Flavivirus E Protein and NS2B Protein Function Quiz
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Questions and Answers

What is the diameter of Picornaviruses?

  • ~30nm (correct)
  • ~40nm
  • ~20nm
  • ~50nm

    • What is the function of the 5’ NCR in Picornaviruses?

  • Forms the capsid shell
  • Contains an internal ribosome entry site (IRES) for translation initiation (correct)
  • Encodes the viral poly(A) tail
  • Binds to cellular receptors via loop regions

    • What is covalently bound to the 5’ end of the RNA in Picornaviruses?

  • '-' sense ssRNA genome
  • Viral protein VPg (correct)
  • Poly(A) tail
  • '+' sense ssRNA genome

    • How many copies of VP4 are present in a mature Picornavirus virion?

    <p>60</p> Signup and view all the answers

    Which protein is a precursor to E2, palmitoylated and glycosylated?

    <p>PE2</p> Signup and view all the answers

    Where are the structural proteins palmitoylated?

    <p>Golgi</p> Signup and view all the answers

    How does the virus exit the cell?

    <p>Budding</p> Signup and view all the answers

    What is the role of Flavivirus E protein domain III?

    <p>Receptor binding</p> Signup and view all the answers

    How do Flaviviruses enter cells?

    <p>Endocytosis within clathrin-coated vesicles</p> Signup and view all the answers

    What can antibody-dependent enhancement (ADE) cause in relation to dengue fever?

    <p>More severe disease like dengue hemorrhagic fever</p> Signup and view all the answers

    What is the role of the precursor membrane protein (prM) in Flaviviruses?

    <p>Associates with E protein to form a heterodimer, protecting E from premature conformational change</p> Signup and view all the answers

    What type of genome does Togavirus have?

    <p>'+' sense ssRNA genome</p> Signup and view all the answers

    How does the E glycoprotein of Togaviruses facilitate viral entry?

    <p>Binds to cellular receptors, leading to receptor-mediated endocytosis via clathrin-coated vesicles</p> Signup and view all the answers

    What is the mechanism of translation used by Picornaviruses?

    <p>Cap-dependent translation</p> Signup and view all the answers

    How are Picornavirus proteins initially synthesized?

    <p>As a single precursor polyprotein</p> Signup and view all the answers

    Where does replication of picornavirus RNAs occur?

    <p>In a multiprotein complex bound to cellular vesicles</p> Signup and view all the answers

    What conformational changes are involved in the entry of poliovirus RNA into the cytoplasm?

    <p>Major conformation changes</p> Signup and view all the answers

    How are Flaviviruses transmitted?

    <p>By arthropods</p> Signup and view all the answers

    What is the genome organization of Flaviviruses similar to?

    <p>Picornaviruses</p> Signup and view all the answers

    What is the diameter of Picornaviruses?

    <p>30nm</p> Signup and view all the answers

    How many copies of VP4 are present in a mature Picornavirus virion?

    <p>60 copies</p> Signup and view all the answers

    What is covalently bound to the 5’ end of the RNA in Picornaviruses?

    <p>VPg</p> Signup and view all the answers

    What is the function of the 5’ NCR in Picornaviruses?

    <p>Initiation of translation without a 5’ cap</p> Signup and view all the answers

    What type of genome does Picornaviruses have?

    <p>'+' sense ssRNA genome</p> Signup and view all the answers

    What is the likely function of the pyrimidine rich track in IRES elements?

    <p>Initiating translation at an internal site away from the 5’ end</p> Signup and view all the answers

    How do virions bind to cellular receptors in Picornaviruses?

    <p>Via depressions or loop region on their surface</p> Signup and view all the answers

    What is the role of VP4 in a mature Picornavirus virion?

    <p>Remains buried within the shell</p> Signup and view all the answers

    Where is the poly(A) tail located in Picornavirus RNA?

    <p>At the 3’ end of the RNA</p> Signup and view all the answers

    What is encoded by the Picornavirus genome but normally added by polymerases?

    <p>Poly(A) tail at the 3’ end of RNA</p> Signup and view all the answers

    What allows initiation of translation without having a 5’ cap in Picornaviruses?

    <p>'+' sense ssRNA genome</p> Signup and view all the answers

    Which cellular mechanism is disrupted by Picornavirus infection?

    <p>Cap-dependent translation</p> Signup and view all the answers

    What is the function of eIF-4E during Picornavirus infection?

    <p>It may be sequestered, leading to failed translation initiation</p> Signup and view all the answers

    What role do host cell proteins play in Picornavirus translation?

    <p>They bind to IRES and help with docking of 40S ribosomal subunit</p> Signup and view all the answers

    What is the initial form of Picornavirus proteins after synthesis?

    <p>Single precursor polyprotein</p> Signup and view all the answers

    What is the role of VPg during Picornavirus RNA synthesis?

    <p>Priming RNA synthesis by binding to uridine residues</p> Signup and view all the answers

    What is the fate of newly synthesized virions in Picornavirus infection?

    <p>They are released from the cell by lysis</p> Signup and view all the answers

    What inhibitory effect does Picornavirus infection have on host cell macromolecular functions?

    <p>Shut off host cap-dependent translation and RNA synthesis</p> Signup and view all the answers

    Which part of the capsid proteins forms a channel in the cell membrane during poliovirus entry into the cytoplasm?

    <p>VP4 and hydrophobic N-terminal of VP1</p> Signup and view all the answers

    What happens during virion assembly in Picornaviruses?

    <p>Cleavage of VP0 to VP2 plus VP4 occurs, followed by assembly into protomers and then pentamers.</p> Signup and view all the answers

    What is the fate of VP0 during virion assembly in Picornaviruses?

    <p>It is cleaved into VP2 and VP4 to form mature virion.</p> Signup and view all the answers

    What is the role of cellular vesicles in the initiation of picornavirus RNA replication?

    <p>They serve as nucleation sites (viral factories) for replication.</p> Signup and view all the answers

    Study Notes

    Flavivirus and Togavirus: Key Molecular Features and Entry Mechanisms

    • Flavivirus E protein is a type I membrane protein found as a dimer, with domain II forming a dimer interface and domain III used for receptor binding.
    • Synthesis of non-structural protein results in the establishment of active RNA replicase complexes, with RNA synthesis carried out on membranes in the cytoplasm.
    • Flaviviruses do not have a clearly identified cellular receptor, and entry is mediated by endocytosis within clathrin-coated vesicles.
    • Antibody-dependent enhancement (ADE) can cause more severe disease like dengue hemorrhagic fever, leading to shock, organ failure, and death if not treated.
    • Once the genome is in the cytosol, the RNA is bound by ribosomes and translated, producing polyprotein cleaved to produce precursor/functional protein.
    • The precursor membrane protein (prM) associates with E protein in the endoplasmic reticulum to form a heterodimer, protecting E from premature conformational change.
    • Togaviruses cause diseases in animals and humans, with symptoms ranging from rashes, high fever to joint pain and encephalitis.
    • Togaviruses are spherical enveloped particles with a fringe of projections, and the envelope contains 240 heterodimers of glycoproteins E1 and E2, while the capsid contains 240 copies of capsid proteins.
    • The Togavirus genome is a linear '+’ sense ssRNA genome, approximately 9.7-11.8kb in size, with both 5’ methylated cap and a 3’ poly(A) tail.
    • The E glycoprotein of Togaviruses binds to cellular receptors, leading to receptor-mediated endocytosis via clathrin-coated vesicles.
    • Once inside the cytoplasm, the RNA genome is released to be translated, and non-structural proteins catalyze the synthesis of full-length antigenome RNA.
    • The RNA polymerase of Togaviruses, comprising nsP1, nsP2, and nsP4, catalyzes the synthesis of full-length antigenome RNA.

    Viral Replication and Translation Processes in Picornaviruses and Flaviviruses

    • Picornaviruses use cap-dependent translation mechanism, but infection causes proteolytic cleavage of eIF-4G, hindering host cell translation
    • Picornaviruses hijack cellular translation by binding host cell proteins to internal ribosome entry site (IRES)
    • Picornavirus proteins are made as a single precursor polyprotein, autocatalytically cleaved into capsid proteins and non-structural proteins
    • Replication of picornavirus RNAs occurs in a multiprotein complex bound to cellular vesicles, utilizing negative RNA strand as a template for positive-strand synthesis
    • Entry of poliovirus RNA into the cytoplasm involves major conformation changes, leading to virion assembly through cleavage of VP0 to VP2 plus VP4
    • Picornavirus infection inhibits host cell functions and leads to the release of newly synthesized virions from the cell
    • Flaviviruses are transmitted by arthropods and cause important human diseases, with distinct genome organization resembling Picornaviruses
    • The flavivirus virion contains an envelope and 180 copies of M and E (envelope protein heterodimers) arranged with icosahedral symmetry
    • Flaviviruses have a linear '+' sense ssRNA genome capped at the 5' end, translated into a single long polyprotein undergoing proteolytic processing
    • Flavivirus genome organization is distinct from Togaviruses, despite similar virion morphology and transmission via arthropods
    • Flavivirus RNA structures at the 3' end are cleaved into non-structural and structural proteins, including capsid, prM, M, and NS3 proteins
    • NS3 protein of Flaviviruses is involved in polyprotein cleavage, RNA replication, and possesses nucleoside triphosphate and helicase activities

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    Test your knowledge of flavivirus E protein and NS2B protein functions with this quiz. Learn about their roles in receptor binding, membrane fusion, and viral polyprotein cleavage.

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