A VLBI experiment using a remote atomic clock via a coherent fibre link.

We describe a VLBI experiment in which, for the first time, the clock reference is delivered from a National Metrology Institute to a radio telescope using a coherent fibre link 550 km long. The experiment consisted of a 24-hours long geodetic campaign, performed by a network of European telescopes; in one of those (Medicina, Italy) the local clock was alternated with a signal generated from an optical comb slaved to a fibre-disseminated optical signal. The quality of the results obtained with this facility and with the local clock is similar: interferometric fringes were detected throughout the whole 24-hours period and it was possible to obtain a solution whose residuals are comparable to those obtained with the local clock.

The crystal structure of C176A mutated [Fe]-hydrogenase suggests an acyl-iron ligation in the active site iron complex.

[Fe]-hydrogenase is one of three types of enzymes known to activate H(2). Crystal structure analysis recently revealed that its active site iron is ligated square-pyramidally by Cys176-sulfur, two CO, an "unknown" ligand and the sp(2)-hybridized nitrogen of a unique iron-guanylylpyridinol-cofactor. We report here on the structure of the C176A mutated enzyme crystallized in the presence of dithiothreitol (DTT).

The crystal structure of [Fe]-hydrogenase reveals the geometry of the active site.

Biological formation and consumption of molecular hydrogen (H2) are catalyzed by hydrogenases, of which three phylogenetically unrelated types are known: [NiFe]-hydrogenases, [FeFe]-hydrogenases, and [Fe]-hydrogenase. We present a crystal structure of [Fe]-hydrogenase at 1.75 angstrom resolution, showing a mononuclear iron coordinated by the sulfur of cysteine 176, two carbon monoxide (CO) molecules, and the sp2-hybridized nitrogen of a 2-pyridinol compound with back-bonding properties similar to those of cyanide.

Structural organization of essential iron-sulfur clusters in the evolutionarily highly conserved ATP-binding cassette protein ABCE1.

The ABC protein ABCE1, formerly named RNase L inhibitor RLI1, is one of the most conserved proteins in evolution and is expressed in all organisms except eubacteria. Because of its fundamental role in translation initiation and/or ribosome biosynthesis, ABCE1 is essential for life. Its molecular mechanism has, however, not been elucidated.