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Emerging Viruses
Sue Delos CWA
Jan 23, 30, and Feb 6 2018
Part I IntroducCon to Virology What is a virus? Viral Lifecycle Common Needs Unique soluCons Transmission Routes ClassificaCon Methods of Visualizing Virion Components Capsid Structures Viral Envelopes
FuncCons of Structural Proteins FuncCons of Nonstructural Proteins
Part II Virus-‐Host InteracCons, Vaccines and Ihibitors
The Immune System Innate AdapCve Viral Countermeasures Vaccines Vaccines Improve Life Expectancy Dependence upon Herd Immunity Passive Vaccines AcCve Vaccines InacCvated Virus Subunit Vaccines Subunit Vaccines AnCvirals Requirements for success PotenCal Targets The Path of Drug Discovery The HIV experience The HCV experience
Part III Emerging Viruses
Zoonoses and Why They Occur Influenza, A Respiratory Virus Ebola, A Blood-‐Borne Virus Zika, A Mosquito Transmi[ed Virus
Emerging Viruses
Part I IntroducCon to Virology
What is a Virus?
A virus is an organism with two phases. What would you do if you were a parasite that could only reproduce inside a cell?
Cell
Stable parCcle
Extracellular
Intracellular A Virus is an Organism with Two Phases
Disassembly ReproducCon New, stable parCcle assembly and release
Common Needs 2 phases of viral lifecycle: extracellular and intracellular
• Find permissive cell • Bind cell • Penetrate membrane • Uncoat • Reprogram Cell for own replicaCon
• Establish replicaCon center
• Synthesize viral mRNA (transcripCon)
• Synthesize viral proteins (translaCon)
• Replicate genome • Assemble and mature virion
• Release stable virion (lysis or budding)
Structural Protein FuncCons Nonstructural Protein FuncCons
Unique SoluCons
ENTRY: • MulCple receptors • MulCple modes of entry • Surface proteins • Site of membrane penetraCon
• UncoaCng • ReplicaCon site • Assembly • Egress • (Cell-‐to-‐cell) transmission
Sites of Viral Entry into the Host
V. Raconelli, MID 31
Image credit: "PrevenCon and treatment of viral infecCons: Figure 1, by OpenStax College, Biology, CC BY 4.0. ModificaCon of original work by Mikael Häggström.
In humans
Viruses cause a wide range of misery
Viruses are Nature’s NanoparCcles
1 μM = 1000 nM
(too small to be observed by tradiConal microscope)
The Tools of Viral Structural Biology
• X-‐ray Crystallography (must have crystals)
• Electron microscopy (can see parCcles)
• CryoEM and Tomography (structures of flexible virions and proteins)
• NMR (structures of regions within protein)
• But most viruses and their proteins are flexible and do not crystallize
The Structural Proteins
Capsid FuncCons
• Encases and protects geneCc material • Contains the budding funcCon • Maintains stable structure during transit to new host/cell
• Undergoes orderly disintegraCon during entry and travel to replicaCon site
• For non-‐enveloped viruses, the capsid is the outer shell, contains the receptor binding site, and is the target for immune responses
(cores have icosahedral symmetry)
Icosahedral Capsid Structures
HPV 16 VLPs
Viral Envelopes • Membranes derived from Host Cell Membranes • Contain Viral Proteins termed Surface Proteins • Surface Proteins
– bind target cells – define internalizaCon pathways – Fuse viral and cellular membranes – Are targets of the immune response
• Because capsids usually contain budding informaCon, enveloped viruses are promiscuous for surface protein incorporaCon
Receptors Come in Many Forms
What we study: How enveloped viruses bind to, (enter), and fuse with cell membranes
Any thoughts on why we study this?
INFLUENZA HA: ConformaConal Changes During Fusion
Native: metastable structure
First change:
Head-group separation
Activated:
prehairpin
Post-fusion:
6-helix bundle
During fusion, fusion proteins convert from unique conforma:ons to 6-‐helix bundles
Common Viral Fusion Mechanism
Model is for a Class I fusion protein (flu HA, HIV Env, Ebola GP)
target membrane
virus membrane
Journal of General Virology (2002), 83, 1535–1545.
Influenza, VSV, SFV
Adenovirus(induces)
SV40, polyoma,
MLV?
Picornaviruses ?, Influenza,
Sendai?
Viruses Exploit All Modes of InternalizaCon
ReplicaCon
• DNA viruses replicate in the nucleus • Most RNA viruses replicate in the cytoplasm • Retroviruses reverse transcribe their RNA into DNA which then integrates into the host DNA for replicaCon
• Viral polymerases make mRNAs • Many viral proteins are synthesized as single polymer which must be cleaved into separate proteins for virus funcCon
• Unique viral proteins include reverse transcriptases (RT), integrases (IN), polymerases (Pol), and proteases
All Virions Complete a Common Set of Assembly ReacCons
FormaCon of individual structural units of the protein shell from one or several viral proteins
Assembly of the protein shell by appropriate, and someCmes variable, interacCons among structural units
SelecCve packaging of the nucleic acid genome and other essenCal virion components
AcquisiCon of an envelope
Release from host cell
MaturaCon of the virus parCcles
Common to all viruses
Unique to enveloped viruses
The HIV Life Cycle
All Steps in the Viral Life Cycle are Targets for IntervenCon
QuesCons?
Emerging Viruses
Part IIa Virus-‐Host InteracCons
The Two Arms of the Immune Response: Innate vs AdapCve Immunity
Innate • PrimiCve: In all mulCcellular
organisms • Directed toward classes of
molecules • Effectors broadly reacCve • No anamnesCc response • Effectors = epithelial cells,
phagocytes, endothelial cells, fibroblasts
Adap:ve • Only in vertebrates
• Directed toward specific epitopes on molecules
• Effectors highly specific • Memory persists • Effectors = lymphocytes,
AnCgen PresenCng Cells (APCs)
Interferons (IFN) are major components of innate immune response
NIH PublicaCon No. 03-‐5423
B-‐Cells Make AnCbodies Make Cytokines to SCmulate
Innate Immunity Steady-‐state Immune Readiness Regulate Immune Response SCmulate T-‐cells
NIH PublicaCon No. 03-‐5423
Three broad categories of T cells Helper T cells augment the immune response by recognizing the presence of a foreign anCgen and then sCmulaCng anCbody producCon and producing cytokines that “turn on” or acCvate other T cells. Regulatory T cells funcCon in an opposite manner: they dampen or turn off the immune response . Cytotoxic or “killer” T cells directly a[ack and destroy cells bearing anCgenic material.
Viral Interference with Early B-‐cell AcCvaCon
M. Kuka and M. Iannacone
, doi: 10.1038/nr, 2017.133i
Viral Interference with AnCbody ProducCon and High Affinity MaturaCon
M. Kuka and M. Iannacone, doi: 10.1038/nr, 2017.133i
M. Kuka and M. Iannacone, doi: 10.1038/nr, 2017.133i
M. Kuka and M. Iannacone, doi: 10.1038/nr, 2017.133i
QuesCons?