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See detailNatural functions of cyclic lipopeptides from Bacillus and Pseudomonas: more than surfactants and antibiotics
Raaijmakers, Jos; De Bruin, Irene; Nybroe, Ole et al

in FEMS Microbiology Reviews (2010), 34

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See detailThe Penicillin-Binding Proteins: Structure and Role in Peptidoglycan Biosynthesis
Sauvage, Eric ULg; Kerff, Frédéric ULg; Terrak, Mohammed ULg et al

in FEMS Microbiology Reviews (2008), 32(2), 234-58

Penicillin-binding proteins (PBPs) have been scrutinized for over 40 years. Recent structural information on PBPs together with the ongoing long-term biochemical experimental investigations, and results ... [more ▼]

Penicillin-binding proteins (PBPs) have been scrutinized for over 40 years. Recent structural information on PBPs together with the ongoing long-term biochemical experimental investigations, and results from more recent techniques such as protein localization by green fluorescent protein-fusion immunofluorescence or double-hybrid assay, have brought our understanding of the last stages of the peptidoglycan biosynthesis to an outstanding level that allows a broad outlook on the properties of these enzymes. Details are emerging regarding the interaction between the peptidoglycan-synthesizing PBPs and the peptidoglycan, their mesh net-like product that surrounds and protects bacteria. This review focuses on the detailed structure of PBPs and their implication in peptidoglycan synthesis, maturation and recycling. An overview of the content in PBPs of some bacteria is provided with an emphasis on comparing the biochemical properties of homologous PBPs (orthologues) belonging to different bacteria. [less ▲]

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See detailBacterial peptidoglycan (murein) hydrolases.
Vollmer, Waldemar; Joris, Bernard ULg; Charlier, Paulette ULg et al

in FEMS Microbiology Reviews (2008), 32(2), 259-86

Most bacteria have multiple peptidoglycan hydrolases capable of cleaving covalent bonds in peptidoglycan sacculi or its fragments. An overview of the different classes of peptidoglycan hydrolases and ... [more ▼]

Most bacteria have multiple peptidoglycan hydrolases capable of cleaving covalent bonds in peptidoglycan sacculi or its fragments. An overview of the different classes of peptidoglycan hydrolases and their cleavage sites is provided. The physiological functions of these enzymes include the regulation of cell wall growth, the turnover of peptidoglycan during growth, the separation of daughter cells during cell division and autolysis. Specialized hydrolases enlarge the pores in the peptidoglycan for the assembly of large trans-envelope complexes (pili, flagella, secretion systems), or they specifically cleave peptidoglycan during sporulation or spore germination. Moreover, peptidoglycan hydrolases are involved in lysis phenomena such as fratricide or developmental lysis occurring in bacterial populations. We will also review the current view on the regulation of autolysins and on the role of cytoplasm hydrolases in peptidoglycan recycling and induction of beta-lactamase. [less ▲]

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See detailXylanases, xylanase families and extremophilic xylanases
Collins, T.; Gerday, Charles ULg; Feller, Georges ULg

in FEMS Microbiology Reviews (2005), 29(1), 3-23

Xylanases are hydrolytic enzymes which randomly cleave the beta 1,4 backbone of the complex plant cell wall polysaccharide xylan. Diverse forms of these enzymes exist, displaying varying folds, mechanisms ... [more ▼]

Xylanases are hydrolytic enzymes which randomly cleave the beta 1,4 backbone of the complex plant cell wall polysaccharide xylan. Diverse forms of these enzymes exist, displaying varying folds, mechanisms of action, substrate specificities, hydrolytic activities (yields, rates and products) and physicochemical characteristics. Research has mainly focused on only two of the xylanase containing glycoside hydrolase families, namely families 10 and 11, yet enzymes with xylanase activity belonging to families 5, 7, 8 and 43 have also been identified and studied, albeit to a lesser extent. Driven by industrial demands for enzymes that can operate under process conditions, a number of extremophilic xylanases have been isolated, in particular those from thermophiles, alkaliphiles and acidiphiles, while little attention has been paid to cold-adapted xylanases. Here, the diverse physicochemical and functional characteristics, as well as the folds and mechanisms of action of all six xylanase containing families will be discussed. The adaptation strategies of the extremophilic xylanases isolated to date and the potential industrial applications of these enzymes will also be presented. [less ▲]

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See detailSome like it cold: biocatalysis at low temperatures
Georlette, D.; Blaise, Vinciane ULg; Collins, T. et al

in FEMS Microbiology Reviews (2004), 28(1), 25-42

In the last few years, increased attention has been focused on a class of organisms called psychrophiles. These organisms, hosts of permanently cold habitats, often display metabolic fluxes more or less ... [more ▼]

In the last few years, increased attention has been focused on a class of organisms called psychrophiles. These organisms, hosts of permanently cold habitats, often display metabolic fluxes more or less comparable to those exhibited by mesophilic organisms at moderate temperatures. Psychrophiles have evolved by producing, among other peculiarities, "cold-adapted" enzymes which have the properties to cope with the reduction of chemical reaction rates induced by low temperatures. Thermal compensation in these enzymes is reached, in most cases, through a high catalytic efficiency associated, however, with a low thermal stability. Thanks to recent advances provided by X-ray crystallography, structure modelling, protein engineering and biophysical studies, the adaptation strategies are beginning to be understood. The emerging picture suggests that psychrophilic enzymes are characterized by an improved flexibility of the structural components involved in the catalytic cycle, whereas other protein regions, if not implicated in catalysis, may be even more rigid than their mesophilic counterparts. Due to their attractive properties, i.e., a high specific activity and a low thermal stability, these enzymes constitute a tremendous potential for fundamental research and biotechnological applications. (C) 2003 Federation of European Microbiological Societies. Published by Elsevier B.V. All rights reserved. [less ▲]

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See detailEnzymes from psychrophilic organisms
Feller, Georges ULg; Narinx, E.; Arpigny, J. L. et al

in FEMS Microbiology Reviews (1996), 18(2-3), 189-202

Psychrophilic organisms such as micro-organisms and other ectothermic species living in polar, deep- sea or any constantly low temperature environments, produce enzymes adapted to function at low ... [more ▼]

Psychrophilic organisms such as micro-organisms and other ectothermic species living in polar, deep- sea or any constantly low temperature environments, produce enzymes adapted to function at low temperature. These enzymes are characterized by a high catalytic efficiency at low and moderate temperatures but are rather thermolabile. Due to their high specific activity and their rapid inactivation at temperatures as low as 30 degrees C, they offer, along with the producing micro-organisms, a great potential in biotechnology. The molecular basis of the adaptation of cold cu-amylase, subtilisin, triose phosphate isomerase from Antarctic bacteria and of trypsin from fish living in North Atlantic and in Antarctic sea waters have been studied. The comparison of the 3D structures obtained either by protein modelling or by X-ray crystallography (North Atlantic trypsin) with those of their mesophilic counterparts indicates that the molecular changes tend to increase the flexibility of the structure by a weakening of the intramolecular interactions and by an increase of the interactions with the solvent. For each enzyme, the most appropriate strategy enabling it to accommodate the substrate at a low energy cost is selected. There is a price to pay in terms of thermosensibility because the selective pressure is essentially oriented towards the harmonization of the specific activity with ambient thermal conditions. However, as demonstrated by site-directed mutagenesis experiments carried out on the Antarctic subtilisin, the possibility remains to stabilize the structure of these enzymes without affecting their high catalytic efficiency. [less ▲]

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See detailPlasmids for heavy metal resistance in Alcaligenes eutrophus CH34: Mechanisms and applications
Collard, Jean-Marc; Corbisier, Philippe; Diels, Ludo et al

in FEMS Microbiology Reviews (1994), 14

Alcaligenes eutrophus CH34 is the main representative of a group of strongly related strains (mostly facultative chemolithotrophs) that are well adapted to environments containing high levels of heavy ... [more ▼]

Alcaligenes eutrophus CH34 is the main representative of a group of strongly related strains (mostly facultative chemolithotrophs) that are well adapted to environments containing high levels of heavy metals. It harbors the megaplasmids pMOL28 and pMOL30 which carry resistance determinants to Co2+, Ni2+, CrO42-, Hg2+, Tl+, Cd2+, Cu2+ and Zn2+. Among the best characterized determinants are the cnr operon (resistance to Co, Ni) an pMOL28 and the czc operon on pMOL30 (resistance to Co, Cd and Zn). Although the two systems reveal a significant degree of amino acid similarity in the structural genes, the regulation of the operons is different. The resistance mechanism in both cases is based on efflux. The efflux mechanism leads to a pH increase outside of the cytoplasmic membrane. Metals are sequestered from the external medium through the bioprecipitation of metal carbonates formed in the saturated zone around the cell. This latter phenomenon can be exploited in bioreactors designed to remove metals from effluents. The bacteria are immobilized on composite membranes in a continuous tubular membrane reactor (CTMR). The effluent continuously circulates through the intertubular space, while the external surface of the tubes is in contact with the growth medium. Metal crystals are eventually removed by the effluent stream and collected on a glass bead column. The system has been applied to effluents containing Cd, Zn, Co, Ni and Cu. By introducing catabolic plasmids involved in the aerobic degradation of PCBs and 2,4-D into metal-resistant A. eutrophus strains, the application range was widened to include effluents polluted with both organic and inorganic substances. Biosensors have been developed which are based on the fusion of genes induced by metals to a reporter system, the lux operon of Vibrio fischeri. Bacterial luciferases produce light through the oxidation of fatty aldehydes. The gene fusions are useful both for the study of regulatory genes and for the determination of heavy metal concentrations in the environment. [less ▲]

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