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Structural View of Biology


Biomolecular structures allow us to understand the molecular nature of healthy cells and treat the underlying molecular causes of disease. Our cells contain thousands of molecules that must all work in concert to keep us healthy. When any of these molecules fails, or when a poison or pathogenic organism attacks these molecules, it may cause disease. Our bodies have many defenses against disease, and medical science has developed powerful drugs to assist these defenses.

Viruses infect cells, hijacking them and forcing them to create many new copies of the virus. Structures of the components of viruses have allowed researchers to develop new vaccines and new drugs to fight infection by viruses such as influenza and HIV.

Scroll to a Molecule of the Month Feature in this subcategory:

  • Adenovirus

    Adenovirus

    Viruses are one of the most dangerous enemies to our health, attacking cells and causing deadly diseases like AIDS and influenza. However, scientists are currently discovering ways to trick viruses into improving our health instead of causing disease. Adenovirus is one of the viruses being used in this work. It is found around the world, but it usually causes only mild disease when it infects cells. It can be life-threatening, however, in infants or people with weakened immune systems. Modified forms of the virus are being developed to cure genetic diseases, to fight cancer, and to deliver vaccines.

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    Discussed Structures
    adenovirus
    adenovirus
    adenovirus
    adenovirus
  • Bacteriophage phiX174

    Bacteriophage phiX174

    The 10,000th entry in the Protein Data Bank, the bacteriophage phiX174, is a perfect example of how the science of protein structure has progressed in four decades. In 1960, the world got its first look at the structure of a protein. That first structure was the small protein myoglobin, composed of one protein chain and one heme group--about 1260 atoms in all. By contrast, the 10,000th entry in the PDB contains 420 protein chains and over half a million atoms. Enormous structures like this are not uncommon in the Protein Data Bank. The stakes have risen dramatically since the structure of myoglobin was first revealed.

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    Discussed Structures
    bacteriophage phiX174 procapsid
    bacteriophage phiX174 procapsid
  • Dengue Virus

    Dengue Virus

    Dengue virus is a major threat to health in tropical countries around the world. It is limited primarily to the tropics because it is transmitted by a tropical mosquito, but even with this limitation, 50-100 million people are infected each year. Most infected people experience dengue fever, with terrible headaches and fever and rashes that last a week or two. In some cases, however, the virus weakens the circulatory system and can lead to deadly hemorrhaging. Researchers are now actively studying the virus to try to develop drugs to cure infection, and vaccines to block infection before it starts.

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    Discussed Structures
    dengue virus capsid
    dengue virus capsid
    dengue virus envelope glycoprotein
    dengue virus envelope glycoprotein
    dengue virus methyltransferase
    dengue virus methyltransferase
    dengue virus methyltransferase
    dengue virus methyltransferase
    dengue virus protease/helicase
    dengue virus protease/helicase
  • HIV Capsid

    HIV Capsid

    Viruses come in many shapes and sizes, ranging from simple protein shells filled with RNA or DNA to membrane-enveloped particles that rival cells in complexity. HIV is one of these complex viruses, surrounded by a membrane and filled with a diverse collection of viral and cellular molecules. The genome of HIV, which is composed of two strands of RNA, is packaged inside a distinctive cone-shaped capsid, which protects the RNA and delivers it to the cells that HIV infects.

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    Discussed Structures
    HIV capsid and antibody Fab
    HIV capsid and antibody Fab
    HIV capsid hexamer
    HIV capsid hexamer
    HIV capsid pentamer
    HIV capsid pentamer
  • HIV Envelope Glycoprotein

    HIV Envelope Glycoprotein

    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.

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    Discussed Structures
    HIV Envelope Glycoprotein
    HIV Envelope Glycoprotein
    HIV Envelope Glycoprotein
    HIV Envelope Glycoprotein
    SIV Envelope Glycoprotein
    SIV Envelope Glycoprotein
  • HIV-1 Protease

    HIV-1 Protease

    Drugs that attack HIV-1 protease are one of the triumphs of modern medicine. The AIDS epidemic started a few short decades ago-- before that, HIV was unknown. These drugs demonstrate the powerful tools that medical science has to combat a new disease. Already, researchers have discovered a panel of effective drugs which slow the growth of the virus to a standstill. Important problems still remain, however. In particular, an effective vaccine against HIV is not available. But today, HIV-infected individuals have potent options for treatment.

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    Discussed Structures
    HIV protease with a peptide-like inhibitor
    HIV protease with a peptide-like inhibitor
    HIV protease with saquinavir
    HIV protease with saquinavir
  • Hemagglutinin

    Hemagglutinin

    Influenza virus is a dangerous enemy. Normally, the immune system fights off infections, eradicating the viruses and causing a few days of miserable flu symptoms. Yearly flu vaccines prime our immune system, making it ready to fight the most common strains of influenza virus. But once every couple of decades, a new strain of influenza appears that is far more pathogenic, allowing it to spread rapidly. This happened at the end of World War I, and the resultant pandemic killed over 20 million people, more than twice the number of people that were killed in the war.

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    Discussed Structures
    hemagglutinin
    hemagglutinin
    hemagglutinin
    hemagglutinin
    hemagglutinin and antibodies
    hemagglutinin and antibodies
  • Influenza Neuraminidase

    Influenza Neuraminidase

    Influenza virus is continually changing and every decade or so, a dangerous new strain appears and poses a threat to public health. This year, there has been an outbreak of a new strain of H1N1 flu, more commonly known as swine flu. The H1N1 designation refers to the two molecules that cover the surface of the virus: hemagglutinin and neuraminidase. Together, these two molecules control the infectivity of the virus. Hemagglutinin plays the starring role as the virus approaches a cell, binding to polysaccharide chains on the cell surface and then injecting the viral genome into the cell. Neuraminidase, on the other hand, plays its major role after the virus leaves an infected cell. It ensures that the virus doesn't get stuck on the cell surface by clipping off the ends of these polysaccharide chains.

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    Discussed Structures
    neuraminidase
    neuraminidase
    neuraminidase and sialic acid
    neuraminidase and sialic acid
    neuraminidase and antibodies
    neuraminidase and antibodies
  • Integrase

    Integrase

    Retroviruses, such as HIV, are particularly insidious. Most viruses infect a cell, force it make many new copies of the virus, and then leave when the cell is used up. Retroviruses, however, take a long-term approach to infection. They enter cells and build a DNA copy of their genome.

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    Discussed Structures
    integrase target capture complex
    integrase target capture complex
    integrase strand transfer complex
    integrase strand transfer complex
  • Parvoviruses

    Parvoviruses

    Viruses are finely tuned to perform their deadly job. Many viruses are highly specific: they infect only a particular animal or plant, and may even only infect a few types of cells within their preferred hosts. However, viruses occasionally cross the line, and gain the ability to infect other hosts. This is often termed viral emergence, and has been sensationalized as a major threat to global health in books such as The Hot Zone. Fortunately, this type of switching occurs only rarely, but when it does, it can be a disaster.

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    Discussed Structures
    feline panleukopenia virus (FPV)
    feline panleukopenia virus (FPV)
    canine parvovirus
    canine parvovirus
    B19 parvovirus
    B19 parvovirus
  • Poliovirus and Rhinovirus

    Poliovirus and Rhinovirus

    Viruses are biological hijackers. They attack a living cell and force it to make many new viruses, often destroying the cell in the process. Picornaviruses, or "little RNA viruses," are among the most simple viruses. They are composed of a modular protein shell, which seeks out and binds to a target cell surface, surrounding a short piece of RNA, which contains all of the information needed to co-opt the cell's machinery and direct the construction of new viruses. In spite of their simplicity, or perhaps because of it, the picornaviruses are also among the most important viruses for human health and welfare. Three familiar examples are shown here: poliovirus at the top (PDB entry 2plv), rhinovirus at the center (PDB entry 4rhv), and the virus that causes foot and mouth disease in livestock at the bottom (PDB entry 1bbt).

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    Discussed Structures
    poliovirus capsid
    poliovirus capsid
    rhinovirus capsid
    rhinovirus capsid
    foot-and-mouth disease virus capsid
    foot-and-mouth disease virus capsid
    rhinovirus bound to its cellular receptor
    rhinovirus bound to its cellular receptor
  • Reverse Transcriptase

    Reverse Transcriptase

    Viruses are tricky. They use all sorts of unusual mechanisms during their attacks on cells. HIV is no exception. It is a retrovirus, which means that it has the ability to insert its genetic material into the genome of the cells that it infects. But, infectious HIV particles carry their genome in RNA strands. Somehow, during infection, the virus needs to make a DNA copy of its RNA genome. This is very unusual, because all of the normal cellular machinery is designed to make RNA copies from DNA, but not the reverse. DNA is normally only created using other DNA strands as a template. This tricky reversal of synthesis is performed by the enzyme reverse transcriptase, shown here from PDB entry 3hvt. Inside its large, claw-shaped active site, it copies the HIV RNA and creates a double-stranded DNA version of the viral genome. This then integrates into the cell's DNA, and later instructs the cell to make additional copies of the virus.

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    Discussed Structures
    reverse transcriptase with DNA
    reverse transcriptase with DNA
    reverse transcriptase with nevirapine
    reverse transcriptase with nevirapine
  • Simian Virus 40

    Simian Virus 40

    Simian virus 40 is an example of how simple a virus can be and still perform its deadly job. Viruses are tiny machines with a single purpose: to reproduce themselves. They enter cells and hijack their synthetic machinery, forcing them to create new viruses. SV40 does this with very little molecular machinery. It is enclosed by a spherical capsid composed of 360 copies of one protein, seen in PDB entry 1sva, and a few copies of two others. This capsid is just big enough to enclose a small circle of DNA 5243 nucleotides long, which contains the barest minimum of information needed to get into the cell and make new viruses.

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    Discussed Structures
    SV40 capsid
    SV40 capsid
    SV40 T-antigen
    SV40 T-antigen
    SV40 T-antigen
    SV40 T-antigen
    SV40 T-antigen
    SV40 T-antigen
  • Tobacco Mosaic Virus

    Tobacco Mosaic Virus

    Tobacco mosaic virus (TMV) has been at the center of virus research since its discovery over a hundred years ago. TMV was the first virus to be discovered. Late in the 19th century, researchers found that a tiny infectious agent, too small to be a bacterium, was the cause of a disease of tobacco plants. It then took 30 years of work before the nature of this mysterious agent became apparent. In a Nobel-prize-winning study, Wendell Stanley coaxed the virus to form crystals, and discovered that it was composed primarily of protein. Others quickly discovered that there was also RNA in the virus. Then, many prominent structural researchers (including J. D. Bernal, Rosalind Franklin, Ken Holmes, Aaron Klug, Don Caspar, and Gerald Stubbs) used X-ray diffraction and electron microscopy to probe the structure of the virus.

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    Discussed Structures
    tobacco mosaic virus
    tobacco mosaic virus
    tobacco mosaic virus disk
    tobacco mosaic virus disk

Please see our usage polices for citation and reprint information. Copies of the illustrations used in these features are available for download as high resolution TIFF images. Please note that the structures used to illustrate each installment are chosen at the discretion of the authors; the features are not intended to represent a historical record. The process behind the creation of this feature is described by the author.