The last piece in the cellulase puzzle: the characterisation of beta-glucosidase from the herbivorous gecarcinid land crab Gecarcoidea natalis.
A 160 kDa enzyme with beta-glucosidase activity was purified from the midgut gland of the land crab Gecarcoidea natalis. The enzyme was capable of releasing glucose progressively from cellobiose, cellotriose or cellotetraose. Although beta-glucosidases (EC 3.2.1.21) have some activity towards substrates longer than cellobiose, the enzyme was classified as a glucohydrolase (EC 3.2.1.74) as it had a preference for larger substrates (cellobiose<cellotriose=cellotetraose). It was able to synthesise some cellotetraose by the transglycosylation of smaller substrates - another common feature of glucohydrolases. The interaction between the glucohydrolase described here and the endo-beta-1,4-glucanases described previously for G. natalis provides a complete model for cellulose hydrolysis in crustaceans and possibly in other invertebrates. After mechanical fragmentation by the gastric mill, multiple endo-beta-1,4-glucanases would initially cleave beta-1,4-glycosidic bonds within native cellulose, releasing small oligomers, including cellobiose, cellotriose and cellotetraose. The glucohydrolase would then attach to these oligomers, progressively releasing glucose. The glucohydrolase might also attach directly to crystalline cellulose to release glucose from free chain ends. This two-enzyme system differs from the traditional model, which suggests that total cellulose hydrolysis requires the presence an endo-beta-1,4-glucanse, a cellobiohydrolase and a beta-glucosidase.
Allardyce
Benjamin J
BJ
School of Life and Environmental Sciences, Deakin University, Pigdons Road, Geelong, Victoria, 3217, Australia. balla@deakin.edu.au
Linton
Stuart M
SM
Saborowski
Reinhard
R
D000818:Animals; D003386:Brachyura / Q000201:enzymology*; D002850:Chromatography, Gel; D002852:Chromatography, Ion Exchange; D002853:Chromatography, Liquid; D002855:Chromatography, Thin Layer; D004064:Digestive System / Q000201:enzymology; D004591:Electrophoresis, Polyacrylamide Gel; D005247:Feeding Behavior / Q000502:physiology*; D005947:Glucose / Q000378:metabolism; D006868:Hydrolysis; D057927:Hydrophobic and Hydrophilic Interactions; D008954:Models, Biological; D009844:Oligosaccharides / Q000378:metabolism; D013194:Staining and Labeling; D014020:Tissue Extracts / Q000378:metabolism; D001617:beta-Glucosidase / Q000302:isolation & purification / Q000378:metabolism*
D009844:Oligosaccharides; D014020:Tissue Extracts; D001617:beta-Glucosidase; D005947:Glucose