11 research outputs found
Carbonyl Reduction by YmfI Completes the Modification of EF-P in \u3cem\u3eBacillus subtilis\u3c/em\u3e to Prevent Accumulation of an Inhibitory Modification State
Translation elongation factor P (EFâP) in Bacillus subtilis is required for a form of surface migration called swarming motility. Furthermore, B. subtilis EFâP is postâtranslationally modified with a 5âaminopentanol group but the pathway necessary for the synthesis and ligation of the modification is unknown. Here we determine that the protein YmfI catalyzes the reduction of EFâPâ5 aminopentanone to EFâPâ5 aminopentanol. In the absence of YmfI, accumulation of 5âaminopentanonated EFâP is inhibitory to swarming motility. Suppressor mutations that enhanced swarming in the absence of YmfI were found at two positions on EFâP, including one that changed the conserved modification site (Lys 32) and abolished postâtranslational modification. Thus, while modification of EFâP is thought to be essential for EFâP activity, here we show that in some cases it can be dispensable. YmfI is the first protein identified in the pathway leading to EFâP modification in B. subtilis, and B. subtilis encodes the first EFâP ortholog that retains function in the absence of modification
EF-P Post-Translational Modification Has Variable Impact on Polyproline Translation in \u3cem\u3eBacillus subtilis\u3c/em\u3e
Elongation factor P (EF-P) is a ubiquitous translation factor that facilitates translation of polyproline motifs. In order to perform this function, EF-P generally requires posttranslational modification (PTM) on a conserved residue. Although the position of the modification is highly conserved, the structure can vary widely between organisms. In Bacillus subtilis, EF-P is modified at Lys32 with a 5-aminopentanol moiety. Here, we use a forward genetic screen to identify genes involved in 5-aminopentanolylation. Tandem mass spectrometry analysis of the PTM mutant strains indicated that ynbB, gsaB, and ymfI are required for modification and that yaaO, yfkA, and ywlG influence the level of modification. Structural analyses also showed that EF-P can retain unique intermediate modifications, suggesting that 5-aminopentanol is likely directly assembled on EF-P through a novel modification pathway. Phenotypic characterization of these PTM mutants showed that each mutant does not strictly phenocopy the efp mutant, as has previously been observed in other organisms. Rather, each mutant displays phenotypic characteristics consistent with those of either the efp mutant or wild-type B. subtilis depending on the growth condition. In vivo polyproline reporter data indicate that the observed phenotypic differences result from variation in both the severity of polyproline translation defects and altered EF-P context dependence in each mutant. Together, these findings establish a new EF-P PTM pathway and also highlight a unique relationship between EF-P modification and polyproline context dependence
Silicon quantum dots in photovoltaic devices: device fabrication, characterization and comparison of materials
The realization of crystalline silicon tandem solar cells relies on silicon nanocrystal (Si NC) quantum dots as
the absorber of the top solar cell. Quantum confinement of charge carriers within the nanocrystals permits to
achieve a band gap up to 2 eV which can be adjusted according to the size of the nanocrystals. This enables the
construction of all-crystalline Si tandem solar cells, and increases the theoretical efficiency limit from 33 % to
42.5 % due to the addition of a second band gap. In this work, the electrical and photovoltaic properties of Si
NC films are assessed and the most prominent material systems (SiO2, Si3N4, SiC) are compared. P-i-n solar
cells are presented which feature Si NC as the intrinsic absorber layer and permit to characterize quantum
confinement electrically on device level. P-i-n solar cells with Si NC in SiC in the i-region have yielded open
circuit voltages of up to 370mV
Cyclic Rhamnosylated Elongation Factor P Establishes Antibiotic Resistance in \u3cem\u3ePseudomonas aeruginosa\u3c/em\u3e
Elongation factor P (EF-P) is a ubiquitous bacterial protein that is required for the synthesis of poly-proline motifs during translation. In Escherichia coli and Salmonella enterica, the posttranslational β-lysylation of Lys34 by the PoxA protein is critical for EF-P activity. PoxA is absent from many bacterial species such as Pseudomonas aeruginosa, prompting a search for alternative EF-P posttranslation modification pathways. Structural analyses of P. aeruginosa EF-P revealed the attachment of a single cyclic rhamnose moiety to an Arg residue at a position equivalent to that at which β-Lys is attached to E. coli EF-P. Analysis of the genomes of organisms that both lack poxA and encode an Arg32-containing EF-P revealed a highly conserved glycosyltransferase (EarP) encoded at a position adjacent to efp. EF-P proteins isolated from P. aeruginosa ÎearP, or from a ÎrmlC::acc1 strain deficient in dTDP-l-rhamnose biosynthesis, were unmodified. In vitro assays confirmed the ability of EarP to use dTDP-l-rhamnose as a substrate for the posttranslational glycosylation of EF-P. The role of rhamnosylated EF-P in translational control was investigated in P. aeruginosa using a Pro4-green fluorescent protein (Pro4GFP) in vivo reporter assay, and the fluorescence was significantly reduced in Îefp, ÎearP, and ÎrmlC::acc1 strains. ÎrmlC::acc1, ÎearP, and Îefp strains also displayed significant increases in their sensitivities to a range of antibiotics, including ertapenem, polymyxin B, cefotaxim, and piperacillin. Taken together, our findings indicate that posttranslational rhamnosylation of EF-P plays a key role in P. aeruginosa gene expression and survival
Electrical Properties of Recrystallised SiC Films from PECVD Precursors for Silicon Quantum Dot Solar Cell Applications
Silicon carbide (SiC) is a promising host material for silicon quantum dots (Si QDs), which are being investigated as absorber materials for tandem solar cells based solely on crystalline silicon. Amorphous silicon carbide (a-SiC) films are deposited by plasma-enhanced chemical vapour deposition (PECVD) and annealed under the same conditions usually used to precipitate Si QDs. During annealing, the films shrink by 20%, and some a-SiC transforms into SiC nanocrystals (nc-SiC) about 3 nm in size. P-type doping with boron is found to inhibit SiC crystallisation and lower conductance as compared to intrinsic films. N-type doping with phosphorus on the other hand promotes SiC crystallisation and leads to a higher conductance. The trends in conductance are ascribed solely to the effect of the dopant on crystallisation. Al, Ti, Cr, Ni20%Cr, and ITO are all found to form Ohmic contacts to the SiC films on deposition, with no change in contact properties brought about by sintering at 425°C. Temperature-dependent conductivity measurements on intrinsic SiC films reveal two distinct activation energies; 65 meV below 200 K, and 158 meV above 200 K
Carbonyl reduction by YmfI in Bacillus subtilis
Translation elongation factor P (EFâP) in Bacillus subtilis is required for a form of surface migration called swarming motility. Furthermore, B. subtilis EFâP is postâtranslationally modified with a 5âaminopentanol group but the pathway necessary for the synthesis and ligation of the modification is unknown. Here we determine that the protein YmfI catalyzes the reduction of EFâPâ5 aminopentanone to EFâPâ5 aminopentanol. In the absence of YmfI, accumulation of 5âaminopentanonated EFâP is inhibitory to swarming motility. Suppressor mutations that enhanced swarming in the absence of YmfI were found at two positions on EFâP, including one that changed the conserved modification site (Lys 32) and abolished postâtranslational modification. Thus, while modification of EFâP is thought to be essential for EFâP activity, here we show that in some cases it can be dispensable. YmfI is the first protein identified in the pathway leading to EFâP modification in B. subtilis, and B. subtilis encodes the first EFâP ortholog that retains function in the absence of modification
EF-P Posttranslational Modification Has Variable Impact on Polyproline Translation in Bacillus subtilis
Elongation factor P (EF-P) is a ubiquitous translation factor that facilitates translation of polyproline motifs. In order to perform this function, EF-P generally requires posttranslational modification (PTM) on a conserved residue. Although the position of the modification is highly conserved, the structure can vary widely between organisms. In Bacillus subtilis, EF-P is modified at Lys32 with a 5-aminopentanol moiety. Here, we use a forward genetic screen to identify genes involved in 5-aminopentanolylation. Tandem mass spectrometry analysis of the PTM mutant strains indicated that ynbB, gsaB, and ymfI are required for modification and that yaaO, yfkA, and ywlG influence the level of modification. Structural analyses also showed that EF-P can retain unique intermediate modifications, suggesting that 5-aminopentanol is likely directly assembled on EF-P through a novel modification pathway. Phenotypic characterization of these PTM mutants showed that each mutant does not strictly phenocopy the efp mutant, as has previously been observed in other organisms. Rather, each mutant displays phenotypic characteristics consistent with those of either the efp mutant or wild-type B. subtilis depending on the growth condition. In vivo polyproline reporter data indicate that the observed phenotypic differences result from variation in both the severity of polyproline translation defects and altered EF-P context dependence in each mutant. Together, these findings establish a new EF-P PTM pathway and also highlight a unique relationship between EF-P modification and polyproline context dependence
Cyclic Rhamnosylated Elongation Factor P Establishes Antibiotic Resistance in Pseudomonas aeruginosa
Elongation factor P (EF-P) is a ubiquitous bacterial protein that is required for the synthesis of poly-proline motifs during translation. In Escherichia coli and Salmonella enterica, the posttranslational β-lysylation of Lys34 by the PoxA protein is critical for EF-P activity. PoxA is absent from many bacterial species such as Pseudomonas aeruginosa, prompting a search for alternative EF-P posttranslation modification pathways. Structural analyses of P. aeruginosa EF-P revealed the attachment of a single cyclic rhamnose moiety to an Arg residue at a position equivalent to that at which β-Lys is attached to E. coli EF-P. Analysis of the genomes of organisms that both lack poxA and encode an Arg32-containing EF-P revealed a highly conserved glycosyltransferase (EarP) encoded at a position adjacent to efp. EF-P proteins isolated from P. aeruginosa ÎearP, or from a ÎrmlC::acc1 strain deficient in dTDP-l-rhamnose biosynthesis, were unmodified. In vitro assays confirmed the ability of EarP to use dTDP-l-rhamnose as a substrate for the posttranslational glycosylation of EF-P. The role of rhamnosylated EF-P in translational control was investigated in P. aeruginosa using a Pro(4)-green fluorescent protein (Pro(4)GFP) in vivo reporter assay, and the fluorescence was significantly reduced in Îefp, ÎearP, and ÎrmlC::acc1 strains. ÎrmlC::acc1, ÎearP, and Îefp strains also displayed significant increases in their sensitivities to a range of antibiotics, including ertapenem, polymyxin B, cefotaxim, and piperacillin. Taken together, our findings indicate that posttranslational rhamnosylation of EF-P plays a key role in P. aeruginosa gene expression and survival
Silicon quantum dots in photovoltaic devices: device fabrication, characterization and comparison of materials
The realization of crystalline silicon tandem solar cells relies on silicon nanocrystal (Si NC) quantum dots as
the absorber of the top solar cell. Quantum confinement of charge carriers within the nanocrystals permits to
achieve a band gap up to 2 eV which can be adjusted according to the size of the nanocrystals. This enables the
construction of all-crystalline Si tandem solar cells, and increases the theoretical efficiency limit from 33 % to
42.5 % due to the addition of a second band gap. In this work, the electrical and photovoltaic properties of Si
NC films are assessed and the most prominent material systems (SiO2, Si3N4, SiC) are compared. P-i-n solar
cells are presented which feature Si NC as the intrinsic absorber layer and permit to characterize quantum
confinement electrically on device level. P-i-n solar cells with Si NC in SiC in the i-region have yielded open
circuit voltages of up to 370mV