Chemical Education Today
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Nature: Gifts from Mother Earth—The Good, the Bad, and the Ugly by Sabine Heinhorst and Gordon C. Cannon
plays a role in insect flight, helps fleas jump, and cicadas chirp (Figures 2 and 3). The amino acid sequence of resilins contains repeated short sequence motifs that are thought to endow the protein with its elastic properties. Elvin and colleagues from several Australian universities and CSIRO institutes produced large amounts of this “elastic” portion of fruit fly resilin in the bacterium Escherichia coli (2005, 437, October 13, 999– 1002; see also the News and Views feature, 2005, 437, October 13, 961). They purified the recombinant truncated protein
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photo: Frank Filippi, CSIRO.
Figure 2. Photomontage of a dragonfly on a knotted resilin rod. The dityrosine linkages cause the material to fluoresce blue under UV illumination. Artwork courtesy David Merritt, David McLenaghan, Nancy Liyou, and Ted Hagemeijer.
photo: Darren Wong and David Merritt.
The Good If your New Year’s resolution was to avoid fast food joints and from now on feast on fresh, healthful salads with olive oil-based dressings instead, you may be doing yourself an even greater favor than you thought. A possible chemical basis for the purported health benefits of olive oil, a prominent ingredient in Mediterranean diets, has been uncovered by Beau-champ and colleagues from Monell Chemical Senses Center, University of the Sciences in Philadelphia, University of Philadelphia, and from Firmenich in Princeton, NJ (2005, 437, September 1, 45). Cold-pressed extra-virgin olive oil contains (᎑)deacetoxy-ligstroside aglycone, or oleocanthal, which works as a non-steroidal anti-inflammatory agent, targeting the same two cyclooxygenase enzymes in the prostaglandin biosynthesis pathway that are also affected by the common pain killer ibuprofen (see Figure 1). Prostaglandins, hormone-like derivatives of the C-20 multiunsaturated fatty acid arachidonic acid, mediate the inflammatory response and a variety of other effects (see http:// m i c ro. m a g n e t . f s u . e d u / m i c ro / g a l l e r y / p ro s t a g l a n d i n / prostaglandin.html; accessed Dec 2005). Both oleocanthal enantiomers, “natural” or synthetic, are equally active in inhibiting their target enzymes and, as suggested by the authors of this communication, may be the ingredient in olive oil that, like ibuprofen and aspirin, can help to lower one’s risk of heart attack, stroke, and even cancer (for more information on risks and benefits of overthe-counter non-steroidal anti-inflammatory medicines, see http://search.cancer.org/search?client=amcancer&site= amcancer&output=xml_no_dtd&proxystylesheet= a m c a n c e r & r e s t r i c t = c a n c e r & q = ov e r - t h e - c o u n t e r + nonsteroidal+anti-inflammatory+medicines; and http:// www.americanheart.org/presenter.jhtml?identifier=4456; both sites accessed Dec 2005). How could fruit flies, fleas, and other flying insects possibly be considered a good gift from Mother Earth? They produce the protein resilin, which is a natural elastomer that
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Figure 1. Structures of ibuprofen (top) and (᎑)oleocanthal (bottom). Structures by D. J. Rosado.
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Figure 3. Image showing the fluorescent (due to dityrosine) resilin pad in the legs of the flea. This pad is squeezed as the leg muscles operate; all of the energy imparted via the leg muscles is released from the resilin pad in about one millisecond. This is how fleas manage to achieve their remarkable jumping feats.
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Chemical Education Today
The Bad Rice is an important cereal crop that serves as staple food for a large portion of the human population (for information on global food crops, see http://www.fao.org/documents/ show_cdr.asp?url_file=/docrep/U8480E/U8480E07.htm; for a lesson plan on rice as a global crop, see http://www.askasia.org/ frclasrm/lessplan/l000008.htm; both sites accessed Dec 2005). A “bad” fungus of the genus Rhizopus causes considerable crop losses through the disease known as rice seedling blight. The polyketide rhizoxin (Figure 4) released by Rhizopus wreaks havoc with the roots of the rice plants by inhibiting cell division; the fungus then feasts on the resulting decaying plant material. Work by Partida-Martinez and Hertweck from the Leibniz Institute for Natural Products Research and Infection Biology in Jena, Germany (2005, 437, October 6, 884– 888; see also the News and Views feature, 2005, 437, October 6, 823–824) has now established that Rhizopus has a partner in crime. The researchers showed that rhizoxin-producing Rhizobium strains carry bacteria of the genus Burgholderia as intracellular (endo-) symbionts. Furthermore, the gene for the polyketide synthase enzyme that catalyzes a step in toxin biosynthesis is present only in the DNA of the bacteria and not in the genetic material of the fungus. The authors were able to confirm the role of Burgholderia in toxin production by isolating bacteria from the pathogenic fungus and establishing a pure culture. Even living by itself without its fungal host, Burgholderia produces rhizoxin and, upon establishment of an endosymbiotic relationship, is able to convert a nontoxin producing Rhizopus strain to one that releases rhizoxin. As the authors point out, several symbiotic associations between animals and bacteria also produce natural products of interest and warrant a closer look at the role played by each symbiont in their biosynthesis. For the Rhizopus–Burgholderia symbiosis, an understanding of the pathway leading to the synthesis of rhiz-oxin will have important implications for an effective management of this rice pathogen and, since rhizoxin appears to slow the growth of some human cancers, may lead to novel drug development strategies. … and the Ugly With the possible exception of some entomologists, most readers will agree that ticks are not particularly handsome and warrant being placed in the “ugly” category of gifts from Mother Earth. In addition to lacking in the beauty department, the deer tick Ixodes scapularis (Figure 5) often carries as a nasty little cargo, Borrelia burgdorferi, the spirochete bacteria that cause Lyme disease (for information about Lyme disease see http://www.cdc.gov/ncidod/dvbid/lyme/; accessed Dec 2005). Researchers from Yale University School of Medicine, www.JCE.DivCHED.org
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Figure 4. Structure of rhizoxin. Structure by D. J. Rosado.
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The University of Texas Southwestern Medical Center, University of North Carolina at Charlotte, Connecticut Agricultural Experimental Station, and from L2 Diagnostics showed how these bacteria use a tick protein to their own advantage (Ramamoorthi and colleagues, 2005, 436, July 28, 573–577). Through an as-yet-unknown mechanism, B. burgdorferi induces its arthropod host to specifically increase production of the salivary gland protein Salp15, which is known to inhibit the immune response of the tick’s mammalian prey. The Salp15 protein interacts with OspC, an outer surface lipoprotein of B. burdorferi that facilitates movement of the bacteria from the tick’s gut to its salivary gland when the insect feeds on a mammal. Comparison of the number of viable spirochetes remaining in mice following injection with Salp15-coated wild-type or mutant bacteria unable to produce OspC clearly established the critical role the tick protein plays in helping B. burgdorferi to colonize even those mice that had previously developed resistance to infection by the spirochetes. As a final coup de grace, the researchers specifically knocked out Salp15 production in the tick with an RNA interference approach (see our column in this Journal, 2004, 81, 1404–1405 for information on RNA interference) and showed that mice that had been fed on by the Sap15-deficient ticks had drastically reduced B. burgdorferi levels. Knowledge of the molecular players that bring about an effective infection of the mammalian host by B. burgdorferi may point to novel therapeutic approaches and to the development of a better vaccine for Lyme disease. Sabine Heinhorst and Gordon C. Cannon are in the Department of Chemistry and Biochemistry, University of Southern Mississippi, Hattiesburg, MS 39406-5043; email: sabine.
[email protected] and
[email protected]. photo: Michigan Lyme Disease Assn.
in soluble form and crosslinked individual polypeptide chains through their tyrosine side chains to generate an amorphous hydrogel. Analysis of the material’s elastomeric properties by atomic force microscopy revealed almost perfect resilience that is superior to that of two synthetic rubbers. The authors suggest future applications for this remarkable biopolymer-derived material in the biomedical field or in other industries that depend on highly resilient elastic polymers.
Figure 5. Ixodes scapularis, the deer tick. Shown from left to right are larval stage, nymph stage, a mature male, and a mature female animal.
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