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Better understanding of uranyl-protein interactions is a prerequisite to predict uranium chemical toxicity in cells. The EF-hand motif of the calmodulin site I is about thousand times more affine for uranyl than for calcium, and threonine phosphorylation increases the uranyl affinity by two orders of magnitude at pH 7. In this study, we confront X-ray absorption spectroscopy with Fourier transform infrared (FTIR) spectroscopy, time-resolved laser-induced fluorescence spectroscopy (TRLFS), and structural models obtained by molecular dynamics simulations to analyze the uranyl coordination in the native and phosphorylated calmodulin site I. For the native site I, extended X-ray absorption fine structure (EXAFS) data evidence a short U−Oeq distance, in addition to distances compatible with mono- and bidentate coordination by carboxylate groups. Further analysis of uranyl speciation by TRLFS and thorough investigation of the fluorescence decay kinetics strongly support the presence of a hydroxide uranyl ligand. For a phosphorylated site I, the EXAFS and FTIR data support a monodentate uranyl coordination by the phosphoryl group and strong interaction with mono- and bidentate carboxylate ligands. This study confirms the important role of a phosphoryl ligand in the stability of uranyl-protein interactions. By evidencing a hydroxide uranyl ligand in calmodulin site I, this study also highlights the possible role of less studied ligands as water or hydroxide ions in the stability of protein-uranyl complexes. [ABSTRACT FROM AUTHOR]

Human Eg5, a mitotic motor of the kinesin superfamily, is involved in the formation and maintenance of the mitotic spindle. The recent discovery of small molecules that inhibit HsEg5 by binding to its catalytic motor domain leading to mitotic arrest has attracted more interest in Eg5 as a potential anticancer drug target. We have used hydrogen-deuterium exchange mass spectrometry and directed mutagenesis to identify the secondary structure elements that form the binding sites of new Eg5 inhibitors, in particular for S-trityl-L-cysteine, a potent inhibitor of Eg5 activity in vitro and in cell-based assays. The binding of this inhibitor modifies the deuterium incorporation rate of eight peptides that define two areas within the motor domain: Tyr125-Glu145 and Ile202-Leu227. Replacement of the Tyr125-Glu 145 region with the equivalent region in the Neurospora crassa conventional kinesin heavy chain prevents the inhibition of the Eg5 ATPase activity by S-trityl-L-cysteine. We show here that S-trityl-L-cysteine and monastrol both bind to the same region on Eg5 by induced fit in a pocket formed by helix α3-strand β5 and loop L5-helix α2, and both inhibitors trigger similar local conformational changes within the interaction site. It is likely that S-trityl-L-cysteine and monastrol inhibit HsEg5 by a similar mechanism. The common inhibitor binding region appears to represent a "hot spot" for HsEg5 that could be exploited for further inhibitor screening. [ABSTRACT FROM AUTHOR]

In MerT, the mercury transporter, a first cysteine pair, located in the first trans-membrane helix, receives mercury from the periplasm. Then, a second cysteine pair, housed in a cytoplasmic loop connecting the second and the third trans-membrane helices, is thought to transfer the metal to another cysteine pair located in the N-terminal extension of the mercuric reductase. We found that a 23-amino acid synthetic peptide corresponding to the cytoplasmic loop can bind one mercury atom per molecule and that this mercury atom can be transferred specifically to MerAa. The solution structure of Hg-bound ppMerT has been solved by 1H NMR spectroscopy. [Copyright &y& Elsevier]

Presents information on a study which derived a full-range amplitude spectrum for ocean surface waves. Nonfully developed sea spectrum; Scattering computations; Comparisons with other sea surface spectra; Conclusions.