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Science Concentrates Landing Page

December 13, 2004 | A version of this story appeared in Volume 82, Issue 50

New drug target for pneumonia bacterium

Scientists studying how Streptococcus pneumoniae regulates the production of isoprenoids have identified a promising new strategy for designing antibiotics to combat this pneumonia-causing bacterium. S. pneumoniae kills more than 3,700 people each day worldwide, and "the threat of multiple-antibiotic-resistant strains of this organism has never been greater," says Thomas S. Leyh of Albert Einstein College of Medicine. Leyh notes that S. pneumoniae makes the isoprenoids it needs to survive from isopentenyl diphosphate, the end product of the mevalonate pathway: Mevalonate is doubly phosphorylated to produce diphosphomevalonate (shown), which is then decarboxylated to yield isopentenyl diphosphate. Upon closer examination of this pathway, Leyh found that diphosphomevalonate potently inhibits the enzyme that carries out the initial phosphorylation of mevalonate by binding to an allosteric site distinct from the enzyme's active site [Biochemistry, published online Dec. 4,]. The human version of this enzyme is not inhibited by diphosphomevalonate, indicating that the allosteric site is a promising target for the design of new antimicrobials, he says.

Zygote's H2O2 burst elucidated

After one lucky sperm fertilizes one highly sought after egg, the new zygote quickly puts up a protective barrier to keep out other sperm suitors. Plus, a rapid burst of hydrogen peroxide along the membrane's edge catalyzes cross-linking, making the shield impenetrable. For years, how toxic H2O2 gets there has been a puzzle. Now, a group at Brown University, headed by biologist Gary M. Wessel, has identified the responsible dual oxidase enzyme in sea urchin eggs [Dev. Cell, 7, 801 (2004)]. The transmembrane protein has two distinct functional domains. A reductase portion at one end converts oxygen to H2O2, while at the other end, a peroxidase domain likely breaks down the H2O2 to water and oxygen. The researchers hypothesize that having such opposing activities in the same protein is practical. The enzyme both produces the H2O2 that hardens the barrier and promptly neutralizes the toxic molecule so it cannot harm the zygote. Whether mammalian eggs use such a dual oxidase counterpart at fertilization isn't yet known.

Protopolymer in unbonded netherworld

At low temperatures, the units of a polymer can be coaxed into lining up and interacting while still remaining unbonded. This 'protopolymer,' consisting of phenylene chains on a crystalline copper surface, not only represents a new chemical state but could be a tool for doing molecular assembly, report Paul S. Weiss and Gregory S. McCarty at Pennsylvania State University [J. Am. Chem. Soc., published online Dec. 2,]. Scientists have seen prebonding behavior in pairs of molecules on metal surfaces, but never before in long ordered chains. The copper surface acts as an extended catalytic site, bringing together and aligning the phenylene units. Weiss and McCarty were able to pull individual molecules off the chain, which indicated that the units were not covalently bound.

Noninvasive detection of breast cancer

A noninvasive imaging technique that could ease diagnosis of breast cancer by eliminating the need for mammograms or confirmatory biopsies has been developed by Eric Wickstrom of Thomas Jefferson University, Philadelphia, and coworkers [J. Nucl. Med., 45, 2070 (2004)]. Currently, an invasive and often painful biopsy must be performed to determine whether a lump found by mammography is cancerous, and many early tumors are not detected by mammography. In an effort to solve both problems, Wickstrom and colleagues synthesized a probe (shown) with three parts: a peptide (green) that localizes to breast cancer tissue (by binding insulin-like growth factor 1 receptor, which is expressed in large amounts there); a peptide nucleic acid sequence (orange) that binds mRNA for cyclin D1 (which is also overexpressed in breast cancer); and a gamma-emitting technetium-chelating peptide that can be detected scintigraphically. By administering the conjugate to mice with human breast cancer grafts, the researchers were able to successfully detect cancerous tissue externally. The Jefferson scientists hope to soon test the strategy on women volunteers.

Cold fusion review mixed, inconclusive

Fifteen years ago, a Department of Energy panel examined the controversial claims of "cold fusion" researchers and concluded that they did not stand up to scientific scrutiny. Now, at the behest of a band of cold fusion advocates, an 18-member panel assembled by DOE has taken a fresh look at the latest research in the field and has come to a similar conclusion, although the panel was split. The 18 panelists, whose expertise is in nuclear physics, materials science, electrochemistry, and other relevant fields, have not been identified. They were asked to evaluate evidence that nuclear reactions such as deuterium-deuterium fusion can occur in deuterium-loaded metals at low energies--for example, in an electrochemical cell with a palladium electrode. Cold fusion researchers have dreamed of harnessing these purported reactions to produce clean, abundant energy. Although some panelists found the evidence for low-energy nuclear reactions at least somewhat convincing, most did not believe the evidence was conclusive. But, the reviewers nearly unanimously agreed that funding agencies should entertain peer-reviewed proposals for experiments to address specific questions in this field. The report is available at<br > News_Releases/DOE-SC/2004/low_energy.


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