Chemical and enzymatic synthesis of fluorinated-dehydroalanine-containing peptides

Michael acceptors have long been recognized as reactive functionalities that may link a biologically active molecule to its cellular target. 1,2-Dehydro amino acids are potential Michael acceptors present in a large number of natural products, but their reactivity is modulated by the deactivating nature of the alpha-amino group engaged in an amide bond. We describe here the preparation of 3-fluoro-1,2-dehydroalanine moieties within peptides that significantly enhance the reactivity of the Michael acceptor. Two different routes were designed to access these compounds, one relying on chemical means to introduce the desired functionality and the second taking advantage of a peptide epimerase. In the chemical approach, the fluoro-Pummerer reaction of cysteine derivatives afforded 3-fluorocysteine residues that were oxidized to the corresponding sulfoxides, followed by thermolytic elimination to provide the desired 3-fluorodehydroalanines. The mechanism of the fluoro-Pummerer reaction was investigated and several possible pathways were ruled out. The enzymatic approach utilized the dipeptide epimerase YcjG from Escherichia coli. Difluorinated alanine was incorporated at the C terminus of a dipeptide by chemical means. The resulting peptide proved to be a substrate for YcjG, which catalyzed fluoride elimination to provide the 3-fluorodehydroalanine-containing peptide. Mechanistic investigations showed that fluoride elimination occurred faster than epimerization and at a rate close to that of epimerization of Ala-Ala.     

The impact of the customer order decoupling point on type and level of supply chain integration

Literature suggests that more supply chain (SC) integration increases of SC performance. However, recent research shows that contextual factors affect the effectiveness of SC integration efforts. Specifically, the location of the customer order decoupling point (CODP) might be such a factor, but there is limited empirical evidence. This study explores the impact of the location of the CODP on SC integration. It empirically investigates upstream, internal and downstream SC integration efforts in twelve metal parts producing Dutch companies to offer a comprehensive view of the effects of the location of the CODP on SC integration. Our results show a clear relationship between SC integration and the location of the CODP. Specifically, make-to-order (MTO), assemble-to-order (ATO) and make-to-stock (MTS) companies show relatively high levels in upstream, internal and downstream SC integration, respectively. Moreover, MTO companies mainly share forecast information and engage in joint R&D with their suppliers, ATO companies focus on internal SC integration using information systems and planning, while MTS companies interact with their customers intensively to exchange forecast information. Our study adds to the insight on the application of SC integration in different situations and offers initial evidence for the effects of the location of the CODP on SC integration.     

Salience is only briefly represented: Evidence from probe-detection performance.

Salient objects in the visual field tend to capture attention. The present study aimed to examine the time-course of salience effects using a probe-detection task. Eight experiments investigated how the salience of different orientation singletons affected probe reaction time as a function of stimulus onset asynchrony (SOA) between the presentation of a singleton display and a probe display. The results demonstrate that salience consistently affected probe reaction time at the shortest SOA. The effect of salience disappeared as SOA increased. These results suggest that contrary to the assumption of major theories on visual selection, salience is transiently represented in our visual system allowing the effects of salience on attentional selection to be only short-lived. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Characterization of a Dehydratase and Methyltransferase in the Biosynthesis of Ribosomally Synthesized and Post-translationally Modified Peptides in Lachnospiraceae

As a result of the exponential increase in genomic data, discovery of novel ribosomally synthesized and post-translationally modified peptide natural products (RiPPs) has progressed rapidly in the past decade. The lanthipeptides are a major subset of RiPPs. Through genome mining we identified a novel lanthipeptide biosynthetic gene cluster (lah) from Lachnospiraceae bacterium C6A11, an anaerobic bacterium that is a member of the human microbiota and which is implicated in the development of host disease states such as type 2 diabetes and resistance to Clostridium difficile colonization. The lah cluster encodes at least seven putative precursor peptides and multiple post-translational modification (PTM) enzymes. Two unusual class II lanthipeptide synthetases LahM1/M2 and a substrate-tolerant S-adenosyl-l -methionine (SAM)-dependent methyltransferase LahS_B are biochemically characterized in this study. We also present the crystal structure of LahS_B in complex with product S-adenosylhomocysteine. This study sets the stage for further exploration of the final products of the lah pathway as well as their potential physiological functions in human/animal gut microbiota.     

The Role of Stimulus-Driven and Goal-Driven Control in Saccadic Visual Selection.

Four experiments were conducted to investigate the role of stimulus-driven and goal-driven control in saccadic eye movements. Participants were required to make a speeded saccade toward a predefined target presented concurrently with multiple nontargets and possibly 1 distractor. Target and distractor were either equally salient (Experiments 1 and 2) or not (Experiments 3 and 4). The results uniformly demonstrated that fast eye movements were completely stimulus driven, whereas slower eye movements were goal driven. These results are in line with neither a bottom-up account nor a top-down notion of visual selection. Instead, they indicate that visual selection is the outcome of 2 independent processes, one stimulus driven and the other goal driven, operating in different time windows. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Modelling of silicon condenser microphones

Several models concerning the sensitivity of capacitive pressure sensors have been presented in the past. Modelling of condenser microphones, which can be considered to be a special type of capacitive pressure sensor, usually requires a more complicated analysis of the sensitivity, because they have a strong electric field in the air gap. It is found that the mechanical sensitivity of condenser microphones with a circular diaphragm, either with a large initial tension or without any initial tension, increases with increasing bias voltage (and the corresponding static deflection), whereas the mechanical sensitivity of other capacitive pressure sensors does not depend on the static deflection. It is also found that the mechanical sensitivity increases with increasing input capacitance of a preamplifier. In addition, the open-circuit electrical sensitivity and, consequently, the total sensitivity too, also increases with increasing bias voltage (or static deflection). However, the maximum allowable sound pressure at which the diaphragm collapses, an effect that has to be taken into account, decreases with increasing static deflection in most cases, ulthnately resulting in an optimum value for the bias voltage. The model for microphones with a circular highly tensioned diaphragm has been verified successfully for two microphone types.