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Structures of the UDP glycosyltransferase of GT1 family, D2, Tran Thi Thu Phuong

2013/11/26 17:53 に ユーザー不明 が投稿
2013/11/25

Glycosyltransferases (GTs) are very ancient enzyme family that catalyses the synthesis of glycosidic linkages by the transfer of a sugar residue from a donor to an acceptor. The majority of GTs utilize nucleotide-sugars as donors, such as UDP-glucuronic acid, UDP galactose, UDP glucose, or UDP xylose. In March 2012, the database contained about 87,000 GT entries divided into over 90 families, the vast majority of these sequences being uncharacterized open-reading frames. To date, X-ray crystal structures are available for over 100 GTs in 38 GT families. Surprisingly, conserved three-dimensional architecture has been seen for the structures of all nucleotide sugar dependent GTs to date, since they exhibit only two types of fold (and variants thereof), termed GT-A and GT-B [1]. GT-A enzymes are generally metal dependent with a characteristic DxD motif and consist of two closely linked α/β/α Rossmann nucleotide binding domains. GT-B enzymes are metal independent and consist of two α/β/α domains separated by a flexible linker region and interdomain cleft [1, 2]. In this seminar, I will focus on the structure of several UGT enzymes, which are predicted to adopt a GT-B fold.

Invertebrates and plants UDP-glycosyltransferases (UGTs) do contain GT-B fold with a N-terminal domain primarily involved in acceptor binding and a C-terminal domain that binds the nucleotide sugar donor [3]. UGTs have highly similar C-terminal domains and highly variable N-terminal domains, thereby imparting to each enzyme a distinct, but often overlapping set of substrate specificities crystal [2]. UGTs are abundant in all insect species; for example, the silkworm Bombyx mori alone has 42 predicted UGTs that can be divided into 5 groups [3]. In the silkworm Bombyx mori, dietary flavonoids are metabolized and accumulate in cocoons, thereby causing green coloration. BmUGT86 is responsible for green b locus involving the green cocoon, and BmUGT86 is virtually the sole source of UGT activity toward the 5-O position of quercetin, one of flavonoids derived from mulberry leaves. The structure of genomic of BmUGT86 is similarities with other UGTs within the region responsible for green b and coding sequences (64-80% amino acid identity) [4].

Crystal structures of several flavonoids GTs from plants, such as UGT78G1 [5], UGT71G1 [6], UGT85H2 [7], and VvGT1 [8], which are important for the glycosylation of secondary metabolites, were solved in recent years. The overall structure of these enzymes consists of two N- and C-terminal domains with similar Rossmann-type folds. The N-terminal domain contains seven-stranded parallel β sheet flanked by eight or nine α helices. The C-terminal domain contains a six stranded β sheet flanked by eight α helices. The two domains pack very tightly and form a deep cleft that is the binding site for substrates. The final C-terminal helix crosses from the C-terminal domain to complete the N-terminal domain fold. These three-dimensional structures share high levels of similarity, although the amino acid sequence identity is only about 20%. Moreover, UGT71G1, UGT85H2, and VvGT1 all recognize multiple acceptors, including the common acceptor quercetin. Therefore, enzyme structural similarity is consistent with the similarity of substrate binding and product regioselectivity [6, 7].

In contrast to plant UGTs, until recently, a full length mammalian UGT crystal structure is not available. The 1.8-Å resolution X-ray crystal structure of the C-terminal domain of human UGT2B7 is the only crystal structure of a mammalian UGT target determined to date [2, 9]. Nevertheless, the crystal of the C-terminus of UGT2B7 and crystals of several distantly-related plant and bacterial UGTs have provided structural information to help guide the generation of 3D homology models of the entire mammalian UGT protein. These homology models have proved useful in elucidating the relationship between primary amino acid sequence and aglycone and UDP-sugar selectivity.

In conclusion, family 1 GT enzymes, the UDP glycosyltransferases, play central roles in the metabolism and detoxification of foreign chemicals. UGT enzymes have highly similar C-terminal domains and highly variable N-terminal domain. These structures provide essential insights into the enzyme catalytic mechanism and specificity of sugar donors and acceptors.

 

REFERENCES

1. Breton, C., Fournel-Gigleux, S., Palcic, M. M., (2012). Recent structures, evolution and mechanisms of glycosyltransferases. Current Opinion in Structural Biology. 22:540-549.

2. Miley, M. J., Zielinska, A. K., Keenan, J. E., Bratton, S. M., Radominska-Pandya, A., Redinbo, M. R., (2007). Crystal structure of the cofactor-binding domain of the human phase II drug-metabolism enzyme UDP-glucuronosyltransferase 2B7. J. Mol. Biol. 369: 498-511.

3. Meech, R., Miners, J. O., Lewis, B. C., Mackenzie, P, I., (2012). The glycosidation of xenobiotics and endogenous compounds: Versatility and redundancy in the UDP glycosyltransferease superfamily. Pharmacology& Therapeutics.134: 200-218.

4. Daimon, T., Hirayama, C., Kanai, M., Ruike, Y., Meng, Y., Kosegawa, E., Nakamura, M., Tsujimoto, G., Katsuma, S., Shimada, T., (2010). The silkworm Green b locus encodes a quercetin 5-O-glucosyltransferase that produces green cocoons with UV-shielding properties. PNAS. 107 (25): 11471-11476.

5. Modolo, L. V., Li, L., Pan, H., Blount, J. W., Dixon, R. A., Wang, X., (2009). Crystal structures of glycosyltransferase UGT78G1 reveal the molecular basis for glycosylation and deglycosylation of (Iso) flavonoids. J. Mol. Biol. 392: 1292-1302.

6. Shao, H., He, X., Achnine, L., Blount, J. W., Dixon, R. A., Wang, X., (2005). Crystal Structures of a multifunctional triterpene/flavonoid glycosyltransferase from Medicago truncatula. The plant cell. 17: 3141-3154.

7. Li, L., Modolo, L. V., Achnine, L. L. E.-T. L., Dixon R. A., Wang, X., (2007). Crystal structure of Medicago truncatula UGT85H2 - insights into the structural basis of a multifunctional (Iso) flavonoid glycosyltransferase. J. Mol. Biol. 370: 951–963.

8. Offen W., Martinez-Fleites, C., Yang, M., Kiat-Lim, E., Davis, B. G., Tarling, C. A., Ford, C. M., Bowles, D. J., Davies, G. J., (2006). Structure of a flavonoid glucosyltransferase reveals the basis for plant natural product modification. The EMBO journal. 25: 1396-1405.

9. Radominska-Pandya1, A., Bratton, S. M., Redinbo, M. R., Miley, M. J., (2010). The crystal structure of human UDP-glucuronosyltransferase 2B7 C-terminal end is the first mammalian UGT target to be revealed: the significance for human UGTs from both the 1A and 2B families. Drug Metabolism Reviews, 42(1): 133-144.


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