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In brief

Lakes on Titan

The Cassini-Huygens spacecraft has discovered 75 lakes on the surface of Titan, Saturn's largest moon.1 The lakes, some of which span several tens of kilometers in diameter, are filled with liquid methane. The international team that presented these findings, which includes CNRS researchers, has thus shown that there is a methane cycle on Titan comparable to the water cycle on Earth.

1. E. R. Stofan et al., “The lakes of Titan,” Nature. 445: 61-4. 2007.

Contact: Philippe Paillou, philippe.paillou@obs.u-bordeaux1.fr

 

 

From its Ashes...

The retrovirus Phoenix, integrated in the human genome as a mobile element 5 million years ago, was reborn by the work of Thierry Heidmann and his colleagues.1 For the first time, they were able to generate viral particles, infectious for mammalian cells in culture, from a mobile element in the human genome. Although infectivity was very low, presumably because host cells have evolved mechanisms to resist uncontrolled virus propagation, this result indicates that human cells have kept the potential to produce infectious retroviruses.

1. M. Dewannieux et al., “Identification of an infectious progenitor for the multiple-copy HERV-K human endogenous retroelements,” Genome Res. 12:1548-56. 2006.

Contact: Thierry Heidmann, heidmann@igr.fr

 

 

Dangerous Fat

A surprising reservoir for Mycobacterium tuberculosis has been uncovered by Neyrolles and his coworkers: the adipose tissue.1 They detected M. Tuberculosis DNA in the fat tissue surrounding the kidneys, the stomach, the lymph nodes, the heart and the skin in about 30% of the 39 individuals tested, who died from causes other than TB. This could explain the ability of the tubercle bacillus to persist in its human host for exceptionally long periods of time, in a tissue where it escapes both anti-mycobacterial drugs and host defence mechanisms.

1. O. Neyrolles et al., “Is Adipose Tissue a Place for Mycobacterium tuberculosis Persistence?” PLoS ONE 1(1): e43. doi:10.1371/journal.pone.0000043. 2006.

Contact: Olivier Neyrolles, neyrolle@pasteur.fr

 

 

Leaded Toxicity

Why is lead toxic? Gourlaouen and Parisel1 from LCT2 suggest it could be due to a distortion of the molecule to which it binds. They took a close look at calmodulin, a calcium transporter that shows reduced efficiency after lead binding, and d-aminolevulinic acid dehydratase (d-ALAD), an enzyme whose activity is totally disrupted by lead binding. The team used model compounds to mimic lead binding and quantum computations to track structural changes wrought by the heavy metal. Their results indicate that the distortion induced by lead is well correlated to the extent of functional disruption and directly related to the positioning of a free pair of electrons in lead. The free pair of electrons seems to create a “shield” that completely disturbs the arrangement of atoms around lead in the bound molecule. This observation should help in the design of future lead-specific antidotes.

1. C. Gourlaouen and O. Parisel, “Is an electronic shield at the molecular origin of lead poisoning? A computational modeling experiment.” Angew. Chem. Int. Ed. 46: 553-556. 2007.

2. Laboratoire de chimie théorique (CNRS / Université Paris-VI joint lab).

Contact: Olivier Parisel, LCT, Ivry-sur-Seine  parisel@lct.jussieu.fr

 


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