CSB351Y1 Lecture Notes - Lecture 30: Porosome, Membrane Fusion Protein, Lipid Bilayer Fusion
26 May 2018
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Lecture 30: Influenza Virus
Orthomyxoviridae have 3 influenza virus) – enveloped, exist in quasi-spherical (sneeze) or filamentous form (move), big
• 8 RNA fragments and 11 proteins produced
- First 3 fragments express replication complex proteins (PB1,2,A with PB1-F2 additional RF for apoptosis)
- HA, NP, NA M1/M2 (2 different transcripts from same genomic RNA), NS1/NEP or NS2 (alternative splicing)
- All forms elements of surface proteins
8 genome segment encodes 11 different proteins
• PB2 – binds Cap of mRNA (transcription initiation complex); PB1 – cleaves mRNA to make primer, RdRp activity
• PA – involved in transcription and replication
• HA – receptor binding, membrane fusion; NA – virus exit
• NP – nucleocapsid protein encapsidating viral RNA
• PB1-F2 – protein localized to mitochondria for apoptosis of host cell
• M1/M2 and NS1/NS2 RNA – alternatively spliced by cell
• M1 – interacts with NP, envelope and NS2; M2 – ion channel activity
• NS1 – reduces host cell response; NS2(NEP) – interacts with M1 to direct nuclear export of viral nucleocapsids
Influenza Ribonucleoprotein (NP)
• SSRNA coiled into hairpin, coated with NP monomers
• PB1,2,A form complex of RdRp (have karyophilic nuclear signals in their sequences, accumulate in nucleus)
- PB2 recognize +cleave type 1 cap structure of cellular mRNA and used as primers for vRNA (cap snatching)
• NP (arginine-rich + charged, preferable to bind to RNA) is major structural protein, responsible for helical
symmetry of RNPs – free NP essential for full length vial RNA synthesis
• HA go through post-transcriptional modification and contains principal antigenic determinants – variation in HA
glycoprotein manages host immune response (causes occurrence of outbreaks and failure for effective vaccine)
Replication in the nucleus - Orthomyxoviruses replicate in nucleus, complicating machinery required for viral replication
Stalk-pore hypothesis for membrane fusion mediated by HA
• Receptor-mediated endocytosis of virus, acidification of endosome → comformation change in HA → fusion
peptide insertion into target endosomal membrane → refolding of c-terminal region of HA → two membranes
pulled together (hemifusion) → fusion pore creation and dilation allowing release of viral nucleocapsids into
nucleus and contents of virus with cytoplasm
M2 – ion channel facilitating release of nucleocapsids (NP) from virion
• Low pH allows ion channels influx protons into virion, weakening M1 interactions and integrity of virus particle
• High pH, side change obstruct pore of M1, low pH, side chains rotate to allow RNP (8segments) to pass through
Cap Snatching – stealing caps from host RNA when going from uncapped – to +ssRNA (PA cleaves host mRNA in nucleus)
used to prime transcription and synthesize translatable viral mRNAs
• Receptor attachment (HA) → release of genome (M2 channel) → transcription → replication of viral genome
(PA,1,2, NP) and nascent nucleocapsids exported out nucleus (NS2) → virus assembly and budding (NA)
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Document Summary
Orthomyxoviridae have 3 influenza virus) enveloped, exist in quasi-spherical (sneeze) or filamentous form (move), big: 8 rna fragments and 11 proteins produced. First 3 fragments express replication complex proteins (pb1,2,a with pb1-f2 additional rf for apoptosis) Ha, np, na m1/m2 (2 different transcripts from same genomic rna), ns1/nep or ns2 (alternative splicing) Influenza ribonucleoprotein (np: ssrna coiled into hairpin, coated with np monomers, pb1,2,a form complex of rdrp (have karyophilic nuclear signals in their sequences, accumulate in nucleus) Replication in the nucleus - orthomyxoviruses replicate in nucleus, complicating machinery required for viral replication. M2 ion channel facilitating release of nucleocapsids (np) from virion. Low ph allows ion channels influx protons into virion, weakening m1 interactions and integrity of virus particle: high ph, side change obstruct pore of m1, low ph, side chains rotate to allow rnp (8segments) to pass through. Leptomycin b (prevents progeny vrnp from being produced) and tamiflu & relenza (prevent release inhibit na)
