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

Leloir GTs

Sugar nucleotide-dependent (Leloir) glycosyltransferases have been found to possess only two different folds, termed the GT-A and GT-B folds. The GT-A fold is typified by the first member to have its X-ray structure determined, SpsA fromBacillus subtilus [9]. The GT-B fold was exemplified by its first member, the beta-glucosyltransferase from bacteriophage T4 [10].

Example structures

A representative GT-A fold: SpsA from Bacillus subtilus, PDB code 1h7l [9]. 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 [10]. The complex also contains a molecule of uridine-5'-diphosphate.
<jmol> <jmolApplet> <color>white</color> <frame>true</frame> <uploadedFileContents>1h7l.pdb</uploadedFileContents> <script>cpk off; wireframe off; cartoon; color cartoon powderblue; select ligand; wireframe 0.3; select MG; spacefill;set spin Y 10; spin on; set antialiasDisplay OFF</script> </jmolApplet> </jmol>	<jmol> <jmolApplet> <color>white</color> <frame>true</frame> <uploadedFileContents>1BGU.pdb</uploadedFileContents> <script>cpk off; wireframe off; cartoon; color cartoon powderblue; select ligand; wireframe 0.3; select MG; spacefill;set spin Y 10; spin on; set antialiasDisplay OFF</script> </jmolApplet> </jmol>

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 'lysozyme'-like fold....

Example structures

A representative GT-A fold: SpsA from Bacillus subtilus, PDB code 1h7l [9]. 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 [10].
<jmol> <jmolApplet> <color>white</color> <frame>true</frame> <uploadedFileContents>1h7l.pdb</uploadedFileContents> <script>cpk off; wireframe off; cartoon; color cartoon powderblue; select ligand; wireframe 0.3; select MG; spacefill;set spin Y 10; spin on; set antialiasDisplay OFF</script> </jmolApplet> </jmol>	<jmol> <jmolApplet> <color>white</color> <frame>true</frame> <uploadedFileContents>1BGU.pdb</uploadedFileContents> <script>cpk off; wireframe off; cartoon; color cartoon powderblue; select ligand; wireframe 0.3; select MG; spacefill;set spin Y 10; spin on; set antialiasDisplay OFF</script> </jmolApplet> </jmol>

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References

1. Robert V. Stick and Spencer J. Williams. (2009) Carbohydrates. Elsevier Science.
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/

9. 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 |
10. 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 |