Structures of furanosides : geometrical analysis of low-temperature X-ray and neutron crystal structures of five crystalline methyl pentofuranosides

Crystal structures of all five crystalline methyl D-pentofuranosides, methyl alpha -D-arabinofuranoside (1), methyl beta -D-arabinofuranoside (2), methyl alpha -D-lyxofuranoside (3), methyl beta -D-ribofuranoside (4) and methyl alpha -D-xylofuranoside (5) have been determined by means of cryogenic X-ray and neutron crystallography. The neutron diffraction experiments provide accurate. unbiased H-atom positions which are especially important because of the critical role of hydrogen bonding in these systems. This paper summarizes the geometrical and conformational parameters of the structures of all five crystalline methyl pentofuranosides, several of them reported here for the first time. The methyl pentofuranoside structures are compared with the structures of the five crystalline methyl hexopyranosides for which accurate X-ray and neutron structures have been determined. Unlike the methyl hexopyranosides, which crystallize exclusively in the C-1 chair conformation, the five crystalline methyl pentofuranosides represent a very wide range of ring conformations

Three aromatic residues are required for electron transfer during iron mineralization in Bacterioferritin

Ferritins are iron storage proteins that overcome problems of toxicity and poor bioavailability of iron by catalysing iron oxidation and mineralization through the activity of a diiron ferroxidase site. Unlike in other ferritins, the oxidized di-Fe3+ site of Escherichia coli bacterioferritin (EcBFR) is stable and therefore does not function as a conduit for the transfer of Fe3+ into the storage cavity, but instead acts as a true catalytic cofactor that cycles its oxidation state while driving Fe2+ oxidation in the cavity. Here we demonstrate that EcBFR mineralization depends on three near-diiron site aromatic residues, Tyr25, Tyr58 and Trp133, and that a transient radical is formed on Tyr25. The data indicate that the aromatic residues, together with a previously identified inner surface iron site, promote mineralization by ensuring the simultaneous delivery of two electrons, derived from Fe2+ oxidation in the BFR cavity, to the di-ferric catalytic site for safe reduction of O2

Characterization of single crystals of the large ribosomal particles from a mutant of Bacillus stearothermophilus

Single, three-dimensional crystals of 50S ribosomal subunits, from a mutant of Bacillus stearothermophilus that lacks the protein L11, have been characterized using a synchrotron X-ray source. The crystals of the mutated particles grow under the same conditions and are isomorphous to those of the wild type of the same bacteria. They are orthorhombic, contain at least one 2-fold screw axis, and have unit cell dimensions of a = 350(±10) A ̊, b = 670(± 10) A ̊, and c = 910(±10) A ̊. They diffract to 15 to 18 A ̊ resolution at 4 °C and are stable in the synchrotron beam for several hours

Single crystals of large ribosomal particles from Halobacterium marismortui diffract to 6 Å

Large, well-ordered three-dimensional crystals of 50 S ribosomal subunits from Halobacterium marismortui have been obtained by seeding. The crystals have been characterized with synchrotron X-ray radiation as monoclinic, space group P21, with unit cell dimensions of a = 182(+-5)A, b = 584(+-10)A, c = 186(+-5)A, Beta = 109. At 4 °C, the crystals (0.6 mm × 0.6 mm × 0.1 mm) diffract to 6 Å resolution and are stable in the synchrotron beam for several hours. Compact packing is reflected from the crystallographic unit cell parameters and from electron micrographs of positively stained thin sections of embedded crystal

Single crystals of large ribosomal particles from Halobacterium marismortui diffract to 6 Å

Large, well-ordered three-dimensional crystals of 50 S ribosomal subunits from Halobacterium marismortui have been obtained by seeding. The crystals have been characterized with synchrotron X-ray radiation as monoclinic, space group P21, with unit cell dimensions of a = 182(+-5)A, b = 584(+-10)A, c = 186(+-5)A, Beta = 109. At 4 °C, the crystals (0.6 mm × 0.6 mm × 0.1 mm) diffract to 6 Å resolution and are stable in the synchrotron beam for several hours. Compact packing is reflected from the crystallographic unit cell parameters and from electron micrographs of positively stained thin sections of embedded crystal