Transglycosylases

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• Author: Spencer Williams
• Responsible Curator: Spencer Williams

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Overview

Transglycosylases are a class of GH enzymes that can catalyze the transformation of one glycoside to another. That is, these enzymes catalyze the substitution of a glycoside with another aglycon. Mechanistically, transglycosylases utilize the same mechanism as various retaining glycoside hydrolases. Thus, reaction of the nucleophile of a retaining glycoside hydrolase with a substrate gives a glycosyl-enzyme intermediate that can be intercepted either by water to give the hydrolysis product, or by another acceptor (often another carbohydrate alcohol), to give a new glycoside or oligosaccharide [1]. Alternatively, transglycosylation can occur by neighboring group participation, wherein a neighboring 2-acetamido group participates in the reaction to generate an oxazolinium ion intermediate, which can react with another acceptor other than water. Some transglycosidases possess substantial glycoside hydrolase activity, and some glycoside hydrolases possess transglycosylases activity. Indeed, in many cases it is unclear what the major role of an enzyme that possesses both activities may be. Transglycosylases are classified as glycoside hydrolases into various GH families on the basis of sequence similarity.

Generalized mechanism of a transglycosylase. Enzymatic cleavage of a substrate through a classical Koshland retaining mechanism results in formation of a glycosyl enzyme intermediate. This can partition to react with either water to cause hydrolysis (glycoside hydrolase activity) or to an alternative acceptor, often a sugar, to cause transglycosylation (transglycosylase activity).

Families

GH families with notable transglycosylase activity include:

• GH2, for example LacZ β-galactosidase converts lactose to allolactose [2].
  
• GH13, for example cyclodextran glucanotransferases that convert linear amylose to cyclodextrins[3]; glycogen debranching enzyme, which transfers three glucose residues from the four-residue glycogen branch to a nearby branch [4]; and trehalose synthase, which catalyzes the interconversion of maltose and trehalose [5].
  
• GH16, for example xyloglucan endotransglycosylases, which cuts and rejoins xyloglucan chains in the plant cell wall [6].
• GH31, for example, α-transglucosidases, which catalyze the transfer of individual glucosyl residues between α-(1→4)-glucans [7].
• GH70, for example glucansucrases, which catalyse the synthesis of high molecular weight glucans, from sucrose [8].
• GH77, for examples amylomaltase, which catalyzes the synthesis of maltodextrins from maltose.
• GH23, GH102, GH103, and GH104 lytic transglycosylases, which convert peptidoglycan to 1,6-anhydrosugars.

References

1. Crout DH and Vic G. (1998). Glycosidases and glycosyl transferases in glycoside and oligosaccharide synthesis. Curr Opin Chem Biol. 1998;2(1):98-111. DOI:10.1016/s1367-5931(98)80041-0 |
2. Juers DH, Matthews BW, and Huber RE. (2012). LacZ β-galactosidase: structure and function of an enzyme of historical and molecular biological importance. Protein Sci. 2012;21(12):1792-807. DOI:10.1002/pro.2165 |
3. Uitdehaag JC, Mosi R, Kalk KH, van der Veen BA, Dijkhuizen L, Withers SG, and Dijkstra BW. (1999). X-ray structures along the reaction pathway of cyclodextrin glycosyltransferase elucidate catalysis in the alpha-amylase family. Nat Struct Biol. 1999;6(5):432-6. DOI:10.1038/8235 |
4. Braun C, Lindhorst T, Madsen NB, and Withers SG. (1996). Identification of Asp 549 as the catalytic nucleophile of glycogen-debranching enzyme via trapping of the glycosyl-enzyme intermediate. Biochemistry. 1996;35(17):5458-63. DOI:10.1021/bi9526488 |
5. Zhang R, Pan YT, He S, Lam M, Brayer GD, Elbein AD, and Withers SG. (2011). Mechanistic analysis of trehalose synthase from Mycobacterium smegmatis. J Biol Chem. 2011;286(41):35601-35609. DOI:10.1074/jbc.M111.280362 |
6. Rose JK, Braam J, Fry SC, and Nishitani K. (2002). The XTH family of enzymes involved in xyloglucan endotransglucosylation and endohydrolysis: current perspectives and a new unifying nomenclature. Plant Cell Physiol. 2002;43(12):1421-35. DOI:10.1093/pcp/pcf171 |
7. Larsbrink J, Izumi A, Hemsworth GR, Davies GJ, and Brumer H. (2012). Structural enzymology of Cellvibrio japonicus Agd31B protein reveals α-transglucosylase activity in glycoside hydrolase family 31. J Biol Chem. 2012;287(52):43288-99. DOI:10.1074/jbc.M112.416511 |
8. van Hijum SA, Kralj S, Ozimek LK, Dijkhuizen L, and van Geel-Schutten IG. (2006). Structure-function relationships of glucansucrase and fructansucrase enzymes from lactic acid bacteria. Microbiol Mol Biol Rev. 2006;70(1):157-76. DOI:10.1128/MMBR.70.1.157-176.2006 |