Glycosyltransferases

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• Author: Spencer Williams
• Responsible Curator: Spencer Williams

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Overview

Glycosyltransferases are enzymes that catalyze the formation of the glycosidic linkage to form a glycoside. These enzymes utilize 'activated' sugar phosphates as glycosyl donors, and catalyze glycosyl group transfer to a nucleophilic group, usually an alcohol. The product of glycosyl transfer may be an O-, N-, S-, or C-glycoside; the glycoside may be part of a monosaccharide glycoside, oligosaccharide, or polysaccharide ([1, 2, 3, 4, 5]).

Donors

Glycosyltransferases can utilize a range of donor species. Sugar mono- or diphosphonucleotides are sometimes termed Leloir donors (after Nobel prize winner, Luis Leloir); the corresponding enzymes are termed Leloir donors.

Glycosyltransferases that utilize non-nucleotide donors, which may be polyprenol pyrophosphates, polyprenol phosphates, sugar-1-phosphates, or sugar-1-pyrophosphates, are termed non-Leloir glycosyltransferases.

Mechanism

Glycosyltransferases catalyze the transfer of glycosyl groups to a nucleophilic acceptor with either retention or inversion of configuration at the anomeric centre. This allows the classification of glycosyltransferases as either retaining or inverting enzymes.

Inverting glycosyltransferases

Structural and kinetic data for inverting glycosyltransferases support a mechanism that proceeds through a single nucleophilic substitution step, facilitated by an enzymic general base catalyst. The transition state is believed to possess substantial oxocarbenium ion character.

Classification

Sequence based classification

Sequence-based classification uses algorithmic methods to assign sequences to various families. The glycosyltransferases have been classified into more than 90 families [6, 7]; this is permanently available through the Carbohydrate Active enZyme database [8]. Each family (GT family) contains proteins that are related by sequence, and by corollary, fold. This allows several useful predictions to be made since the catalytic machinery is conserved within each family. Usually, the mechanism used (ie retaining or inverting) is conserved within a GT family.

3-D folds

In striking contrast to glycoside hydrolases, which exhibit a wide variety of folds, GTs exhibit a much narrower range of folds.

Leloir GTs

Sugar nucleotide-dependent (Leloir) glycosyltransferases have been found to possess only two different folds, termed the GT-A and GT-B folds [9]. The GT-A fold is typified by the first member to have its X-ray structure determined, SpsA fromBacillus subtilus [10]. The GT-A fold consists of two dissimilar domains, one involved in nucleotide binding and the other binding the acceptor. The GT-B fold was exemplified by its first member, the beta-glucosyltransferase from bacteriophage T4 [11]. The GT-B fold consists of two similar Rossmann fold subdomains.

Example structures

A representative GT-A fold: SpsA from Bacillus subtilus, PDB code 1h7l [10]. The complex also contains two magnesium ions and a molecule of thymidine-5'-diphosphate.

A representative GT-B fold: beta-glucosyltransferase from bacteriophage T4, PDB code 1bgu [11]. The complex also contains a molecule of uridine-5'-diphosphate.

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Non-Leloir GTs

Non-Leloir glycosyltransferases possess other folds. For example the polymerizing glycosyltransferase transglycosylase, which catalyzes the condensation of oligosaccharyl polyprenolphosphate to generate the carbohydrate backbone of peptidoglycan has a bacteriophage-lysozyme-like fold [12]. The Pyrococcus furiosius oligosaccharyltransferase STT3, which catalyzes the transfer of preformed oligosaccharide from a dolichol phosphate glycosyl donor to form asparagine-linked glycoproteins possesses a novel fold [13].

Example structures

Transglycosylase from Staphylococcus aureus, PDB code 2olv [12]. The complex also contains a molecule of the antibiotic moenimycin.	Oligosaccharyltransferase STT3 from Pyrococcus furiosius, PDB code 2zai [13].
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References

2. Lairson LL, Henrissat B, Davies GJ, and Withers SG. (2008). Glycosyltransferases: structures, functions, and mechanisms. Annu Rev Biochem. 2008;77:521-55. DOI:10.1146/annurev.biochem.76.061005.092322 |
3. Coutinho PM, Deleury E, Davies GJ, and Henrissat B. (2003). An evolving hierarchical family classification for glycosyltransferases. J Mol Biol. 2003;328(2):307-17. DOI:10.1016/s0022-2836(03)00307-3 |

   Chapter 5: Coutinho PM, Rancurel C, Stam M, Bernard T, Couto FM, Danchin EGJ, Henrissat B. "Carbohydrate-active Enzymes Database: Principles and Classification of Glycosyltransferases."

4. Campbell JA, Davies GJ, Bulone V, and Henrissat B. (1997). A classification of nucleotide-diphospho-sugar glycosyltransferases based on amino acid sequence similarities. Biochem J. 1997;326 ( Pt 3)(Pt 3):929-39. DOI:10.1042/bj3260929u |
5. Claus-Wilhelm von der Lieth, Thomas Luetteke, and Martin Frank. (2010-01-19) Bioinformatics for Glycobiology and Glycomics: An Introduction. Wiley.

8. Carbohydrate Active Enzymes database; URL http://www.cazy.org/

10. Charnock SJ and Davies GJ. (1999). Structure of the nucleotide-diphospho-sugar transferase, SpsA from Bacillus subtilis, in native and nucleotide-complexed forms. Biochemistry. 1999;38(20):6380-5. DOI:10.1021/bi990270y |
11. Vrielink A, Rüger W, Driessen HP, and Freemont PS. (1994). Crystal structure of the DNA modifying enzyme beta-glucosyltransferase in the presence and absence of the substrate uridine diphosphoglucose. EMBO J. 1994;13(15):3413-22. DOI:10.1002/j.1460-2075.1994.tb06646.x |
12. Lovering AL, de Castro LH, Lim D, and Strynadka NC. (2007). Structural insight into the transglycosylation step of bacterial cell-wall biosynthesis. Science. 2007;315(5817):1402-5. DOI:10.1126/science.1136611 |
13. Igura M, Maita N, Kamishikiryo J, Yamada M, Obita T, Maenaka K, and Kohda D. (2008). Structure-guided identification of a new catalytic motif of oligosaccharyltransferase. EMBO J. 2008;27(1):234-43. DOI:10.1038/sj.emboj.7601940 |
14. Unligil UM and Rini JM. (2000). Glycosyltransferase structure and mechanism. Curr Opin Struct Biol. 2000;10(5):510-7. DOI:10.1016/s0959-440x(00)00124-x |