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The UDP-glucosyltransferase multigene family in insect D2 TRAN Thi Thu Phuong

2013/10/20 22:13 に ユーザー不明 が投稿

2013/10/21

The UDP-glycosyltransferases (UGTs) are a superfamily of enzymes that play a major role in the inactivation and excretion of a great variety of both endogenous and exogenous compounds [1, 2]. These enzymes catalyse the transfer of the glycosyl group from a nucleotide sugar, such as UDP-glucuronic acid, UDP-galactose, UDP-glucose, or UDP-xylose, to a variety of small hydrophobic molecules (aglycones), resulting in more hydrophilic compounds that are efficiently excreted [2]. UGTs are membrane-bound proteins located in the endoplasmic reticulum facing the lumen in animals. The UGT protein structure is divided into two main parts: the N-terminal aglycone substrate binding domain and the C-terminal UDP-glycoside binding domain [3]. Members of this superfamily are present in animals, plants, bacteria, and viruses. The UGTs play an important role in the detoxification of plant allelochemicals encountered by many herbivorous insect in their food. Insects UGT enzymes typically use UDP-glucose as sugar donor [4]. Enzyme activities of the insect UGTs are detected in the fat body, midgut, malpighian tubules, integument, and silk gland consistent with functions in detoxification [3]. However, only limited molecular information is available on insect UDP-glycosyltransferases.

Over 310 putative UGT genes were identified from genomic databases of eight different insect species together with a transcript database from the lepidopteran Helivoverpa armigera [3]. Bombyx mori possesses a largest insect UGT gene family characterized to date, including 45 genes and most of them are clustered on the silkworm chromosomes, with two major clusters on chromosomes 7 and 28, respectively [1, 3]. There are over 30 members of the UGT gene family in the Drosophila genome, scattered throughout chromosomes 2 and 3 [2]. The molecular cloning and functional characterization of a BmUGT1 from the silkworm Bombyx mori [5] and a DmUgt37a1 from Drosophila melanogaster [2] were reported. The complete cDNA clone of Bmugt1 and DmUgt37a1 are 1.6 kb, 1.65 kb, and the predicted protein comprises 520 amino acids, 525 amino acids, respectively, and have about 30% overall amino-acid identity with other members of the UGT family. BmUGT1 had a molecular mass of about 57kDa, while the molecular mass of UGT37a1 was approximately 58kDa. These enzymes catalyse the glucosylation of a range of phenolic and phenol-derived compounds, including flavonoids, coumarins, terpenoids, and simple phenols. Many of the substrates conjugated are plant allelochemicals, suggesting a major role for the enzyme in detoxification responses, for example, flavonoids are plentiful in fruits, vegatables, seeds, and roots [2, 5]. Besides that, in vitro, the fusion protein of B. mori Bm-UGT10286 (UGT86) showed quercetin metabolic activity. The reaction of Ugt86 on the silkworm cocoon pigment quercetin derives from the detoxification of UGTs [6]. These results support a role for the enzyme in detoxication processes, such as minimizing the harmful effects of ingested plant allelochemicals [5].

The potential role of insect phenol β-glucosyltransferases (PGT; EC 2.4.1.35) in detoxifying plant allelochemicals was investigated by studying the ability of these enzymes from a model herbivore, the tobacco hornworm, Manduca sexta, to utilize a variety of plant phenolic as substrates [7]. PGT activity was observed in all tissues in fifth stadium larvae of the tobacco hornworm with highest activities in the labial gland and fat body [8]. Moreover, activities of PGTs in the fat body preparations from the polyphagous grasshopper, Melanoplus sanguinipes, were the highest in tissues of six species of insects [4]. Therefore, herbivores feeding on a wide range of plants may have evolved more active PGTs with wider substrate specificity than those insects adapted to foods containing lower amounts of phenolic defensive chemicals [7].

In conclusion, insect UDP-glycosyltransferases play a pivotal role in the detoxification of plant allelochemicals.  However, they have been studied in only a few insect species. Therefore, further studies need to provide evidences for the biochemical adaptation of herbivorous insects to chemical defences of host plants.

 

REFERENCES

1.   Huang, F. F., Chai, C. L., Zhang, Z., Liu, Z. H., Dai, F. B., Lu, C., Xiang, Z. H., (2008). The UDP-glucosyltransferase multigene family in Bombyx mori. BMC genomics. 9: 563.

2.    Luque, T., O’Reilly D. R., (2002). Functional and phylogenetic analysis of a putative Drosophila melanogaster UDP-glycosyltransferase gene. Insect Biochemistry and Molecular Biology. 32: 1597-1604.

3.     Ahn, S. J., Vogel, H., Heckel, D. G., (2012). Comparative analysis of the UDP-glycosyltransferase multigene family in insects. Insect Biochemistry and Molecular Biology. 42: 133-147.

4.  Ahmad, S. A., Hopkins, T. L., (1993). Phenol β-Glucosyltransferase in six species of insects: properties and tissue localization. Comp. Biochem. Physiol. 104B (3): 515-519.

5.     Luque, T., Okano, K., O’Reilly D. R., (2002). Characterization of a novel silkworm (Bombyx mori) phenol UDP-glucosyltransferase.  Eur. J. Biochem. 269: 819-825.

6.     Xu, X., Wang, M., Wang, Y., Sima, Y., Zhang, D., Li, J., Yin, W., Xu, S., (2013). Green cocoons in silkworm Bombyx mori resulting from the quercetin 5-O-glucosyltransferase of UGT86, is an evolved response to dietary toxins. Mol Biol Rep. 40: 3631-3639.

7. Ahmad, S. A., Hopkins, T. L., (1993). β-Glucosylation of Plant Phenolics by Phenol β-Glucosyltransferase in Larval Tissues of the Tobacco Hornworm, Manduca sexta (L.). Insect Biochem. Molec. Biol. 23 (5): 581-589.

8.     Ahmad, S. A., Hopkins, T. L., (1992). Phenol β-Glucosyltransferase and β-Glucosidase Activities in the Tobacco Hornworm Larva Manduca sexta (L.): Properties and Tissue localization. Archives of Insect Biochemistry and Physiology. 21: 207-224.

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