Lecture 2. Introduction to Viral Replication - Influenza Virus Replication 1 Flashcards
What happens in the attachment stage of viral replication?
Binding to a cell surface receptor; primary determinant of tropism (specificity of what types of cells/what organism a virus can infect)
What happens in the entry stage of viral replication?
Enveloped viruses fuse with cell or endosomal membrane
Non-enveloped viruses endocytosed
What happens in the uncoating stage of viral replication?
Structural proteins of virus disassemble to release genome
What happens in the biosynthesis stage of viral replication?
Genome is replicated
Viral proteins are synthesised
What happens in the assembly stage of viral replication?
Viral proteins form particle structure; genome is packaged; envelope may be acquired
What happens in the exit stage of viral replication?
Viral particles leave cell by budding (normally enveloped viruses), exocytosis, cell lysis; virion maturation may occur (HIV)
How do viruses synthesise their proteins from mRNA?
Viruses use host cell ribosomes and translation machinery
Because different viruses have different genomes, what have the different viruses developed in terms of replication?
They therefore have different strategies for genome replication and synthesis of mRNA
What do almost all viruses carry?
Their own polymerases
What can viral dsDNA be?
Linear e.g. Adenoviruses
Circular e.g. Herpesviruses
Gapped e.g. Hepatitis B virus
What can viral ssDNA be?
+ve or –ve sense e.g. Parvoviruses
What can viral dsRNA be?
Segmented e.g Rotavirus
Non-segmented e.g yeast L-A virus
What can viral ssRNA be?
+ve sense e.g Poliovirus, HIV
-ve sense segmented e.g Influenza
-ve sense non-segmented e.g Measles
Ambisense (some genes coded in one direction and others in a different direction) e.g Arenaviruses
What are Baltimore class 1 viruses, how do they replicate and how are they transcribed?
dsDNA viruses (e.g Herpesvirus)
Replicate self using viral DNA polymerase
Transcribed into +ve sense mRNA by post-cell RNA polymerase
What are Baltimore class 2 viruses, how do they replicate and how are they transcribed?
ssDNA viruses (e.g Paroviruses)
Replicate using dsDNA intermediate from host DNA polymerase
Transcribed into +ve sense mRNA by post-cell RNA polymerase
What are Baltimore class 3 viruses, how do they replicate and how are they transcribed?
dsRNA viruses (e.g Rotavirus)
Replicate using +ve sense mRNA intermediate from host
Transcribed into +ve sense mRNA using own RNA polymerase
What are Baltimore class 4 viruses, how do they replicate and how are they translated?
ssRNA +ve sense viruses (e.g Coronavirus, Poliovirus)
Replicate using dsRNA replicative intermediate
Can be translated directly into protein
What are Baltimore class 5 viruses, how do they replicate and how are they transcribed?
ssRNA -ve sense viruses (e.g Influenza)
Replicate using dsRNA replicative intermediate
Transcribed into +ve sense mRNA using -ve sense ssRNA genome as a template
What are Baltimore class 6 viruses, how do they replicate and how are they transcribed?
ssRNA +ve sense viruses (e.g HIV)
ssRNA reverse transcribed into dsDNA intermediate
This dsDNA intermediate is often used as a template for transcribing the original +ve ssRNA and also +ve mRNA
What are Baltimore class 7 viruses, how do they replicate and how are they transcribed?
dsDNA (e.g Hepatitis B virus)
Gapped dsDNA
+ve sense mRNA acts as a template for dsDNA replication
Transcribed into +ve sense mRNA through utlising viral RNA-dependent DNA polymerase (reverse transcriptase)
Why study viral replication?
Knowledge of all stages of the life cycle of a virus
How a virus interacts with cellular proteins and structures
Information about viral enzymes
How a virus causes disease
How can we stop a virus and what should be targeted?
A virus replicates inside cells, using host cell proteins.
Can’t target host proteins with drugs without side effects.
Can sometimes target viral enzymes/processes.
What are examples of viruses that have successful drug treatments?
Herpesviruses and HIV
Only possible due to knowledge of the life cycle
What are examples of Baltimore class 5 virus families with segmented genomes?
Orthomyxoviruses
Arenaviruses
Bunyaviruses
What is an example of an orthomyxovirus?
Influenza virus
What is an example of an arenavirus?
Lassa fever virus
What are examples of bunyaviruses?
Maguari virus
La Crosse virus
What are examples of class 5 virus families with non-segmented genomes?
Paramyxoviruses
Rhabdoviruses
Filoviruses
What are examples of paramyxoviruses?
Measles virus
Mumps virus
Sendai virus
Respiratory syncytial virus
What are examples of rhabdoviruses?
Vesicular stomatitis virus
Rabies virus
What are examples of filoviruses?
Ebola virus
Marburg virus
What are examples of past influenza pandemics?
Spanish flu - 1918 - 25,000,000 deaths
Asian flu - 1956 - 70,000 deaths
Hong Kong flu - 1968 - 34,000 deaths
Swine flu (H1N1) - 2009 - +450 deaths
What strain of influenza are scientists worried about and why?
H5N1 (type of avian flu) - worried it might mutate and become transmissible in humans (doesn’t transmit well into humans currently, but responsible for +250 deaths since 2003)
What is it important to remember about virus structures?
Heterogeneity between structures (some look model, some can have protrusions, some are amorphous shapes)
What are the two proteins within the surface of influenza and which one is more common?
Haemagglutinin (HA, trimer and more common)
Neuraminidase (NA, tetramer and less common)
How are influenza strains classified?
By the level of HA and NA on their surface (e.g H1N1 vs H5N1)
In the structure of an influenza virus, what is M2?
An ion channel that is involved with entry of the virus
In the structure of an influenza virus, what is M1?
The matrix protein that forms the virus particle structure
What is the ribonucleoprotein located within influenza?
The genome tail of the -ve strand ssRNA (comprised of 8 parts) is wrapped up in nucleoprotein and has a copy of the viral polymerase attached to it. Each segment is a singular ribonucleoprotein (8 RNPs)
What are the three polymerase subunits that bind to the ends of the influenza RNP, forming what?
Polymerase basic protein 1 (PB1)
Polymerase basic protein (PB2)
Polymerase acidic protein (PA)
Three subunits form the viral polymerase
What do the different genome segments of influenza virus encode?
Different proteins, some encode a singular protein, some encode more than one (have to encode for more than one open reading frame)
What is the receptor for influenza on the epithelial cell?
Sialic acid
What is the abridged process of influenza entry into the cell?
HA on influenza attaches to epithelial cell (sialic acid receptor)
Conformational change as influenza cell membrane starts to invaginate epithelial cell
Virus particle engulfed into an endosome
How is sialic acid linked to galactose in the human respiratory epithelium?
α(2,6) linkage, which human virus strains (e.g H1N1) preferentially bind to
How is sialic acid linked to galactose in the duck gut epithelium?
α(2,3) linkage, which avian virus strains (e.g H5N1) preferentially bind to
How does the influenza virus uncoat and enter the cell?
HA trimer binds to sialic acid and virus is endocytosed by an endosome
Inside of endosome becomes acidified - low pH changes conformation of HA to expose fusion peptide (sticks into endosomal membrane)
Acidification of the virus particle via M2 causes fusion of membranes (brought closer together), and release of vRNPS from M1
RNPs head for the nucleus
