Structure of influenza virus

influenza-virion3In this week’s discussion of swine flu A/Mexico/09 (H1N1), we have considered many aspects of influenza virus biology that might not be familiar to some readers of virology blog. I thought it might be useful to explain how the virus multiplies, how it infects us, and how we combat infection. Today we’ll start with the basic structure of influenza virus, illustrated above.

The influenza virion (as the infectious particle is called) is roughly spherical. It is an enveloped virus – that is, the outer layer is a lipid membrane which is taken from the host cell in which the virus multiplies. Inserted into the lipid membrane are ‘spikes’, which are proteins – actually glycoproteins, because they consist of protein linked to sugars – known as HA (hemagglutinin) and NA (neuraminidase). These are the proteins that determine the subtype of influenza virus (A/H1N1, for example). We’ll discuss later how the HA and NA are given subtype numbers. The HA and NA are important in the immune response against the virus; antibodies (proteins made by us to combat infection) against these spikes may protect against infection. The NA protein is the target of the antiviral drugs Relenza and Tamiflu. Also embedded in the lipid membrane is the M2 protein, which is the target of the antiviral adamantanes – amantadine and rimantadine.

Beneath the lipid membrane is a viral protein called M1, or matrix protein. This protein, which forms a shell, gives strength and rigidity to the lipid envelope. Within the interior of the virion are the viral RNAs – 8 of them for influenza A viruses. These are the genetic material of the virus; they code for one or two proteins. Each RNA segment, as they are called, consists of RNA joined with several proteins shown in the diagram: B1, PB2, PA, NP. These RNA segments are the genes of influenza virus. The interior of the virion also contains another protein called NEP.

This week, when we discussed the nucleotide sequence of swine influenza RNAs, we were referring to these RNA molecules. Tomorrow I’ll show you how each RNA codes for protein. This way it will be easier to understand the meaning of the swine flu virus sequences that were released this week.

Let me know if this type of explanation is useful, and if you would like me to continue.

118 thoughts on “Structure of influenza virus”

  1. Carlos Enriquez

    Influenza virus types are determined by the nucleoprotein rather than the H or N.

    Bull World Health Organ. 1971; 45(1): 119–124.

  2. i bought a blood zapper. and read dr becks work for nasa. take vitaminc tablets 1000mg before using a blood zapper. electroporation occurs magnifying the vit c to like 60,ooomg like some armies combi pens. never fear a virus again.

  3. NEP, or nuclear export protein, is involved in the export of the viral
    RNA-protein complex from the nucleus, where the viral RNA is
    replicated, to the cytoplasm.

  4. you say this
    “because they consist of protein linked to sugars – known as HA (hemagglutinin) and NA (neuraminidase). These are the proteins that determine the type of influenza virus (A, B, or C) and”
    but HA and NA do not determine the type of influenza virus but only the subtype. NP and M determine the type of influenza virus A, B or C

  5. Influenza types were originally (years ago) defined by
    cross-reactivity, using antisera, against the core proteins, M1 and
    NP. By sequence comparison of HA and NA it would be possible today to
    determine whether an influenza virus is type A or B or C. I’ve made a
    few corrections to the post to reflect this information.

  6. Thank you for useful information!
    I think you should correct ‘diagram: B1, PB2 …’–> to ‘diagram: PB1, PB2’ in the following sentence .
    “Each RNA segment, as they are called, consists of RNA joined with several proteins shown in the diagram: B1, PB2, PA, NP”

  7. improve your sentences’ and grammer, and get your sentences stright and to the point, and the structure of the cell is wrong, firstly the reason scientists couldn’ t find an cure so fast was because once the cell came into contact with anti-bodies the cell use them to it’s adventage -gasp

  8. Feastingwithbears

    You are rather uninformative and not helpful. The rest of you giving scientific answers and comments are about as helpful as a toddler in the trenches, that is to say I would use you as a human shield (I do not condone family violence however, this is merely an example of my feelings towards you). The majority of people viewing this article want a basic run through on the life processes of the virus, not a lecture on the structure of viruses in our world. I am doing a school project and was thoroughly disappointed with the amount of confusing (to some) scientific comments, the only productive comment was “poopy” sums up this article pretty well I think.

    Kind Regards, your life advisor.

  9. there should be better deffentions for some of the more scientific words here, explaining how they work in the body

  10. Really helpful, it’s so hard to find an explanation of this at the right level for what I need!

  11. All those who are posting complaints about either the grammatical quality of this text or the scientific detail, go somewhere else if it is too advanced for you.  This is written by a professor who knows lots about this subject.  You are wasting his time.  Thank you Vincent Racaniello this article is very helpful.

  12. To all those haters, if you don’t like it, you don’t need to start whining. This article is helpful and if you didn’t like it, go sook in a corner.

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  14. This article is very useful and provides information in a very simple & understandable manner. Those who criticized it are lame people.

  15. HELLO Professor
    thanks for your guidance
    i have a question you have a powerpoint file about H1N1?
    i think if you make a ppt and upload it,it will be better

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  17. Enjoyed both the graphic and the biochemical outline. Would also be fun to see an SEM produced picture of the virus. How has digital imaging changed things?

  18. I really like how you made this simple and clear.  I would enjoy reading more similar posts.  Thanks very much.

  19. A quite naive question that you will be able to answer I hope.

    Historically, A and B viruses were distinguished through assays based on antigenicity. Same thing for the different subtypes of Influenza A. Among one subtype of A, it is also antigenicity that permits to distinguish between different drifted strains.
    Phylogenetic trees, based on amino acid sequence of HA, permit also to distinguish the different strains, subtypes, A/B viruses.
    However, is there a threshold that permits to determine the level of difference?
    Do we have to admit that former researchers were quite lucky to use antibodies permitting first to distinguish between H1 and H3 for example and not antibodies discriminating drifted strains?
    Why are B viruses divided into Yamagata and Victoria and not HxNx and HyNy ? How can we say that there is only one HA and one NA type for B, there are not enough antigenic differences among glycoproteins from V and Y strains?
    Thanks in advance to clarify these points !

  20. I am a student of biochemistry and molecular biology.I have fallen in a trouble to understand the structure of influenza virus..nd it really helped  me to know about the concept:)Thank u sir.

  21. spain n barca footy fan

    thanks for the useful information. you’ve helped me alot in my science project. 🙂

  22. Good day Professor,
    my name is Jenny and i have
    question: What is you advice or statement to
    prevent pandemics such as swine flu to
    spread through public transport?


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  24. i’d just really like to say how much i appreciate the whole “less is more” style of writing i see here. it really makes things concise and clear while still giving very detailed information. thanks a ton.

  25. The “alive or dead” debate isn’t conclusive in either direction, but it has has its own RNA, a membrane, and behavior. So for all intents and purposes, it’s alive, and please, learn to spell if you’re going to comment on a scientific forum…

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