scans along the genome template until it finds a gene start sequence
each gene has a gene start and end sequence
this polymerase will make a capped mrna

PROCESS L22 S22-29

Question 15

Transcription or genome replication?

Answer 15

1. Transcription – production of a gradient of viral mRNA transcripts.
2. Translation of viral proteins – N proteins accumulate.
3. N proteins encapsidate newly synthesized RNA – L polymerase bypasses gene end signals and transcribes entire genome to give antigenome RNA.
4. Antigenome is the template for replication of new genome RNA.

Question 16

where are the proteins translated in host cell

Answer 16

H and F - these are translated on ER bound ribosomes because they are membrane bound proteins (follow the secretory pathway from er to membrane)

other proteins are translated on free ribosomes in cytoplasm
nuclear proteins encompass the viral rna and antigenome rna
associates with the L and P proteins

Question 17

Measles virus NP protein production

Answer 17

Nucleoprotein (N): translated on non-membrane-bound ribosomes.
Associates with the P and L proteins and genomic RNA to form the ribonucleoprotein (RNP) complex.

Question 18

Measles virus P protein production

Answer 18

Phosphoprotein (P): translated on non-membrane-bound ribosomes.
Associates with the N and L proteins and genomic RNA to form the RNP complex.

Question 19

Measles virus L protein production

Answer 19

Large (L) polymerase protein: translated on non-membrane-bound ribosomes.
Associates with the N and P proteins and genomic RNA to form the
RNP complex

Question 20

Measles virus M protein production

Answer 20

Matrix (M) protein: translated non-membrane-bound ribosomes.
Associates with the RNP complex to move through the cell.
Associates with the plasma membrane and the cytoplasmic tails of the H and F proteins at the plasma membrane.

Question 21

Measles virus H protein production

Answer 21

translated on membrane-bound ribosomes.
Forms a dimer while being translocated through the ER where it is glycosylated. Ultimately located on the plasma membrane

Question 22

Measles virus F protein production

Answer 22

translated on membrane-bound ribosomes. Glycosylated after translation.
Forms trimer in Golgi then cleaved by furin enzyme
to F1 and F2 in the trans Golgi compartment. Ultimately located on the plasma membrane.

Question 23

leaky scanning

Answer 23

leaky scanning leads to translation of the C protein

to produce the c protein, the virus uses leaky scanning (same in flu to make PB1F2)
first AUG in this P mrna si the start codon to make the P protein
some ribosomes bypass this aug ad keep scanning down until they find the next aug
if they start translating at this aug, they start making the C protein (completely different to P protein)
c (only 186 amino acids) protein is different to the p protein (507 amino acids)

Question 24

protein expression from the measles virus P mRNA

Answer 24

V protein has the same N terminus as the P protein but a different C terminus
it look reminiscent of the PAX protein in flu (made by ribosomal frameshifting)
here, we see a frameshift too which is why we have a different C terminus, but the mechanism is different (it’s not ribosomal frameshifting, actually is rna editing)

to make this protein, in transcribing the P mrna, the L pol inserts an extra G nucleotide at the specific +1G position

Pmrna has this sequence in genome and so that sequence of aa
but occasionally while l pol is making the rna, it inserts the extra G which changes the reading frame of the codons downstream of that, and you get a diff aa sequence at the C terminus and so this is how you get the V protein

Vmrna is the same as Pmrna until it gets to the +1G red site

Question 25

measles virus exit

Answer 25

BUDDING AT THE CYTOPLASMIC MEMBRANE

more simple than the flu (because there are not 8 segments that need to get into viral particle)
has H and F proteins that accumulate at specific areas of the cell membrane
matrix proteins recognises the cytoplasmic tail of these proteins and forms a shell underneath the membrane. matrix protein also binds the viral RNP complex (only one in measles)

once all together, the particle starts to pinch off to end up with viral particles (budding)