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Carbonylation is currently used as a marker for irreversible protein oxidative damage. Several studies indicate that carbonylated proteins are more prone to degradation than their nonoxidized counterparts. In this study, we observed that in Escherichia coli, more than 95% of the total carbonyl content consisted of insoluble protein and most were cytosolic proteins. We thereby demonstrate that, in vivo, carbonylated proteins are detectable mainly in an aggregate state. Finally, we show that detectable carbonylated proteins are not degraded in vivo. Here we propose that some carbonylated proteins escape degradation in vivo by forming carbonylated protein aggregates and thus becoming nondegradable. In light of these findings, we provide evidence that the accumulation of nondegradable carbonylated protein presented in an aggregate state contributes to the increases in carbonyl content observed during senescence.

Abstract Background Due to its capacity to produce large amounts of cellulases, Trichoderma reesei is increasingly been researched in various fields of white biotechnology, especially in biofuel production from lignocellulosic biomass. The commercial enzyme mixtures produced at industrial scales are not well characterized, and their proteinaceous components are poorly identified and quantified. The development of proteomic methods has made it possible to comprehensively overview the enzymes involved in lignocellulosic biomass degradation which are secreted under various environmental conditions. Results The protein composition of the secretome produced by industrial T. reesei (strain CL847) grown on a medium promoting the production of both cellulases and hemicellulases was explored using two-dimensional electrophoresis and MALDI-TOF or LC-MS/MS protein identification. A total of 22 protein species were identified. As expected, most of them are potentially involved in biomass degradation. The 2D map obtained was then used to compare the secretomes produced by CL847 and another efficient cellulolytic T. reesei strain, Rut-C30, the reference cellulase-overproducing strain using lactose as carbon source and inducer of cellulases. Conclusion This study provides the most complete mapping of the proteins secreted by T. reesei to date. We report on the first use of proteomics to compare secretome composition between two cellulase-overproducing strains Rut-C30 and CL847 grown under similar conditions. Comparison of protein patterns in both strains highlighted many unexpected differences between cellulase cocktails. The results demonstrate that 2D electrophoresis is a promising tool for studying cellulase production profiles, whether for industrial characterization of an entire secretome or for a more fundamental study on cellulase expression at genome-wide scale.

The genome of the facultative anaerobic γ-proteobacterium Shewanella oneidensis MR-1 encodes for three terminal oxidases: a bd-type quinol oxidase and two heme-copper oxidases, a A-type cytochrome c oxidase and a cbb3-type oxidase. In this study, we used a biochemical approach and directly measured oxidase activities coupled to mass-spectrometry analysis to investigate the physiological role of the three terminal oxidases under aerobic and microaerobic conditions. Our data revealed that the cbb3-type oxidase is the major terminal oxidase under aerobic conditions while both cbb3-type and bd-type oxidases are involved in respiration at low-O2 tensions. On the contrary, the low O2-affinity A-type cytochrome c oxidase was not detected in our experimental conditions even under aerobic conditions and would therefore not be required for aerobic respiration in S. oneidensis MR-1. In addition, the deduced amino acid sequence suggests that the A-type cytochrome c oxidase is a ccaa3-type oxidase since an uncommon extra-C terminal domain contains two c-type heme binding motifs. The particularity of the aerobic respiratory pathway and the physiological implication of the presence of a ccaa3-type oxidase in S. oneidensis MR-1 are discussed. [ABSTRACT FROM AUTHOR]

Background: Efflux systems are involved in multidrug resistance in most Gram-negative non-fermentative bacteria. We have chosen Burkholderia thailandensis to dissect the development of multidrug resistance phenotypes under antibiotic pressure. Methodology/Principal Findings: We used doxycycline selection to obtain several resistant B. thailandensis variants. The minimal inhibitory concentrations of a large panel of structurally unrelated antibiotics were determined ± the efflux pump inhibitor phenylalanine-arginine ß-naphthylamide (PAßN). Membrane proteins were identified by proteomic method and the expressions of major efflux pumps in the doxycycline selected variants were compared to those of the parental strains by a quantitative RT-PCR analysis. Doxycycline selected variants showed a multidrug resistance in two major levels corresponding to the overproduction of two efflux pumps depending on its concentration: AmrAB-OprA and BpeEF-OprC. The study of two mutants, each lacking one of these pumps, indicated that a third pump, BpeAB-OprB, could substitute for the defective pump. Surprisingly, we observed antagonistic effects between PAßN and aminoglycosides or some ß-lactams. PAßN induced the overexpression of AmrAB-OprA and BpeAB-OprB pump genes, generating this unexpected effect. Conclusions/Significance: These results may account for the weak activity of PAßN in some Gram-negative species. We clearly demonstrated two antagonistic effects of this molecule on bacterial cells: the blocking of antibiotic efflux and an increase in efflux pump gene expression. Thus, doxycycline is a very efficient RND efflux pump inducer and PAßN may promote the production of some efflux pumps. These results should be taken into account when considering antibiotic treatments and in future studies on efflux pump inhibitors. [ABSTRACT FROM AUTHOR]

The concentration of CO2 in many aquatic systems is variable, often lower than the KM of the primary carboxylating enzyme Rubisco, and in order to photosynthesize efficiently, many algae operate a facultative CO2 concentrating mechanism (CCM). Here we measured the responses of a marine diatom, Thalassiosira pseudonana, to high and low concentrations of CO2 at the level of transcripts, proteins and enzyme activity. Low CO2 caused many metabolic pathways to be remodeled. Carbon acquisition enzymes, primarily carbonic anhydrase, stress, degradation and signaling proteins were more abundant while proteins associated with nitrogen metabolism, energy production and chaperones were less abundant. A protein with similarities to the Ca2+/ calmodulin dependent protein kinase II_association domain, having a chloroplast targeting sequence, was only present at low CO2. This protein might be a specific response to CO2 limitation since a previous study showed that other stresses caused its reduction. The protein sequence was found in other marine diatoms and may play an important role in their response to low CO2 concentration. [ABSTRACT FROM AUTHOR]

Background: Efflux systems are involved in multidrug resistance in most Gram-negative non-fermentative bacteria. We have chosen Burkholderia thailandensis to dissect the development of multidrug resistance phenotypes under antibiotic pressure. Methodology/Principal Findings: We used doxycycline selection to obtain several resistant B. thailandensis variants. The minimal inhibitory concentrations of a large panel of structurally unrelated antibiotics were determined ± the efflux pump inhibitor phenylalanine-arginine ß-naphthylamide (PAßN). Membrane proteins were identified by proteomic method and the expressions of major efflux pumps in the doxycycline selected variants were compared to those of the parental strains by a quantitative RT-PCR analysis. Doxycycline selected variants showed a multidrug resistance in two major levels corresponding to the overproduction of two efflux pumps depending on its concentration: AmrAB-OprA and BpeEF-OprC. The study of two mutants, each lacking one of these pumps, indicated that a third pump, BpeAB-OprB, could substitute for the defective pump. Surprisingly, we observed antagonistic effects between PAßN and aminoglycosides or some ß-lactams. PAßN induced the overexpression of AmrAB-OprA and BpeAB-OprB pump genes, generating this unexpected effect. Conclusions/Significance: These results may account for the weak activity of PAßN in some Gram-negative species. We clearly demonstrated two antagonistic effects of this molecule on bacterial cells: the blocking of antibiotic efflux and an increase in efflux pump gene expression. Thus, doxycycline is a very efficient RND efflux pump inducer and PAßN may promote the production of some efflux pumps. These results should be taken into account when considering antibiotic treatments and in future studies on efflux pump inhibitors. [ABSTRACT FROM AUTHOR]

The concentration of CO 2 in many aquatic systems is variable, often lower than the K M of the primary carboxylating enzyme Rubisco, and in order to photosynthesize efficiently, many algae operate a facultative CO 2 concentrating mechanism (CCM). Here we measured the responses of a marine diatom, Thalassiosira pseudonana, to high and low concentrations of CO 2 at the level of transcripts, proteins and enzyme activity. Low CO 2 caused many metabolic pathways to be remodeled. Carbon acquisition enzymes, primarily carbonic anhydrase, stress, degradation and signaling proteins were more abundant while proteins associated with nitrogen metabolism, energy production and chaperones were less abundant. A protein with similarities to the Ca 2+ / calmodulin dependent protein kinase II_association domain, having a chloroplast targeting sequence, was only present at low CO 2 . This protein might be a specific response to CO 2 limitation since a previous study showed that other stresses caused its reduction. The protein sequence was found in other marine diatoms and may play an important role in their response to low CO 2 concentration., Competing Interests: The authors declare no competing financial interests.

Bacterial pathogens often deliver effectors into host cells using type 3 secretion systems (T3SS), the extremity of which forms a translocon that perforates the host plasma membrane. The T3SS encoded by Salmonella pathogenicity island 1 (SPI-1) is genetically associated with an acyl carrier protein, IacP, whose role has remained enigmatic. In this study, using tandem affinity purification, we identify a direct protein-protein interaction between IacP and the translocon protein SipB. We show, by mass spectrometry and radiolabelling, that SipB is acylated, which provides evidence for a modification of the translocon that has not been described before. A unique and conserved cysteine residue of SipB is identified as crucial for this modification. Although acylation of SipB was not essential to virulence, we show that this posttranslational modification promoted SipB insertion into host-cell membranes and pore-forming activity linked to the SPI-1 T3SS. Cooccurrence of acyl carrier and translocon proteins in several γ- and β-proteobacteria suggests that acylation of the translocon is conserved in these other pathogenic bacteria. These results also indicate that acyl carrier proteins, known for their involvement in metabolic pathways, have also evolved as cofactors of new bacterial protein lipidation pathways., Competing Interests: The authors have declared that no competing interests exist.

The ability to respire sulfate linked to lactate oxidation is a key metabolic signature of the Desulfovibrio genus. Lactate oxidation by these incomplete oxidizers generates reductants through lactate dehydrogenase (LDH) and pyruvate-ferredoxin oxidoreductase (PFOR), with the latter catalyzing pyruvate conversion into acetyl-CoA. Acetyl-CoA is the source of substrate-level phosphorylation through the production of ATP. Here, we show that these crucial steps are performed by enzymes encoded by a nonacistronic transcriptional unit named now as operon luo (for lactate utilization operon). Using a combination of genetic and biochemical techniques, we assigned a physiological role to the operon genes DVU3027-28 and DVU3032-33. The growth of mutant Δ26-28 was highly disrupted on D-lactate, whereas the growth of mutant Δ32-33 was slower on L-lactate, which could be related to a decrease in the activity of D-lactate or L-lactate oxidase in the corresponding mutants. The DVU3027-28 and DVU3032-33 genes thus encode functional D-LDH and L-LDH enzymes, respectively. Scanning of the genome for lactate utilization revealed several lactate permease and dehydrogenase homologs. However, transcriptional compensation was not observed in any of the mutants except for lactate permease. Although there is a high degree of redundancy for lactate oxidase, it is not functionally efficient in LDH mutants. This result could be related to the identification of several operon enzymes, including LDHs, in the PFOR activity bands, suggesting the occurrence of a lactate-oxidizing supermolecular structure that can optimize the performance of lactate utilization in Desulfovibrio species.

We characterized the aro arsenite oxidation system in the novel strain Ralstonia sp. 22, a beta-proteobacterium isolated from soil samples of the Salsigne mine in southern France. The inducible aro system consists of a heterodimeric membrane-associated enzyme reacting with a dedicated soluble cytochrome c(554). Our biochemical results suggest that the weak association of the enzyme to the membrane probably arises from a still unknown interaction partner. Analysis of the phylogeny of the aro gene cluster revealed that it results from a lateral gene transfer from a species closely related to Achromobacter sp. SY8. This constitutes the first clear cut case of such a transfer in the Aro phylogeny. The biochemical study of the enzyme demonstrates that it can accommodate in vitro various cytochromes, two of which, c(552) and c(554,) are from the parent species. Cytochrome c(552) belongs to the sox and not the aro system. Kinetic studies furthermore established that sulfite and sulfide, substrates of the sox system, are both inhibitors of Aro activity. These results reinforce the idea that sulfur and arsenic metabolism are linked.