Most small molecules are unable to rapidly traverse the outer membrane of Gram-negative bacteria and accumulate inside these cells, making the discovery of much-needed drugs for these pathogens very challenging. Current understanding of the physicochemical properties that dictate small-molecule accumulation in Gram-negatives is largely based on retrospective analyses of antibacterials that suggest polarity and molecular weight as key factors. Here we assess the ability of over 180 diverse compounds to accumulate in Escherichia coli. Computational analysis of the results reveals major differences from the retrospective studies, namely that the small molecules that are most likely to accumulate contain an amine, are amphiphilic and rigid, and have low globularity. These guidelines were then applied to convert deoxynybomycin, a natural product that is active only against Gram-positive organisms, into an antibiotic with activity against a diverse panel of multi-drug-resistant Gram-negative pathogens. We anticipate these findings will aid in the discovery and development of antibiotics effective against Gram-negative bacteria.

Multilayer silicene, the silicon analogue of multilayer graphene, grown on silver (111) surfaces, possesses a honeycomb (ͱ3 Â ͱ3)R30 reconstruction, observed by scanning tunnelling microscopy at room temperature, past the initial formation of the dominant, 3Â3 reconstructed, silicene monolayer. For a few layers silicene film we measure by synchrotron radiation photoelectron spectroscopy, a cone-like dispersion at the Brillouin zone centre due to band folding. p* and p states meet at $0.25 eV below the Fermi level, providing clear evidence of the presence of gapless Dirac fermions. V

SummaryProtein ADP-ribosylation is a highly dynamic post-translational modification. The rapid turnover is achieved, among others, by ADP-(ribosyl)hydrolases (ARHs), an ancient family of enzymes that reverses this modification. Recently ARHs came into focus due to their role as regulators of cellular stresses and tumor suppressors. Here we present a comprehensive structural analysis of the enzymatically active family members ARH1 and ARH3. These two enzymes have very distinct substrate requirements. Our data show that binding of the adenosine ribose moiety is highly diverged between the two enzymes, whereas the active sites harboring the distal ribose closely resemble each other. Despite this apparent similarity, we elucidate the structural basis for the selective inhibition of ARH3 by the ADP-ribose analogues ADP-HPD and arginine-ADP-ribose. Together, our biochemical and structural work provides important insights into the mode of enzyme-ligand interaction, helps to understand differences in their catalytic behavior, and provides useful tools for targeted drug design.

We have purified a protein that binds phosphatidylinositol 3,4,5-trisphosphate [PtdIns(3,4,5)P3] using beads bearing a PtdIns(3,4,5)P3 analogue. This protein, with a molecular mass of 43 kDa, was termed PtdIns(3,4,5)P3-binding protein. The partial amino acid sequences were determined and a full-length cDNA encoding the protein was isolated from bovine brain cDNA library. The clone harbored an open reading frame of 373 amino acids which contained one zinc finger motif similar to that of ADP-ribosylation-factor GTPase-activating protein and two pleckstrin homology domains. The entire sequence was 83 % similar to centaurin a, another PtdIns(3,4,5)P3-binding protein. The protein bound PtdIns(3,4,5)P3 with a higher affinity than it did inositol 1,3,4,5-tetrakisphosphate, phosphatidylinositol 4,5-bisphosphate, phosphatidylinositol 3,4-bisphosphate, and phosphatidylinositol 3-phosphate suggesting that the binding to PtdIns(3,4,5)P3 was specific. The binding activity was weaker in the mutants with a point mutation in the conserved sequences in each pleckstrin homology domain. Introduction of both mutations abolished the activity. These results suggest that this new binding protein hinds PtdIns(3,4,5)P3 through two pleckstrin domains present in the molecule.Keywords: phosphatidylinositol 3,4,5-trisphosphate; inositolphospholipid 3-kinase; signal transduction.