Friday, November 30, 2007

The vaults resolved

What are vaults? These 50 nm-long hollow capsules are made of almost 100 proteins, plus RNA components, and rank among the largest supramolecular structures found in eukaryotic cells. Yet their function is still unknown. They could have a function in the immune system, in tumour drug resistance, or in nucleus-cytoplasm trafficking. There is also a practical reason for studying vaults. This kind of molecular spaceship could one day be engineered to carry pharmacological agents in the cells.

Characterize molecular complexes as gigantic as vaults is one of the most daunting tasks for science today. They lie in a "dark" length scale. Smaller molecules are easy often to crystallize and thus to get their structure solved atomically thanks to X ray diffraction. Larger structures can be characterized with microscopy. Vaults lie in the middle: too large to efficiently crystallize, too small to be solved with conventional microscopy. The three-dimensional general barrel shape of vaults has been structurally described by mean of cryo-TEM at low resolution. A hollow symmetric shell (able to encapsulate entire ribosomes), with two protrudring caps, was revealed, but that pretty was it.

Now, Daniel H. Anderson and others have resolved the structure of the vault shell protein at 0.9 nm resolution. The picture is still fuzzy compared to the atomic resolution of many protein crystal structures, but it is an enormous step forward compared to the previous structures. The vault can now be understood in terms of the assemby of the individual molecules that compose it. It is a beautiful, daunting mosaic of intertwined protein chains.

You can read the full paper on PLoS Biology.

Friday, November 2, 2007

An hydrogen eclipse

How do you catch a planet around another star? One of the most important techniques used is looking for transits -that is, the tiny dip in star brightness when a planet passes in front of the star itself. By studying such phenomena, a surprising number of informations can be squeezed out, for example on the remote planet atmosphere composition or temperature. Recently, researchers at the UCSC discovered something really odd about the gas giant HD 209458 b. They compared the transit depth (i.e. the amount of starlight blocked by the planet) in visible light and in the ultraviolet band that is absorbed by hydrogen -the Lyman-alpha line.

They did find that the transit is much deeper in the Lyman-alpha light, just like if the planet was much larger in that frequence (see image above). This means that HD 20958 b has a gigantic hydrogen comet-like cloud around it, that would be quite transparent for our sight but dramatically conspicuous in the ultraviolet.

Read the original story on the Systemic blog.