Polysaccharides glycoside hydrolases

Glycoside hydrolases (glycosidases) are essential and consequently widely abundant enzymes in all living systems that rely on the processing of carbohydrates. From the degradation of such polysaccharides as starch, cellulose, or chitin to the highly... 

Polysaccharide lyases have been grouped into a number of CAZy families and mechanistic and structural data are available for a number of them. As with the glycoside hydrolases, enzymes of the same CAZy family have the same protein fold and similar, if not identical, mechanisms. In June 2007 there were 18 polysaccharide lyase families. 

Some excellent reviews have appeared extensively covering the enzymatic polymerization of polysaccharides using glycoside hydrolases [233-245]. Two examples of this field are highlighted below for more details please refer to these reviews. 

Biocatalysis is a key route to both natural and non-natural polysaccharide structures. Research in this area is particularly rich and generally involves at least one of the following three synthetic approaches 1) isolated enzyme, 2) whole-cell, and 3) some combination of chemical and enzymatic catalysts (i.e. chemoenzymatic methods) (87-90). Two elegant examples that used cell-fi-ee enzymatic catalysts were described by Makino and Kobayashi (25) and van der Vlist and Loos (27). Indeed, for many years, Kobayashi has pioneered the use of glycosidic hydrolases as catalysts for polymerizations to prepare polysaccharides (88,91). In their paper, Makino and Kobayashi (25) made new monomers and synthesized unnatural hybrid polysaccharides with regio- and stereochemical-control. Van der Vlist and Loos (27) made use of tandem reactions catalyzed by two different enzymes in order to prepare branched amylose. One enzyme catalyzed the synthesis of linear structures (amylose) where the second enzyme introduced branches. In this way, artificial starch can be prepared with controlled quantities of branched regions. 

A number of glycosidic hydrolases have been produced in sufficiently pure form to allow the development of a method of determination of monosaccharide sequences based on these enzymes (Table 6.4). These enzymes will remove specific monosaccharide units linked by specific linkages from the nonreducing end of a polysaccharide. For example, P-galactosidase will remove D-galactosyl residues linking p-glycosidically to polysaccharide. The use of sequential enzymatic hydrolysis is a well-established technique, particularly for the analysis of the carbohydrate residues of macromolecules. 

Since this is a book on nomenclature, it is a pity that Enzyme Nomenclature does not necessarily use nomenclature currently accepted on an official basis elsewhere. A good example is the area of glycoside hydrolases hydrolysing 0-glycosyl compounds where the recommended nomenclature is sometimes based on polysaccharide structure of the substrate, and sometimes on a trivial name non-indicative of substrate structure. Furthermore, exo- and e do-acting polysaccharide hydrolases are not necessarily distinguished, and in a few instances a singular enzyme activity is covered by more than one EC number. 

L.L., Blumer-Schuette, S.E., and Kelly, R.M. (2016) Multi domain, surface layer-associated glycoside hydrolases contribute to plant polysaccharide degradation by Ceddicdlulosiruptor species. / Biol Chem., 291, 6732—6747. 

Polysaccharide monoojygenases have long been classified as Glycoside Hydrolase family 61 (GH-61) because weak endoglucanase activity had been observed. These experimental results might be explained by the fact that chain breaks introduced near the reducing end will release soluble native cello-oligosaccharides. Nevertheless, this classification is incorrect since an... 

As with glycoside hydrolases, the polysaccharide lyases (PL) have long been classified into sequence-related protein families (129) in the CAZy database (28). Presently, more than 20 PL families are listed in CAZy, and, because of significant recent attention, at least one three-dimensional structural representative is known for approximately one half of these (reviewed in Refe. (126,127), and (130) see also http //www.cazy.org/fam/acc PL.html). Not surprisingly, these endo-acting enzymes possess cleft-shaped active sites (126), akin to the polysaccharide erac/o-glycosidases vide supra). Characteristically, polysaccharide lyases bind their polyanionic substrates through basic amino acid residues and/or Ca++ ion complexation. Indeed, the activity of nearly all known pectate lyases strictly requires Ca++, which in some cases may directly affect the catalysis (126). 

A review of enzyme analysers has described the automation of fixed-time and continuous-monitoring assays and the uses of partly or completely automated analysers and multi-channel systems. Automated analyses of polysaccharide hydrolases, in soluble or insoluble form, have been based on determination of the liberated reducing sugars with 3,5-dinitrosalicylic acid. A sensitive and specific method for locating glycoside hydrolases (e.g. oc-D-mannosidases) in polyacryl-... 

Properties.— The properties of glycoside hydrolases have been reviewed. As part of a series on surface carbohydrates of the prokaryotic cell, a comprehensive chapter deals with enzymes acting on bacterial surface carbohydrates. Enzymes hydrolysing capsular and slime polysaccharides, lipopolysaccharides, and teichoic acids are treated in detail. 

Glycoside hydrolases cleave the glycosidic bond in polysaccharides like starch, inulin, cellulose and their derivatives. The most important types are (a) the amylases (EC 3.2.1.1 and EC 3.2.1.2), which act on starch and derived polysaccharides to hydrolyse the a-1,4 and/or a-1,6 glucoside linkages, and (b) cellulase (EC 3.2.1.4), which act on (3-1,4 glucoside linkages in cellulose and derived polymers. 

Cellulolysis breaks down cellulose into smaller polysaccharides (cel-lodextrins) or into glucose units using glycoside hydrolase enzymes. These include endo-acting cellulases and exo-acting glucosidases. Such enzymes are usually secreted as part of multienzyme complexes. Cellulolysis is relatively difficult compared to the breakdown of other polysaccharides, due to the secondary/tertiary structure of cellulose. 

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