Structural and Functional Characterization of a Lytic Polysaccharide Monooxygenase with Broad Substrate Specificity

The recently discovered lytic polysaccharide monooxygenases (LPMOs) carry out oxidative cleavage of polysaccharides and are of major importance for efficient processing of biomass. NcLPMO9C from Neurospora crassa acts both on cellulose and on non-cellulose β-glucans, including cellodextrins and xyloglucan. The crystal structure of the catalytic domain of NcLPMO9C revealed an extended, highly polar substrate-binding surface well suited to interact with a variety of sugar substrates. The ability of NcLPMO9C to act on soluble substrates was exploited to study enzyme-substrate interactions. EPR studies demonstrated that the Cu2+ center environment is altered upon substrate binding, whereas isothermal titration calorimetry studies revealed binding affinities in the low micromolar range for polymeric substrates that are due in part to the presence of a carbohydrate-binding module (CBM1). Importantly, the novel structure of NcLPMO9C enabled a comparative study, revealing that the oxidative regioselectivity of LPMO9s (C1, C4, or both) correlates with distinct structural features of the copper coordination sphere. In strictly C1-oxidizing LPMO9s, access to the solvent-facing axial coordination position is restricted by a conserved tyrosine residue, whereas access to this same position seems unrestricted in C4-oxidizing LPMO9s. LPMO9s known to produce a mixture of C1- and C4-oxidized products show an intermediate situation

Institutions and Semantic Networks

61 σ.Παρουσιάζονται η θεωρίας των institutions καθώς και η έννοια του σημασιολογικού δικτύου και αποδεικνύεται ότι τα σημασιολογικά δίκτυα σχηματίζουν ένα institution.We present the theory of institutions and the concept of semantic network and prove that semantic networks form an institution.Μαρία Μ. Δημαρόγκων

Marine-derived biocatalysts: Importance, accessing, and application in aromatic pollutant bioremediation

The aim of the present review is to highlight the potential use of marine biocatalysts (whole cells or enzymes) as an alternative bioprocess for the degradation of aromatic pollutants. Firstly, information about the characteristics of the still underexplored marine environment and the available scientific tools used to access novel marine-derived biocatalysts is provided. Marine-derived enzymes, such as dioxygenases and dehalogenases, and the involved catalytic mechanisms for the degradation of aromatic and halogenated compounds, are presented, with the purpose of underpinning their potential use in bioremediation. Emphasis is given on persistent organic pollutants (POPs) that are organic compounds with significant impact on health and environment due to their resistance in degradation. POPs bioaccumulate mainly in the fatty tissue of living organisms, therefore current efforts are mostly focused on the restriction of their use and production, since their removal is still unclear. A brief description of the guidelines and criteria that render a pollutant POP is given, as well as their potential biodegradation by marine microorganisms by surveying recent developments in this rather unexplored field. © 2017 Nikolaivits, Dimarogona, Fokialakis and Topakas

Lignin boosts the cellulase performance of a GH-61 enzyme from Sporotrichum thermophile

An enzyme belonging to the glycoside hydrolase family 61 from the thermophilic fungus Sporotrichum thermophile, was functionally expressed in the methylotrophic yeast Pichia pastoris under the transcriptional control of the alcohol oxidase (AOX1) promoter. The enzyme hydrolyzed barley beta-glucan, carboxymethyl cellulose, lichenan, wheat arabinoxylan and birchwood xylan showing optimal activity at pH 8 and 65 degrees C. A 2:1 mixture of Celluclast 1.5 L and StCel61a was capable of increasing the degree of spruce conversion by 42%. The use of substrates with varying lignin content permitted the detection of a dependence of the enhancing capacity of StCel61a on the radical scavenging capacity of the different lignocellulosics. In the presence of a reductant, StCel61a boosted the efficiency of a mixture of purified cellulases (EGII, CBHI, beta-GLUC) by 20%. The synergistic activity exhibited by StCel61a and its dependence on reducing substances provide guidelines for process design towards the production of economically viable bioethanol

Marine-derived biocatalysts: Importance, accessing, and application in aromatic pollutant bioremediation

The aim of the present review is to highlight the potential use of marine biocatalysts (whole cells or enzymes) as an alternative bioprocess for the degradation of aromatic pollutants. Firstly, information about the characteristics of the still underexplored marine environment and the available scientific tools used to access novel marine-derived biocatalysts is provided. Marine-derived enzymes, such as dioxygenases and dehalogenases, and the involved catalytic mechanisms for the degradation of aromatic and halogenated compounds, are presented, with the purpose of underpinning their potential use in bioremediation. Emphasis is given on persistent organic pollutants (POPs) that are organic compounds with significant impact on health and environment due to their resistance in degradation. POPs bioaccumulate mainly in the fatty tissue of living organisms, therefore current efforts are mostly focused on the restriction of their use and production, since their removal is still unclear. A brief description of the guidelines and criteria that render a pollutant POP is given, as well as their potential biodegradation by marine microorganisms by surveying recent developments in this rather unexplored field. © 2017 Nikolaivits, Dimarogona, Fokialakis and Topakas