The structure of glucose dehydrogenase from the extreme halophile Haloferax mediterranei has been solved at 1.6-Å resolution under crystallization conditions which closely mimic the ''in vivo'' intracellular environment. The decoration of the enzyme's surface with acidic residues is only partially neutralized by bound potassium counterions, which also appear to play a role in substrate binding. The surface shows the expected reduction in hydrophobic character, surprisingly not from changes associated with the loss of exposed hydrophobic residues but rather arising from a loss of lysines consistent with the genome wide-reduction of this residue in extreme halophiles. The structure reveals a highly ordered, multilayered solvation shell that can be seen to be organized into one dominant network covering much of the exposed surface accessible area to an extent not seen in almost any other protein structure solved. This finding is consistent with the requirement of the enzyme to form a protective shell in a dehydrating environment.Archaea ͉ x-ray structure ͉ water structure ͉ hydrophobic surface ͉ surface lysines

The structure of BPSL1549, a protein of unknown function from Burkholderia pseudomallei, reveals a similarity to Escherichia coli cytotoxic necrotizing factor 1. We found that BPSL1549 acted as a potent cytotoxin against eukaryotic cells and was lethal when administered to mice. Expression levels of bpsl1549 correlate with conditions expected to promote or suppress pathogenicity. BPSL1549 promotes deamidation of glutamine-339 of the translation initiation factor eIF4A, abolishing its helicase activity and inhibiting translation. We propose to name BPSL1549 Burkholderia lethal factor 1.

D-glutamate is an essential building block of the peptidoglycan layer in bacterial cell walls and can be synthesized from L-glutamate by glutamate racemase (RacE). The structure of a complex of B. subtilis RacE with D-glutamate reveals that the glutamate is buried in a deep pocket, whose formation at the interface of the enzyme's two domains involves a large-scale conformational rearrangement. These domains are related by pseudo-2-fold symmetry, which superimposes the two catalytic cysteine residues, which are located at equivalent positions on either side of the alpha carbon of the substrate. The structural similarity of these two domains suggests that the racemase activity of RacE arose as a result of gene duplication. The structure of the complex is dramatically different from that proposed previously and provides new insights into the RacE mechanism and an explanation for the potency of a family of RacE inhibitors, which have been developed as novel antibiotics.

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Analysis of the crystal structures of the free enzyme and of the binary complexes with NAD(+) and glycerol show that the active site of GlyDH lies in the cleft between the enzyme's two domains, with the catalytic zinc ion playing a role in stabilizing an alkoxide intermediate. In addition, the specificity of this enzyme for a range of diols can be understood, as both hydroxyls of the glycerol form ligands to the enzyme-bound Zn(2+) ion at the active site. The structure further reveals a previously unsuspected similarity to dehydroquinate synthase, an enzyme whose more complex chemistry shares a common chemical step with that catalyzed by glycerol dehydrogenase, providing a striking example of divergent evolution. Finally, the structure suggests that the NAD(+) binding domain of GlyDH may be related to that of the classical Rossmann fold by switching the sequence order of the two mononucleotide binding folds that make up this domain.