M. L. Sinnott

Bio: M. L. Sinnott is an academic researcher from University of Illinois at Urbana–Champaign. The author has contributed to research in topics: Glycosyl. The author has an hindex of 1, co-authored 1 publications receiving 142 citations.

Molecular and biotechnological aspects of xylanases

Abstract: Hemicellulolytic microorganisms play a significant role in nature by recycling hemicellulose, one of the main components of plant polysaccharides. Xylanases (EC 3.2.1.8) catalyze the hydrolysis of xylan, the major constituent of hemicellulose. The use of these enzymes could greatly improve the overall economics of processing lignocellulosic materials for the generation of liquid fuels and chemicals. Recently cellulase-free xylanases have received great attention in the development of environmentally friendly technologies in the paper and pulp industry. In microorganisms that produce xylanases low molecular mass fragments of xylan and their positional isomers play a key role in regulating its biosynthesis. Xylanase and cellulase production appear to be regulated separately, although the pleiotropy of mutations, which causes the elimination of both genes, suggests some linkage in the synthesis of the two enzymes. Xylanases are found in a cornucopia of organisms and the genes encoding them have been cloned in homologous and heterologous hosts with the objectives of overproducing the enzyme and altering its properties to suit commercial applications. Sequence analyses of xylanases have revealed distinct catalytic and cellulose binding domains, with a separate non-catalytic domain that has been reported to confer enhanced thermostability in some xylanases. Analyses of three-dimensional structures and the properties of mutants have revealed the involvement of specific tyrosine and tryptophan residues in the substrate binding site and of glutamate and aspartate residues in the catalytic mechanism. Many lines of evidence suggest that xylanases operate via a double displacement mechanism in which the anomeric configuration is retained, although some of the enzymes catalyze single displacement reactions with inversion of configuration. Based on a dendrogram obtained from amino acid sequence similarities the evolutionary relationship between xylanases is assessed. In addition the properties of xylanases from extremophilic organisms have been evaluated in terms of biotechnological applications.

Substrate and Enzyme Characteristics that Limit Cellulose Hydrolysis

Abstract: The ability and, consequently, the limitations of various microbial enzyme systems to completely hydrolyze the structural polysaccharides of plant cell walls has been the focus of an enormous amount of research over the years. As more and more of these extracellular enzymatic systems are being identified and characterized, clear similarities and differences are being elucidated. Although much has been learned concerning the structures, kinetics, catalytic action, and interactions of enzymes and their substrates, no single mechanism of total lignocellulosic saccharification has been established. The heterogeneous nature of the supramolecular structures of naturally occurring lignocellulosic matrices make it difficult to fully understand the interactions that occur between enzyme complexes and these substrates. However, it is apparent that the efficacy of enzymatic complexes to hydrolyze these substrates is inextricably linked to the innate structural characteristics of the substrate and/or the modifications that occur as saccharification proceeds. This present review is not intended to conclusively answer what factors control polysaccharide biodegradation, but to serve as an overview illustrating some of the potential enzymatic and structural limitations that invariably influence the complete hydrolysis of lignocellulosic polysaccharides.

Myrosinase: gene family evolution and herbivore defense in Brassicaceae.

Abstract: Glucosinolates are a category of secondary products present primarily in species of the order Capparales. When tissue is damaged, for example by herbivory, glucosinolates are degraded in a reaction catalyzed by thioglucosidases, denoted myrosinases, also present in these species. Thereby, toxic compounds such as nitriles, isothiocyanates, epithionitriles and thiocyanates are released. The glucosinolate-myrosinase system is generally believed to be part of the plant's defense against insects, and possibly also against pathogens. In this review, the evolution of the system and its impact on the interaction between plants and insects are discussed. Further, data suggesting additional functions in the defense against pathogens and in sulfur metabolism are reviewed.

Potential and utilization of thermophiles and thermostable enzymes in biorefining

Abstract: In today's world, there is an increasing trend towards the use of renewable, cheap and readily available biomass in the production of a wide variety of fine and bulk chemicals in different biorefineries. Biorefineries utilize the activities of microbial cells and their enzymes to convert biomass into target products. Many of these processes require enzymes which are operationally stable at high temperature thus allowing e.g. easy mixing, better substrate solubility, high mass transfer rate, and lowered risk of contamination. Thermophiles have often been proposed as sources of industrially relevant thermostable enzymes. Here we discuss existing and potential applications of thermophiles and thermostable enzymes with focus on conversion of carbohydrate containing raw materials. Their importance in biorefineries is explained using examples of lignocellulose and starch conversions to desired products. Strategies that enhance thermostablity of enzymes both in vivo and in vitro are also assessed. Moreover, this review deals with efforts made on developing vectors for expressing recombinant enzymes in thermophilic hosts.

Multidomain architecture of beta-glycosyl transferases: implications for mechanism of action.

Abstract: INDER M. SAXENA, R. MALCOLM BROWN, JR., MICHEL FEVRE, ROBERTO A. GEREMIA, AND BERNARD HENRISSAT* Department of Botany, University of Texas, Austin, Texas 78713-7640; Laboratoire de Biologie Cellulaire Fongique, Centre de Génétique Moléculaire et Cellulaire, Université Claude Bernard, 43 Bd du 11 Novembre 1918, 69622 Villeurbanne cedex, France; and Centre de Recherches sur les Macromolécules Végétales, CNRS, BP 53, 38041 Grenoble cedex 9, France