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MetaCyc Enzyme: 3β-hydroxy sterol glucosyltransferase

Gene: SGTL1 Accession Number: G-12498 (MetaCyc)

Synonyms: UDP-glucose:3β-hydroxy sterol glucosyltransferase

Species: Withania somnifera

Summary:
SGTL1 can be classified as a UDP-glucose:sterol-glucosyltransferase based on direct in vitro assays [Sharma07]. Previous experiments had detected this enzymatic activity in Withania somnifera leaf extracts before the gene was cloned [Madina07].

SGTL1 accepts a broad range of sterol substrates and showed the highest activity with dehydroepiandrosterone. But, it also acts with pregnenolone, sitosterol, stigmasterol, deactyl 16-DPA, transandrosterone, 3-β-16,17-α-epoxypregnenolene, brassicasterol, and ergosterol. But, unlike the related SGT from Arabidopsis, SGTL1 does not act on cholesterol or 5-α-cholestan-3β-ol. This indicates that the enzyme has a preference for sterols without a side chain and it also appears to have a higher affinity forr compounds that have a methyl group over an ethyl group at C24 [Sharma07]. SGTL1 did not accept any sugar donors other than UDP-α-D-glucose.

SGTL1 has two putative transmembrane domains, suggesting that it should be membrane-bound, however it might be only loosely associated with membranes as 70% of the activity was detected in the soluble fraction when the enzyme was partially purified from Escherichia coli [Sharma07].

Expression analyses indicate that SGTL1 transcript levels rise in response to salicylate. This may indicate a role for SGTL1 in promoting plant defense. Withania somnifera plants produce a number of specialized secondary metabolites, including steroidal withanolides and glycowithanolides that could potentially be be synthesized with the help of SGTL1. In addition to protecting plants, some of these compunds have proved beneficial for human health [Ichikawa06, Matsuda01].

Unification Links: Entrez-Nucleotide:DQ356887 , NCBI Entrez Protein (GI):86440327 , PlantCyc:MONOMER-16204 , Protein Model Portal:Q2I015 , UniProt:Q2I015

Relationship Links: CAZy:IN-FAMILY:GT1 , InterPro:IN-FAMILY:IPR002213 , InterPro:IN-FAMILY:IPR004276 , Panther:IN-FAMILY:PTHR11926 , Pfam:IN-FAMILY:PF00201 , Pfam:IN-FAMILY:PF03033

Gene-Reaction Schematic: ?

Instance reaction of [UDP-α-D-glucose + a sterol = UDP + an O-glucosylsterol + H+] (2.4.1.173):
i1: UDP-α-D-glucose + solasodine = UDP + solasodine 3-O-β-D-glucopyranoside + H+ (2.4.1.173)

Credits:
Created 04-Feb-2011 by Dreher KA , TAIR


Enzymatic reaction of: β-sitosterol glucosyltransferase (3β-hydroxy sterol glucosyltransferase)

Synonyms: UDP-glucose:β-sitosterol glucosyltransferase

EC Number: 2.4.1.173

UDP-α-D-glucose + sitosterol <=> UDP + 3-O-β-D-glucosyl-β-sitosterol + H+

The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the Enzyme Commission system.

Reversibility of this reaction is unspecified.

Summary:
The Vmax of the reaction using sitosterol is 0.8 pmol mg-1 min-1 and the Vmax / Km is 0.02 [Sharma07].

Kinetic Parameters:

Substrate
Km (μM)
UDP-α-D-glucose
8.0
sitosterol
40.0


Enzymatic reaction of: 3β-hydroxy sterol glucosyltransferase

EC Number: 2.4.1.173

UDP-α-D-glucose + a sterol <=> UDP + an O-glucosylsterol + H+

The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the Enzyme Commission system.

Reversibility of this reaction is unspecified.


Enzymatic reaction of: stigmasterol glucosyltransferase (3β-hydroxy sterol glucosyltransferase)

Synonyms: UDP-glucose:stigmasterol glucosyltransferase

EC Number: 2.4.1.173

UDP-α-D-glucose + stigmasterol <=> UDP + stigmasterol 3-O-β-D-glucoside + H+

The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the Enzyme Commission system.

Reversibility of this reaction is unspecified.

Summary:
The Vmax of the reaction using stigmasterol is 0.6 pmol mg-1 min-1 and the Vmax / Km is 0.02 [Sharma07].

Kinetic Parameters:

Substrate
Km (μM)
Citations
UDP-α-D-glucose
8.0
[Sharma07]
stigmasterol
27.0
[Sharma07]


Enzymatic reaction of: brassicasterol glucosyltransferase (3β-hydroxy sterol glucosyltransferase)

Synonyms: UDP-glucose:brassicasterol glucosyltransferase

EC Number: 2.4.1.173

UDP-α-D-glucose + brassicasterol <=> UDP + 3-O-β-D-glucosyl-brassicasterol + H+

The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the Enzyme Commission system.

Reversibility of this reaction is unspecified.

Summary:
The Vmax of the reaction using brassicasterol is 0.2 pmol mg-1 min-1 and the Vmax / Km is 0.04 [Sharma07].

Kinetic Parameters:

Substrate
Km (μM)
Citations
UDP-α-D-glucose
8.0
[Sharma07]
brassicasterol
4.5
[Sharma07]


Enzymatic reaction of: soladodine glucosyltransferase (3β-hydroxy sterol glucosyltransferase)

Synonyms: UDP-glucose:soladodine glucosyltransferase

EC Number: 2.4.1.173

UDP-α-D-glucose + solasodine <=> UDP + solasodine 3-O-β-D-glucopyranoside + H+

The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the Enzyme Commission system.

Reversibility of this reaction is unspecified.

Summary:
The Vmax of the reaction using solasodine is 0.5 pmol mg-1 min-1 and the Vmax / Km is 0.07 [Sharma07].

Kinetic Parameters:

Substrate
Km (μM)
Citations
UDP-α-D-glucose
8.0
[Sharma07]
solasodine
7.0
[Sharma07]


References

Ichikawa06: Ichikawa H, Takada Y, Shishodia S, Jayaprakasam B, Nair MG, Aggarwal BB (2006). "Withanolides potentiate apoptosis, inhibit invasion, and abolish osteoclastogenesis through suppression of nuclear factor-kappaB (NF-kappaB) activation and NF-kappaB-regulated gene expression." Mol Cancer Ther 5(6);1434-45. PMID: 16818501

Madina07: Madina BR, Sharma LK, Chaturvedi P, Sangwan RS, Tuli R (2007). "Purification and physico-kinetic characterization of 3beta-hydroxy specific sterol glucosyltransferase from Withania somnifera (L) and its stress response." Biochim Biophys Acta 1774(3);392-402. PMID: 17293176

Matsuda01: Matsuda H, Murakami T, Kishi A, Yoshikawa M (2001). "Structures of withanosides I, II, III, IV, V, VI, and VII, new withanolide glycosides, from the roots of Indian Withania somnifera DUNAL. and inhibitory activity for tachyphylaxis to clonidine in isolated guinea-pig ileum." Bioorg Med Chem 9(6);1499-507. PMID: 11408168

Sharma07: Sharma LK, Madina BR, Chaturvedi P, Sangwan RS, Tuli R (2007). "Molecular cloning and characterization of one member of 3beta-hydroxy sterol glucosyltransferase gene family in Withania somnifera." Arch Biochem Biophys 460(1);48-55. PMID: 17324374


Report Errors or Provide Feedback
Please cite the following article in publications resulting from the use of MetaCyc: Caspi et al, Nucleic Acids Research 42:D459-D471 2014
Page generated by SRI International Pathway Tools version 18.5 on Mon Dec 22, 2014, BIOCYC14B.