The starch‐binding domain from glucoamylase disrupts the structure of starch

Southall, Stacey M.; Simpson, P. J.; Gilbert, Harry J.; Williamson, Gary; Williamson, Michael P.

doi:10.1016/s0014-5793(99)00263-x

Cited by 149 publications

(125 citation statements)

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“…In some of the 59 CBM families, exemplified by CBM1, CBM10, and CBM20, ligand specificity is invariant (Linder and Teeri, 1997;Southall et al, 1999;Raghothama et al, 2000), while in some families, such as CBM6 (Czjzek et al, 2001;Pires et al, 2004), CBM4 (Boraston et al, 2002b), and CBM35 (Tunnicliffe et al, 2005;Montanier et al, 2009b), carbohydrate recognition is highly variable. In addition to defining a phylogenetic relationship between CBMs by clustering these modules into sequence-based families, they have also been classified into three categories (types A, B, and C) based on the topology of their ligand-binding sites and their mode of ligand recognition (for review, see Boraston et al, 2004; Fig.…”

Section: Cbmsmentioning

confidence: 99%

The Biochemistry and Structural Biology of Plant Cell Wall Deconstruction

2010

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Section: Cbmsmentioning

confidence: 99%

The Biochemistry and Structural Biology of Plant Cell Wall Deconstruction

2010

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“…Although many of these modules target components of the plant cell wall, several CBM families contain proteins that bind to insoluble storage polysaccharides such as starch and glycogen. Indeed, the structure and biochemistry of several family 20 CBMs, which bind to starch, have been analysed extensively (see [6][7][8][9][10][11][12][13] for examples). Furthermore, numerous crystal structures of starch-modifying enzymes have revealed malto-oligosaccharide-binding sites that are distinct from the substrate-binding cleft, indicating that these enzymes also contain starch-binding CBMs [14][15][16][17].…”

Section: Introductionmentioning

confidence: 99%

Carbohydrate-binding modules: fine-tuning polysaccharide recognition

Boraston

Bolam

Gilbert

et al. 2004

Biochemical Journal

1,777

1,724

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The enzymic degradation of insoluble polysaccharides is one of the most important reactions on earth. Despite this, glycoside hydrolases attack such polysaccharides relatively inefficiently as their target glycosidic bonds are often inaccessible to the active site of the appropriate enzymes. In order to overcome these problems, many of the glycoside hydrolases that utilize insoluble substrates are modular, comprising catalytic modules appended to one or more non-catalytic CBMs (carbohydrate-binding modules). CBMs promote the association of the enzyme with the substrate. In view of the central role that CBMs play in the enzymic hydrolysis of plant structural and storage polysaccharides, the ligand specificity displayed by these protein modules and the mechanism by which they recognize their target carbohydrates have received considerable attention since their discovery almost 20 years ago. In the last few years, CBM research has harnessed structural, functional and bioinformatic approaches to elucidate the molecular determinants that drive CBM-carbohydrate recognition. The present review summarizes the impact structural biology has had on our understanding of the mechanisms by which CBMs bind to their target ligands.

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“…In contrast, it was initially believed that CBMs may disrupt the ordered structure of recalcitrant crystalline substrates such as cellulose, leading to increased enzyme access and hence catalytic activity (28,29). Over the last quarter of a century, however, there have been only three reports of CBMs mediating modest (0.5-to fourfold) potentiation of enzyme activity in trans, pointing to a possible substrate disruption mechanism (30)(31)(32). However, the possibility of the formation of noncovalent CBM/enzyme interactions, which would argue in favor of a targeting function for the CBMs, was not explored.…”

Section: Discussionmentioning

confidence: 99%

How nature can exploit nonspecific catalytic and carbohydrate binding modules to create enzymatic specificity

Cuskin

Flint

Gloster

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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Noncatalytic carbohydrate binding modules (CBMs) are components of glycoside hydrolases that attack generally inaccessible substrates. CBMs mediate a two-to fivefold elevation in the activity of endoacting enzymes, likely through increasing the concentration of the appended enzymes in the vicinity of the substrate. The function of CBMs appended to exo-acting glycoside hydrolases is unclear because their typical endo-binding mode would not fulfill a targeting role. Here we show that the Bacillus subtilis exo-acting β-fructosidase SacC, which specifically hydrolyses levan, contains the founding member of CBM family 66 (CBM66). The SacC-derived CBM66 (BsCBM66) targets the terminal fructosides of the major fructans found in nature. The crystal structure of BsCBM66 in complex with ligands reveals extensive interactions with the terminal fructose moiety (Fru-3) of levantriose but only limited hydrophobic contacts with Fru-2, explaining why the CBM displays broad specificity. Removal of BsCBM66 from SacC results in a ∼100-fold reduction in activity against levan. The truncated enzyme functions as a nonspecific β-fructosidase displaying similar activity against β-2,1-and β-2,6-linked fructans and their respective fructooligosaccharides. Conversely, appending BsCBM66 to BT3082, a nonspecific β-fructosidase from Bacteroides thetaiotaomicron, confers exolevanase activity on the enzyme. We propose that BsCBM66 confers specificity for levan, a branched fructan, through an "avidity" mechanism in which the CBM and the catalytic module target the termini of different branches of the same polysaccharide molecule. This report identifies a unique mechanism by which CBMs modulate enzyme function, and shows how specificity can be tailored by integrating nonspecific catalytic and binding modules into a single enzyme.isothermal titration calorimetry | X-ray crystallography | prebiotics | biofuels | lectins C omplex carbohydrates represent a major nutrient for numerous microbial ecosystems, exemplified by bacterial and fungal communities established in the rumen and large bowel of mammals, where they play an important role in animal nutrition and human health, respectively (1, 2). It is also evident that these composite structures are of increasing industrial significance, particularly in the bioenergy and bioprocessing sectors (3). The enzymes that catalyze the degradation of these complex carbohydrates, primarily glycoside hydrolases but also polysaccharide lyases, are grouped into sequence-based families on the continuously updated CAZy database (4). Members of the same family display a common fold, and the catalytic mechanism and catalytic apparatus are also conserved (5). Substrate specificity within glycoside hydrolase families (GHs), however, can vary significantly (6). Glycanases that attack inaccessible substrates often contain noncatalytic carbohydrate binding modules (CBMs; see ref. 7 for review) that are also grouped into sequence-based families in the CAZy database. Against recalcitrant substrates, CBMs enhance the activit...

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The starch‐binding domain from glucoamylase disrupts the structure of starch

Cited by 149 publications

References 20 publications

The Biochemistry and Structural Biology of Plant Cell Wall Deconstruction

The Biochemistry and Structural Biology of Plant Cell Wall Deconstruction

Carbohydrate-binding modules: fine-tuning polysaccharide recognition

How nature can exploit nonspecific catalytic and carbohydrate binding modules to create enzymatic specificity

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