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    the diagram shows an hiv particle. what is the function of the glycoproteins on the outside of the virus?


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    Envelope protein attaches HIV to the cells that it infects and powers fusion of the virus with the cell membrane

    HIV Envelope Glycoprotein

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    Viruses are faced with a tricky problem: they need to get inside cells, but cells are surrounded by a protective membrane. Enveloped viruses like HIV and influenza, which are themselves surrounded by a similar membrane, solve this problem by fusing with the cell membrane. The envelope glycoprotein (Env) of HIV performs the many complex steps needed for membrane fusion. First, it attaches itself to proteins on the surface of the cell. Then, it acts like a spring-loaded mousetrap and snaps into a new conformation that drags the virus and cell close enough that the membranes fuse. Finally, the HIV genome is released into the cell, where it quickly gets to work building new viruses.

    Env Synthesis

    The Env glycoprotein is found on the surface of HIV, forming little knobs composed of three identical subunits. It is covered with carbohydrate, with about 81 glycosylated sites on each trimer. It is encoded in the HIV genome as one long protein, which is called gp160 (gp is short for "glycoprotein"). Then, as it is transported to the infected cell's surface, the many carbohydrates are added and it is cleaved into two pieces, called gp120 and gp41. Then, it is incorporated into the virus as it buds from the cell surface.

    Solving the Structure of Env

    The HIV Env glycoprotein has been particularly difficult to study for several reasons: it is covered with flexible carbohydrates, it is normally bound to membranes, and it is intrinsically flexible, since it needs to adopt several different shapes during the process of membrane fusion. Researchers have solved this problem by cutting off all the flexible and sticky bits and studying the rigid core of the molecule. The structure shown here, from PDB entry 4nco , is one of the most complete structures solved so far. It includes gp120 (yellow) with lots of carbohydrate (orange), and the outer portion of gp41 (red). The same molecule has also been studied by electron microscopy in PDB entries 3j5m and 4cc8 ). The structures also have broadly-neutralizing antibodies bound to Env (not shown here) that are being studied for vaccine design--these will be discussed in more detail next month.

    Cellular Receptors

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    The gp120 portion of Env glycoprotein is in charge of finding cells and attaching to them. It binds selectively to CD4 protein (shown here in blue), which extends from the surface of cells. Then, a shift in the shape of gp120 allows it to bind to a second cellular co-receptor, strengthening the attachment and leading to the fusion event. An early structure, from PDB entry 1gc1 , revealed the interaction of CD4 with gp120 by using a truncated form of the viral protein, which had several of the flexible protein loops shortened to something more manageable. The illustration shown here was created by overlapping this groundbreaking structure onto the more recent structure of the trimer, showing how the whole thing might be situated during the process of attachment.

    Exploring the Structure

    Image JSmol 1

    The gp41 portion of Env glycoprotein gets the virus inside the cell after gp120 attaches to the surface. As with the influenza hemagglutinin protein, a large change in the shape of the protein is thought to drag the viral membrane and cell membrane into close proximity. The formation of a distinctive helical bundle is important in both viruses, as shown on the left in a structure of the extracellular portion of the SIV gp41 protein (PDB entry 2ezo ). Researchers have developed new drugs that target this interaction and mimic part of the helical bundle, blocking the formation of this important structure. The image on the right shows one of these drugs (in green) bound to the inner bundle of gp41 helices (in red), from PDB entry 3vie . To explore these structures in more detail, click on the image for an interactive jmol.

    Topics for Further Discussion

    Many structures for fusion-inhibiting drugs are available in the PDB--try searching for "HIV-1 fusion inhibitor."

    Take a look at the EMDataBank to see studies of the whole Env glycoprotein, such as these structures of HIV Env and SIV Env

    Related PDB-101 Resources

    Browse Viruses Browse HIV and AIDS

    Browse Integrative/Hybrid Methods

    Browse Drug Action


    4nco: J. P. Julien, A. Cupo, D. Sok, R. L. Stanfield, D. Lyumkis, M. C. Deller, P. J. Klasse, D. R. Burton, R. W. Sanders, J. P. Moore, A. B. Ward & I. A. Wilson (2013) Crystal structure of soluble cleaved HIV-1 envelope trimer. Science epub ahead of print. PMID 24179159.

    3j5m: D. Lyumkis, J. P. Julien, N. de Val, A. Cupo, C. S. Potter, P. J. Klasse, D. R. Burton, R. W. Sanders, J. P. Moore, B. Carragher, I. A. Wilson & A. B. Ward (2013) Cryo-EM structure of fully glycosylated soluble cleaved HIV-1 envelope trimer. Science 342, 1484-1490.

    4cc8: A. Bartesaghi, A. Merk, M. J. Borgnia, J. L. S. Milne & S. Subramaniam (2013) Prefusion structure of trimeric HIV-1 envelope glycoprotein determined by cryo-electron microscopy. Nature Structural and Molecular Biology 20, 1352-1357.

    Source : pdb101.rcsb.org

    Bacteria, viruses, fungi and protist review

    Find and create gamified quizzes, lessons, presentations, and flashcards for students, employees, and everyone else. Get started for free!


    Bacteria, viruses, fungi and protis...

    Bacteria, viruses, fungi and protis... 54%


    Biology 6 years

    35 Qs

    1. Multiple-choice 30 seconds Q.

    A person who comes down with  malaria can infer that he or she contracted it from

    answer choices

    the bite of a tsetse fly

    contaminated water supply

    infections with Giardia

    the bite of an Anopheles mosquito

    2. Multiple-choice 30 seconds Q.

    Like animals, animal-like protists are

    answer choices autotrophs Heterotrophs unicellular prokaryotes 3. Multiple-choice 30 seconds Q.

    Which structure allow sarcodines such as amoebas to move?

    answer choices cilia contractile vacuole flagella pseudopods 4. Multiple-choice 30 seconds Q.

    What theory allowed for the first protist to evolve?

    answer choices endocymbiotic germ theory

    electrostatic theory

    cell theory 5. Multiple-choice 30 seconds Q.

    Which phylum causes the red tide t hat infects shelfish with a toxin?

    answer choices Bacillariophyta Chrysophyta Euglenophyta {yrrophyta 6. Multiple-choice 30 seconds Q.

    Viruses are exceptions to the cell theory, but they have some characteristics of living things. What is one of these characteristics

    answer choices

    They are made up of many specialized cells

    They contain genetic material

    They reproduce by mitosis

    They contain chlorophyll

    7. Multiple-choice 30 seconds Q.

    What characteristics of plants is shared by green algae?

    answer choices

    Photosynthetic pigments


    cell wall composition

    all of the above 8. Multiple-choice 30 seconds Q.

    An argument that does NOT support the classification of multi cellular green algae as  plants is that multicellular green algae

    answer choices

    display alteration of genertation

    contain chlorophyll a, which makes them green

    have highly specialized tissues

    live primarily in water

    9. Multiple-choice 30 seconds Q.

    Where are you likely to find a photoautotroph?

    answer choices

    in your refrigerator

    near the surfaces of lakes,streams and oceans

    in your digestive system

    in the darkness of the ocean

    10. Multiple-choice 30 seconds Q.

    Which of the following is algae's most important contribution to humans?

    answer choices

    as a photosynthesizer

    as a source for medicinal drugs

    as a source for industrial cemicals

    as a direct food source for humans

    11. Multiple-choice 30 seconds Q.

    In general algal blooms occur when

    answer choices

    the weather is stormy

    toxins accumulate ins hellfish

    nutrients decrease in water

    nutrients increase in water

    12. Multiple-choice 30 seconds Q.

    Which of the following is NOT a shared characteristic of protists?

    answer choices unicellular heterotroph prokaryote multicellular 13. Multiple-choice 30 seconds Q. Protozoans are answer choices

    animal-like autotrophs

    plantlike fungi

    fungus like protists

    animal -like protists

    14. Multiple-choice 30 seconds Q.

    Mushrooms are classified as

    answer choices common molds sac fungi club fungi imperfect fungi 15. Multiple-choice 30 seconds Q. Yeasts are known as answer choices club fungi imperfect fungi sac fungi 16. Multiple-choice 30 seconds Q.

    yeasts obtain energy by alcoholic fermentation in the absence of

    answer choices carbon dioxide sugar moisture oxygen 17. Multiple-choice 30 seconds Q.

    Which of the following statements about fungi is true?

    answer choices

    they deplete the soil of trace elements

    they do not affect trace elements

    they return trace elements to the soil

    they bind trace elements and hold them

    18. Multiple-choice 30 seconds Q.

    The thread like structures that make up the boides of multicellular fungi are called

    answer choices hyphae nuclei mold cell walls 19. Multiple-choice 30 seconds Q.

    What do fungi have in common with animals?

    answer choices they are autotrophs

    they are heterotrophs

    they have cell walls

    they use spores to reproduce

    20. Multiple-choice 30 seconds Q.

    Fungi that decompose dead organisms

    answer choices

    can cause serious disease in plants

    live in symbiosis with other organisms

    return important nutrients to the soil

    are often called pioneer organisms

    21. Multiple-choice 30 seconds Q.

    In prokaryotic organisms  DNA is found

    answer choices

    floating in the cytoplasm

    attached to ribosomes

    surrounded by nuclear  membrane

    contained in the vacuole

    22. Multiple-choice 30 seconds Q.

    Which cell structure does a bacterial cell lack?

    answer choices ribosome lysosome cell wall cytoplasm

    Source : quizizz.com


    The HIV-1 envelope (Env) glycoproteins play an essential role in the virus replication cycle by mediating the fusion between viral and cellular membranes during the entry process. The Env glycoproteins are synthesized as a polyprotein precursor, gp160, ...

    J Mol Biol. Author manuscript; available in PMC 2012 Jul 22.

    Published in final edited form as:

    J Mol Biol. 2011 Jul 22; 410(4): 582–608.

    doi: 10.1016/j.jmb.2011.04.042

    PMCID: PMC3139147

    NIHMSID: NIHMS294292

    PMID: 21762802

    HIV-1 Envelope Glycoprotein Biosynthesis, Trafficking, and Incorporation

    Mary Ann Checkley, Benjamin G. Luttge, and Eric O. Freed*

    Author information Copyright and License information Disclaimer

    The publisher's final edited version of this article is available at J Mol Biol

    See other articles in PMC that cite the published article.

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    The HIV-1 envelope (Env) glycoproteins play an essential role in the virus replication cycle by mediating the fusion between viral and cellular membranes during the entry process. The Env glycoproteins are synthesized as a polyprotein precursor, gp160, that is cleaved by cellular proteases to the mature surface glycoprotein gp120 and the transmembrane glycoprotein gp41. During virus assembly the gp120/gp41 complex is incorporated as heterotrimeric spikes into the lipid bilayer of nascent virions. These gp120/gp41 complexes then initiate the infection process by binding receptor and co-receptor on the surface of target cells. Much is currently known about the HIV-1 Env glycoprotein trafficking pathway and the structure of gp120 and the extracellular domain of gp41. However, the mechanism by which the Env glycoprotein complex is incorporated into virus particles remains incompletely understood. Genetic data support a major role for the cytoplasmic tail of gp41 and the matrix domain of Gag in Env glycoprotein incorporation. Still to be defined are the identities of host cell factors that may promote Env incorporation, and the role of specific membrane microdomains in this process. Here we review our current understanding of HIV-1 Env glycoprotein trafficking and incorporation into virions.

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    A. Overview of HIV-1 replication

    In vivo, human immunodeficiency virus type 1 (HIV-1) infects predominantly CD4+ T cells and cells of the monocyte/macrophage lineage. This cell tropism, which is intimately linked to the pathogenesis induced by HIV-1, is determined by the viral envelope (Env) glycoproteins. The Env glycoprotein complex projects from the virion surface as highly glycosylated spikes, composed of a heterotrimer of the surface (SU) glycoprotein gp120 and the transmembrane (TM) glycoprotein gp41. The entry process is initiated by the binding of gp120 to CD4, the primary attachment receptor for primate lentiviruses. CD4 binding triggers a conformational change in gp120 that enhances its affinity for a secondary receptor, or “coreceptor”. The major physiologically relevant coreceptors for HIV-1 are CCR5 and CXCR4. Upon binding of gp120 to the coreceptor, further conformational changes in both gp120 and gp41 trigger a membrane fusion reaction that delivers the viral core into the cytoplasm. HIV-1 can enter host cells through two different mechanisms, either direct, pH-independent fusion with the plasma membrane or clathrin-mediated endocytosis followed by low-pH fusion with the endosomal membrane.1,2,3

    The binding affinity between gp120 and CCR5 or CXCR4 to a large extent determines the cell tropism of a particular viral isolate. Macrophage-tropic HIV-1 isolates utilize CCR5 for entry and are thus designated as R5 viruses; these isolates can also infect primary CD4+ T cells but not T-cell lines. Viruses that primarily use CXCR4 are denoted X4-tropic; these strains can infect T-cell lines and primary T cells. R5X4 or “dual-tropic” strains can enter cells via either CCR5 and CXCR4.4 The CCR5 coreceptor is used during the primary or early, asymptomatic stage of HIV-1 infection and R5 viruses are largely responsible for person-to-person transmission.5 During the late stage of infection, viral isolates may arise that use CXCR4 for entry. The emergence in vivo of X4 or dual-tropic viruses is often associated with a sharp decline in the number of CD4+ T cells in infected individuals and the onset of AIDS-defining symptoms.

    Following entry into the cytosol, the viral RNA genome is converted (reverse transcribed) into double-stranded DNA by the viral enzyme reverse transcriptase (RT). The newly synthesized viral DNA is then translocated across the nuclear pore as part of a high-molecular-weight structure known as the preintegration complex.6,7,8,9,10 In the nucleus, the viral DNA is integrated into the host cell chromosomal DNA; this integration process is catalyzed by a second viral enzyme, integrase (IN). The integrated viral DNA directs the transcription of viral RNAs, which are transported into the cytoplasm where translation of the viral proteins takes place. The newly synthesized viral proteins, together with two single-stranded copies of full-length (unspliced) viral RNA, assemble into a new generation of viral particles. Concomitant with release of virus particles from the infected cell, a third viral enzyme, protease (PR), cleaves the Gag and GagPol polyprotein precursors, triggering the conversion of the immature particle to the mature virion. The virus replication cycle is now complete, and the mature virus particle can initiate a new cycle of infection. 11,12

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    B. Introduction to HIV-1 assembly

    The process of HIV-1 assembly is regulated by both viral and cellular factors. The Gag polyprotein precursor, Pr55Gag, is the major viral structural protein responsible for assembly; its expression is sufficient for the assembly, budding, and release of immature particles. Pr55Gag, usually simply referred to as Gag, is synthesized on cytosolic ribosomes and is composed of matrix (MA), capsid (CA), nucleocapsid (NC), and p6 domains, along with two spacer peptides (SP1 and SP2). Assembly of viral genomic RNA, the Env glycoprotein complex, and GagPol precursor protein (Pr160GagPol) into virus particles occurs in most cells at the plasma membrane (PM).12,13,14,15

    Source : www.ncbi.nlm.nih.gov

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