Erwinia chrysanthemi exports degradative enzymes by using a type I protein secretion system. The proteases secreted by this system lack an N-terminal signal peptide but contain a C-terminal secretion signal. To explore the substrate specificity of this system, we have expressed the E. chrysanthemi transporter system (prtDEF genes) in Escherichia coli and tested the ability of this ABC transporter to export hybrid proteins carrying C-terminal fragments of E. chrysanthemi protease B. The C terminus contains six glycine-rich repeated motifs, followed by two repeats of the sequences DFLV and DIIV. Two types of hybrid proteins were assayed for transport, proteins with the 93-residue-protease-B C terminus containing one glycine-rich repeat and both hydrophobic terminal repeats and proteins with the 181-residue C terminus containing all repeat motifs. Although the shorter C terminus is unable to export the hybrids, the longer C terminus can promote the secretion of hybrid proteins with N termini as large as 424 amino acids, showing that the glycine-rich motifs are required for the efficient secretion of these hybrids. However, the secretion of hybrids occurs only if these proteins do not carry disulfide bonds in their mature structures. These latter results suggest that disulfide bond formation can occur prior to or during the secretion. Disulfide bonds may prevent type I secretion of hybrids. One simple hypothesis to explain these results is that the type I channel is too narrow to permit the export of proteins with secondary structures stabilized by disulfide bonds.Nonpathogenic strains of Escherichia coli, such as the laboratory strain E. coli K-12, export few proteins to the external medium (53). The secretion of proteins in E. coli depends on a type II (Sec-dependent) mechanism in which unfolded proteins carrying an N-terminal signal sequence are transported across the inner membrane to the periplasm and then processed and folded in the periplasm prior to their translocation across the outer membrane. To initiate type II secretion, it is thought that a polypeptide and its signal peptide must be fully extended to cross the inner membrane (3). After crossing the inner membrane, proteins are folded in the periplasm in a process assisted by chaperones. In addition, the periplasm contains the enzymes required for the correct assembly of disulfide bonds to complete protein folding (5, 48).In contrast, many gram-negative pathogens including enteropathogenic E. coli (38), Yersinia spp. (36), Salmonella enterica serovar Typhimurium (39), and Vibrio cholerae (35) export virulence factors required for host colonization and survival. These virulence factors are secreted by mechanisms that operate independently from the type II system, mechanisms that involve specialized membrane transport apparatuses (64). A subset of virulence factors is exported by a type I mechanism in which three proteins assemble to form a transmembrane structure that couples the export of protein substrates with ATP hydrolysis. These ABC transporters in...
The analysis of the food environment is used to identify areas with gaps in the availability of healthy foods and can be used as a public policy assessment tool. In recent decades, Chile has implemented several strategies and regulations to improve food environments, with encouraging results. Little is known about the scope of these measures in socially vulnerable environments. This study is part of a project that seeks to build an integrated intervention model for healthy school environments in a vulnerable area of Santiago, Chile. The objective of this study was to evaluate the availability of healthy and unhealthy foods around schools and the relationship between it and socioeconomic determinants of the school community in the Chilean context. A cross-sectional study to measure the food environment of informal markets (street food), formal markets (stores), and institutions (schools) was conducted in and around 12 schools (100 m surrounding schools) in a vulnerable urban area of Santiago, Chile. A lack of healthy foods was observed, which was related to some socio-economic determinants and the multidimensional poverty was the most relevant. The diagnosis of food environments around schools can represent an important target for governments to implement policies focused at improving the availability of healthy foods.
Peroxisomes are thought to be formed by division of pre-existing peroxisomes after the import of newly synthesized proteins. However, it has been recently suggested that the endoplasmic reticulum (ER) provides an alternative de novo mechanism for peroxisome biogenesis in some cells. To test a possible role of the ERGolgi transit in peroxisome biogenesis in mammalian cells, we evaluated the biogenesis of three peroxisomal membrane proteins (PMPs): ALDRP (adrenoleukodystrophy related protein), PMP70 and Pex3p in CHO cells. We constructed chimeric genes encoding these PMPs and green fluorescent protein (GFP), and transiently transfected them to wild type and mutant CHO cells, in which normal peroxisomes were replaced by peroxisomal membrane ghosts. The expressed proteins were targeted to peroxisomes and peroxisomal ghosts correctly in the presence or absence of Brefeldin A (BFA), a drug known to block the ER-Golgi transit. Furthermore, low temperature did not disturb the targeting of Pex3p-GFP to peroxisomes. We also constructed two chimeric proteins of PMPs containing an ER retention signal "DEKKMP": GFP-ALDRP-DEKKMP and myc-Pex3p-DEKKMP. These proteins were mostly targeted to peroxisomes. No colocalization with an ER maker was found. These results suggest that the classical ER-Golgi pathway does not play a major role in the biogenesis of mammalian PMPs.
Chitin is one of the most abundant natural polysaccharides in the world and it is mainly used to produce chitosan by a deacetylation process. In the present study, the extraction of chitin and chitosan from the Parastacus pugnax (P. pugnax) crayfish exoskeleton was studied for the first time. Thus, the P. pugnax crayfish exoskeleton was converted to chitosan following the steps of depigmentation, deproteinization, and deacetylation. The produced chitosan (Chitosan-CGNA) was characterized in terms of the protein content, solubility, degree of deacetylation, viscosity, molecular weight, FTIR, SEM, XRD, antimicrobial, and antioxidant activity. The results showed that the obtained chitosan had a high degree of deacetylation (91.55%) and a medium molecular weight (589.43 kDa). The antibacterial activity of the chitosan was tested against bacterial strains relevant for the food industry and the lowest minimum inhibitory concentration (MIC) values were evidenced with Salmonella tiphymurium (S. typhimurium), Staphylococcus aureus (S. aureus), Enterococcus faecalis (E. faecalis) and Listeria. Monocytogenes (L. monocytogenes). Moreover, the Chitosan-CGNA showed an effect on DPPH radical scavenging activity, and its antioxidant activity was dependent on concentration and deacetylation degree. These results suggest that P. pugnax exoskeleton could be an excellent natural source for the production of chitosan with potential applications in the health system, and to prevent infections associated with pathogens strains.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.