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Isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP) represent the two central intermediates in the biosynthesis of isoprenoids. The recently discovered deoxyxylulose 5-phosphate pathway generates a mixture of IPP and DMAPP in its final step by reductive dehydroxylation of 1-hydroxy-2-methyl-2-butenyl 4-diphosphate. This conversion is catalyzed by IspH protein comprising a central iron-sulfur cluster as electron transfer cofactor in the active site. The five crystal structures of IspH in complex with substrate, converted substrate, products and [PP.sub.i] reported in this article provide unique insights into the mechanism of this enzyme. While IspH protein crystallizes with substrate bound to a [4Fe-4S] cluster, crystals of IspH in complex with IPP, DMAPP or inorganic pyrophosphate feature [3Fe-4S] clusters. The IspH:substrate complex reveals a hairpin conformation of the ligand with the C(1) hydroxyl group coordinated to the unique site in a [4Fe-4S] cluster of aconitase type. The resulting alkoxide complex is coupled to a hydrogen-bonding network, which serves as proton reservoir via a Thr167 proton relay. Prolonged x-ray irradiation leads to cleavage of the C(1)-O bond (initiated by reducing photo electrons). The data suggest a reaction mechanism involving a combination of Lewis-acid activation and proton coupled electron transfer. The resulting allyl radical intermediate can acquire a second electron via the iron-sulfur cluster. The reaction may be terminated by the transfer of a proton from the [beta]-phosphate of the substrate to C(1) (affording D MAPP) or C(3) (affording IPP). iron-sulfur protein | LytB protein | nonmevalonate pathway | terpene biosynthesis | isoprenoid biosynthesis doi/10.1073/pnas.0913045107

The synthesis and the spectroscopic and structural characterization of lower-rim-silylated and rare-earth-metalated calix[4]arenes are described. Depending on the steric bulk of their silyl groups, disilazane reagents HN(SiMe3)(sub 2) and HN(SiMe2)(sub 2) selectively yield bis- and tetrakis-silylated calix[4]arene derivatives and yttrium silylamide Y[N(SiHMe2)(sub 2)](sub 3)(THF)(sub 2) forms aryloxide bond-linked and silylated moieties on the lower-rim calix[4]arene surface

Discusses the presence of a symmetric lanthanidocene beta-diagnostic interaction. Delineation of origin and structure in terms of structural criteria, vibrational spectra, natural population analyses, natural bond orbitals and canonical molecular orbitals; Domination of the interaction by electrostatic effects.

Examines the feasibility of silylamide route for the synthesis of C2-symmetric metallocene complexes of the lanthanide elements. Isolation of indenyl-derived metallocene complexes; Access to a range of achiral through silylamine elimination reaction; Utilization of synthetic precursors to achieve exchange reactions with chelating molecules.

The haloarchaeon Halorubrum lacusprofundi is among the few polyextremophilic organisms capable of surviving in one of the most extreme aquatic environments on Earth, the Deep Lake of Antarctica (−18 °C to +11.5 °C and 21–28%, w/v salt content). Hence, H. lacusprofundi has been proposed as a model for biotechnology and astrobiology to investigate potential life beyond Earth. To understand the mechanisms that allow proteins to adapt to both salinity and cold, we structurally (including X-ray crystallography and molecular dynamics simulations) and functionally characterized the β-galactosidase from H. lacusprofundi (hla_bga). Recombinant hla_bga (produced in Haloferax volcanii) revealed exceptional stability, tolerating up to 4 M NaCl and up to 20% (v/v) of organic solvents. Despite being cold-adapted, hla_bga was also stable up to 60 °C. Structural analysis showed that hla_bga combined increased surface acidity (associated with halophily) with increased structural flexibility, fine-tuned on a residue level, for sustaining activity at low temperatures. The resulting blend enhanced structural flexibility at low temperatures but also limited protein movements at higher temperatures relative to mesophilic homologs. Collectively, these observations help in understanding the molecular basis of a dual psychrophilic and halophilic adaptation and suggest that such enzymes may be intrinsically stable and functional over an exceptionally large temperature range. [ABSTRACT FROM AUTHOR]