1、Viral Genome and StructuresLaboratory of Medical Molecular VirologyChang Liuv.163/special/opencourse/virology.htmlBreakthrough in 1950s The viral nucleic acid genome carries the information needed to replicate,build,and spread virions in the world.One of the building blocks of Molecular Biology T4,T
2、MVHershey-Chose experimentwith phage T4Fraenkel-Conrats work with TMVSeven Genome Types Either DNA or RNA Structurally diverse:linear,circular,segmented,gapped,single-stranded(+)strand,single-stranded(-)strand,single stranded(ambisense),double-stranded,some have covalently attached proteins,some hav
3、e cross-linked ends of double-stranded DNA RNA World hypothesisWhat information is encoded in a viral genome？Replication of viral genome Assembly and packaging of the genome Regulation and timing of the replication cycle Modulation of host defenses Spread to other cells and hostsInformation Not cont
4、ained in viral genomes No genes encoding the complete protein synthesis machinery No genes encoding protein involved in energy production or membrane biosynthesis No classical centromeres or telomeres found in standard host chromosomesThe Baltimore System Viral genome must make mRNA that can be read
5、 by host ribosomes NOT all(+)RNA is mRNA Each way has unique polymerase,primer,template and termination requirements Each virus family has its own characteristic genome strategySeven classes distinguished by genome replication strategiesds DNA,ss DNAds RNA,+ss RNA,-ssRNA,RetrodsDNA genomes The probl
6、em of replicating the ends of linear DNA molecules through the use of RNA primers.Circular ds DNA genomes that are replicated in the nucleusLinear ds DNA genomes that are replicated in the nucleusLinear ds DNA genomes that are replicated in the nucleusds DNA genomes that are replicated in the cytopl
7、asmssDNA genomesA basic problem with a ssDNA genome:RNA can only be made from a dsDNA template,ssDNA must be converted into dsDNA before mRNA is made DNA synthesis must precede mRNA productionLinear ss DNA genomes that are replicated in the nucleusRNA genomes Cells have NO RNA-dependent RNA polymera
8、ses(RdRp)to replicate the genomes of RNA viruses,or to make mRNA from RNA RNA virus genomes encode novel RdRp Polymerases produce both RNA genomes and mRNA from RNA templates+ssRNA,-ssRNA,dsRNA+ssRNA Hepatitis A virus,foot and mouth disease virus,and rhinoviruses which cause the common cold.The coro
9、naviruses which includes important veterinary viruses and the SARS virus.Hepatitis C virus.Yellow fever virus.Positive-strand RNA viruses that make no subgenomic mRNAsPositive-strand RNA viruses that make one or more subgenomic mRNAs-ssRNA RdRp Reassortment:Influenza virusNegative-strand RNA viruseA
10、mbisense RNA viruseDouble-stranded RNA(dsRNA)Many dsRNA genomes are segmented dsRNA cannot be translated by ribosomesds RNA virusesRetrovirus HIV HTLV Integrate into the host DNA HBVRetrovirusesHepadnavirusesStructure Nanometer:10-9 meters Atom:0.2-0.3 nm diameter Alpha helix in protein:1 nm diamete
11、r DNA:2 nm diameter Ribosome:20 nm diameter Poliovirus:30 nm Mimivirus:750 nmFunctions of virion proteins Protection of the genome Assembly of a stable,protective protein shell Specific recognition and packaging of the nucleic acid genome Interaction with host cell membranes to form the envelope Del
12、ivery of the genome Binding to host cell receptors Transmission of signals that induce uncoating of the genome Induction of fusion with host cell membranes Interaction with cell components to direct transport of genome to the appropriate sit Other interactions with host With cell components to ensur
13、e efficient infectious cycle With cell components for transport to sites of assembly With the host immune systemVirus particles are not inert structures Virions are metastable structures:have not attainted minimum free energy conformation Gained only when an unfavorable energy barrier is surmounted,
14、following irreversible conformational changes during attachment and entry Viruses are molecular machines that play active role in delivery of genome To be infectious,the particles must be metastable Must protect the genome(stable)Must come apart quickly on infection(unstable)An infectious virion is
15、a molecular machine Has moving parts and does workVirion structure and function Structure(the particles;the virion)Created by symmetrical arrangement of many identical proteins to provide maximal contact and non-covalent bonding Function(genome delivery)Made possible because the structure is Not per
16、manently bonded together Can be taken apart or loosened on infection to releaseThe tools of viral structural biology Electron microscopy X-ray crystallography Cryo-electron microscopy Nuclear magnetic resonance spectroscopy(NMR)TITLE:Artificial Nano“T4 Bacteriophage”Description:“T4 Bacteriophage”is
17、a virus like the robot in the living body.Artificial nano“T4 Bacteriophage”was fabricated by FIB-CVD on Si surface.Size of the artificial nano“T4 Bacteriophage”is about ten times as large as the real virus.It is made of Diamond-like Carbon.It is likely to begin to walk in the nano space!Magnificatio
18、n:25,000XInstrument:SII NanoTechnology Inc./SMI2050MS2Submitted by:Reo Kometani&Shinji Matsui(University of Hyogo)Structure of Reovirus Core Determined Via X-ray CrystallographyEnveloped viruses and coated vesicles cryo-electron microscopy and tomographyHerpes virus protein(red)docks with human cell
19、ular protein(white)UK scientists have used solution-state NMR spectroscopy for the first time to develop a 3D picture of a herpes virus protein interacting with a key part of the human cellular machinery.The study improves our understanding of how the virus hijacks human cells and could eventually l
20、ead to new targets for drug therapy.Principles of building virions:Symmetry is keyWatson and Crick did more than discover DNA structure 1956:pointed out that most virus particles were spherical or rod-shaped in the EM Knew particles were made with many copies of few proteins(genetic economy)Viral pr
21、oteins have structural properties that permit regular and repetitive interactions among themThey provide rules for“self-assembly”Rule 1:Each subunit has“identical”bonding contacts with its neighbors Rule 2:These bonding contacts are usually non-covalent Many capsid proteins can self assemble into“vi
22、rus-like particles”(VLPs)The HBV and HPV vaccines are VLPs made in yeastHelical symmetryEnveloped virions of RNA viruses with ssRNA genomes with helical capsids Paramyxoviridae(measles virus)Rhabdoviridae(rabies virus）Orthomyxoviridae(influenza virus)Filoviridae(Ebola virus)How can you make a round
23、capsid from proteins with irregular shapes?Clue1:All round capsids have precise numbers of proteins;multiples of 60 are common(60,180,240,960)(T number)Clue 2:Spherical viruses come in many size,but capsid proteins are 20-60 kDa averageTriangulation number,TQuasiequivalenceStructurally complex capsi
24、dsCapsid can be covered by host membranes:enveloped virions Enveloped virions are common,particularly those that infect animals Envelope is lipid bilayer derived from host cell Envelope acquired by budding of nucleocapsid through a cellular membraneAssembly of helical nucleocapsidsAssembly of isometric nucleocapsidsAcquisition of the lipid envelopeOther virion components Enzymes Polymerases,integrases,proteases Activators,mRNA degradation,required for efficient infection,mRNA Cellular components:Histones,tRNAs,myristate,lipid VIPERdb Viperdb.scripps.edu69谢谢！谢谢！
