Chemical communication in proteobacteria: Biochemical and structural studies of signal synthases and receptors required for intercellular signalling

Cell-cell communication via the production and detection of chemical signal molecules has been the focus of a great deal of research over the past decade. One class of chemical signals widely used by proteobacteria consists of N-acyl-homoserine lactones, which are synthesized by proteins related to LuxI of Vibrio fischeri and are detected by proteins related to the V. fischeri LuxR protein. A related marine bacterium, Vibrio harveyi, communicates using two chemical signals, one of which, autoinducer-2 (AI-2), is a furanone borate diester that is synthesized by the LuxS protein and detected by a periplasmic protein called LuxP. Evidence from a number of laboratories suggests that AI-2 may be used as a signal by diverse groups of bacteria, and might permit intergeneric signalling. These two families of signalling systems have been studied from the perspectives of physiology, ecology, biochemistry, and more recently, structural biology. Here, we review the biochemistry and structural biology of both acyl-homoserine-lactone-dependent and AI-2-dependent signalling systems

Electronic transport for a crossed graphene nanoribbon junction with and without doping

The electronic transport property for a crossed junction of graphene nanoribbons with and without impurity doping is investigated numerically by a fully self-consistent non-equilibrium Green’s function method combined with density functional theory. It is demonstrated that the transport property of the junction depends sensitively on both the dopant positions and the geometry of junction. Specifically, the I-V characteristics of the junction with either nitrogen- or boron-doped stems always show metallic behavior. However, the current strongly depends on the doping atomic species and sites, but slightly depends on the geometry of junction under small bias voltage. The findings here may be important in the design of graphene-based electronic devices for realizing on/off states. Copyright EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg 2010