CBMs carbohydrate binding

Clostridium thermocellum s cellulosome. CBM carbohydrate-binding module (Based on Gilbert 2007)... 

Aromatic amino acid side chains and their orientation play a crucial role in carbohydrate binding their specific interaction with the ligand is ubiquitous to CBM carbohydrate recognition. The side chains of tryptophan, tyrosine, and, less commonly, phenylalanine, form the hydrophobic platforms in CBM-binding sites, which can be planar, twisted, or form a sandwich (Boraston et al, 2004). 

Many glycosidases which attack insoluble or partly soluble polysaccharides have a modular construction, in which catalytic domains and carbohydrate binding modules (CBMs) are produced in the same polypeptide. Although there may be occasional exceptions, the main function of these domains appears to be to increase the local concentration of enzyme by loosely absorbing the enzyme to the substrate. CBMs have been classified into families on the basis of amino acid sequence, like the catalytic domains and are on CAZy, the continuously updated website in summer 2007 there were 49 families. Early work had concentrated on the cellulose binding domains (CBDs) previous classifications had referred to CBM (or CBD) Types and used Roman numerals and, to concur with this usage, CBM Families 1-13 are the same as CBM Types 1-XIII. 

CBM Family 13 adopt the p-trefoil fold first encountered with the ricin B (carbohydrate-binding) chain. It contains 12 strands of p-sheet arranged in such a way as to provide three independent sugar binding sites with different specificities, and again binding is enthalpy driven. 

Both enzymes have a family 1 CBM however, they differ in that the carbohydrate binding module is N-terminal in FaeA and C-terminal in FaeB (Fig 1). This situation mirrors that of Cel6A (N-terminal CBM) and Cel7A (C-terminal CBM) of T. reesei. The... 

More than 300 proteins are currently classified in the CAZy database, including glycoside hydrolases (GHs), glicosyltransferases (GTs), polysaccharide lyases (PLs) and carbohydrate esterases (CEs). Usually, CAZymes present a modular structure, nearly 7% of the enzymes having at least one carbohydrate-binding module [13]. CBMs are also classified... 

Ribeiro, T Ponte, PIP Guerreiro, CIPD Santos, HM Falcatildeo, L Freire, JPB et al. A family 11 carbohydrate-binding module (CBM) improves the efficacy of a recombinant cellulase used to supplement barley-based diets for broilers at lower dosage rates. British Poultry Science, 2008, 49(5), 600-8. 

Xu, Q Song, Q Ai, X McDonald, TJ Long, H Ding, S et al. Engineered carbohydrate-binding module (CBM) protein-suspended single-walled carbon nanotubes in water. Chem Commun., 2009, 337-9. 

Whereas the binding of CBMs to insoluble carbohydrates can be monitored by the UV absorption of the protein, relatively large amounts are required, and in some of the early studies on CBDs they were made radioactive with to increase sensitivity. The general technical problem of monitoring the binding of soluble, non-chromophoric ligands to soluble CBMs, has, however, been solved only in the last decade, with the advent of isothermal titration microcalorimetry... 

Functionally, CBMs can be divided into three types those which bind to the crystalline regions of solid polysaccharides and show weak, if any affinity for soluble carbohydrates (Type A) those which bind polysaccharide-chains, whether as soluble oligosaccharides or as amorphous regions of insoluble polysaccharides (Type B) and those which bind small sugar molecules (Type C). Unsurprisingly, there is considerable overlap between Type C CBMs and lectins, molecules which bind, but do not transform, sugars. 

A quantitative fluorimetric method for the analysis of crystalline cellulose on fiber surfaces was developed. This method quantitatively shows differences in crystalline cellulose binding sites of differently processed pulp fibers. The results indicated that CBMs provide useful, novel tools for monitoring changes in carbohydrate content of non uniform substrate surfaces, for example, during wood or pulping processes and possibly also during fiber biosynthesis [169],... 

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