ppGpp analogues inhibit synthetase activity of Rel proteins from Gram-negative and Gram-positive bacteria.

A prominent feature of the stringent response is the accumulation of two unusual phosphorylated derivatives of GTP and GDP (pppGpp: 5'-triphosphate-3'-diphosphate, and ppGpp: 5'-3'-bis-diphosphate), collectively called (p)ppGpp, within a few seconds after the onset of amino-acid starvation. The synthesis of these 'alarmone' compounds is catalyzed by RelA homologues. Other features of the stringent response include inhibition of stable RNA synthesis and modulation of transcription, replication, and translation. (p)ppGpp accumulation is important for virulence induction, differentiation and antibiotic resistance. We have synthesized a group of (p)ppGpp analogues and tested them as competitive inhibitors of Rel proteins in vitro. 2'-Deoxyguanosine-3'-5'-di(methylene bisphosphonate) [compound (10)] was found as an inhibitor that reduces ppGpp formation in both Gram-negative and Gram-positive bacteria. In silico docking together with competitive inhibition analysis suggests that compound (10) inhibits activity of Rel proteins by competing with GTP/GDP for its binding site. As Rel proteins are completely absent in mammalians, this appears to be a very attractive approach for the development of novel antibacterial agents.

From dusk till dawn: one-plasmid systems for light-regulated gene expression.

Signaling photoreceptors mediate diverse organismal adaptations in response to light. As light-gated protein switches, signaling photoreceptors provide the basis for optogenetics, a term that refers to the control of organismal physiology and behavior by light. We establish as novel optogenetic tools the plasmids pDusk and pDawn, which employ blue-light photoreceptors to confer light-repressed or light-induced gene expression in Escherichia coli with up to 460-fold induction upon illumination. Key features of these systems are low background activity, high dynamic range, spatial control on the 20-µm scale, independence from exogenous factors, and ease of use. In optogenetic experiments, pDusk and pDawn can be used to specifically perturb individual nodes of signaling networks and interrogate their role. On the preparative scale, pDawn can induce by light the production of recombinant proteins and thus represents a cost-effective and readily automated alternative to conventional induction systems.

It depends on the hinge: a structure-functional analysis of galectin-8, a tandem-repeat type lectin.

Galectin-8, a member of the galectin family of mammalian lectins, is made of two carbohydrate-recognition domains (CRDs), joined by a "hinge" region. Ligation of integrins by galectin-8 induces a distinct cytoskeletal organization, associated with activation of the extracellular-regulated kinase (ERK) and phosphatidylinositol 3-kinase signaling cascades. We show that these properties of galectin-8 are mediated by the concerted action of its two CRDs and involve both protein-sugar and protein-protein interactions. Accordingly, the isolated N- or C-CRD domains of galectin-8 or galectin-8 mutated at selected residues implicated in sugar binding (E251Q; W85Y, W248Y, W[85,248]Y) exhibited reduced sugar binding, which was accompanied by severe impairment in the capacity of these mutants to promote the adhesive, spreading, and signaling functions of galectin-8. Other mutations that did not impair sugar binding (e.g. E88Q) still impeded the signaling and cell-adherence functions of galectin-8. Deletion of the "hinge" region similarly impaired the biological effects of galectin-8. These results provide evidence that cooperative interactions between the two CRDs and the "hinge" domain are required for the proper functioning of galectin-8.