Oxoglutarate-dependent Dioxygenases

Prolyl 4-hydroxylation is the most abundant posttranslational modification of collagens. 4-Hydroxylation of proline residues increases the stability of the triple helix and is a key element in the folding of the collagen triple helix. " In vertebrates, almost all the Yaa position prolines of the Gly-Xaa-Yaa repeat are modified to 4(I( )-hydroxylproline by the enzyme P4H (EC 1.14.11.2), a member of Fe(II)- and 2-oxoglutarate-dependent dioxygenases. This enzyme is an 0 2/ b2-type heterotetramer in which the / subunit is PDI (EC 5.3.4.1), which is a ubiquitous disulfide bond catalyst. The P4H a subunit needs the 13 subunit for solubility however, the 13 subunit, PDI, is soluble by itself and is present in excess in the ER. Three isoforms of the a subunit have been identified and shown to combine with PDI to form [a(I)]2/ 2) [< (II)]2/32> or [a(III)]2/32 tetramers, called the type... 

Fig. 6.2 The flavonoid core biosynthetic pathway. The P450s and 2-oxoglutarate-dependent dioxygenases (2-ODDs) are indicated by underlined and bolded titles, respectively. F3 H and F3 5 H are capable of using flavanones (2-3 = single bond, R1 = H), flavones (2-3 = double bond, R1 = H), dihydroflavonols (2-3 = single bond, R1 = OH), or flavonols (2-3 = double bond, R1 = OH) for a substrate. FNS activity has been indicated with two different enzymes, FNS-11 (P450) and the less-common FNS-I (2-ODD)...

Flavone synthase (FNS EC 1.14.11.22) introduces a double bond between C2 and C3 of a flavanone to produce the corresponding flavone. This activity was initially identified in parsley cell suspension cultures and subsequently shown to be encoded by a 2-oxoglutarate-dependent dioxygenase [67, 78, 79], This enzyme, now known as FNS-I, appears to have very limited distribution. To date, it has only been identified in the Apiaceae family (Umbellifers). The more widely occurring FNS-II (CYP93B) was initially identified from snapdragon (Antirrhinum majus) flowers [80] and was subsequently shown to be a P450 enzyme. FNS-I, FNS-II, and the various roles flavones play in plant species have recently been reviewed by Martens and Mithofer [81], Subsequent to this review, Yu et al. [82] demonstrated that the characteristic lack of natural accumulation of flavones in Brassicaceae could not be overcome in A. thaliana even by overexpression of recombinant parsley FNS-I. 

Halbwirth H, Fischer TC, Schlangen K, Rademacher W, Schleifer K, Forkmann G, Stitch K (2006) Screening for inhibitors of 2-oxoglutarate-dependent dioxygenases flavanone 3-hydroxylase and flavonol synthase. Plant Sd 171 194-205... 

Martens S, Forkmann G, Britsch L, WeUmann F, Matem U, Lukacin R (2003) Divergent evolution of flavonoid 2-oxoglutarate-dependent dioxygenases in parsley. FEBS Lett 544 (l-3) 93-98... 

Matsuda, J. et al.. Molecular cloning of hyoscyamine 6p-hydroxylase, a 2-oxoglutarate-dependent dioxygenase, from cultured roots of Hyoscyamus niger. J. Biol Chem., 266, 9460, 1991. 

Anzelotti, D. and Ibrahim, R.K., Novel flavonol 2-oxoglutarate dependent dioxygenase affinity purification, characterization, and kinetic properties. Arch. Biochem. Biophys., 382, 161, 2000. 

Roemmelt, S. et al., Formation of novel flavonoids in apple (Malus x domesticd) treated with the 2-oxoglutarate-dependent dioxygenase inhibitor prohexadione-Ca, Phytochemistry, 64, 709, 2003. 

In plants accumulating anthocyanins, flavonols, and proanthocyanidins, naringenin is stereospecifically hydroxylated at position 3 of the C-ring (C3) by the 2-oxoglutarate-dependent dioxygenase flavanone 3-hydroxylase (F3H, EC 1.14.11.9) to yield the 3-hydroxy-trans-flavanone (syn. dihydroflavonol) dihy-drokaempferol [Springob et al., 2003] (Fig.21 2). Dihydroquercetin (3, 4, 5,5, 7-... 

The branch pathway for anthocyanin biosynthesis starts with the enzymatic reduction of dihydrofiavonols to their corresponding flavan 3,4-diols (leucoanthocyanidins) by substrate-specific dihydroflavonol 4-reductases (DFR). Flavan 3,4-diols are the immediate precursors for the synthesis of catechins and proanthocyanidins. Catechins are formed by enzymatic reduction of the flavan 3,4-diols in the presence of NADPH to leucoanthocyanidins, which are subsequently converted to anthocyanidins by the 2-oxoglutarate-dependant dioxygenase, anthocyanidin synthase. Further glycosylation, methylation, and/or acylation of the latter lead to the formation of the more stable, colored anthocyanins (Scheme 1.1). The details of the individual steps involved in flavonoid and isoflavonoid biosynthesis, including the biochemistry and molecular biology of the enzymes involved, have recently appeared in two excellent reviews.7,8... 

DE CAROLIS, E., DE LUCA, V., 2-Oxoglutarate-dependent dioxygenases and related enzymes Biochemical characterization. Phytochemistry, 1994, 36, 1094-1107. 

KLIEBENSTEIN, D.J., LAMBR1X, V.M., REICHELT, M., GERSHENZON, J., MITCHELL-OLDS, T., Gene duplication in the diversification of secondary metabolism Tandem 2-oxoglutarate-dependent dioxygenases control glucosinolate biosynthesis in Arabidopsis., Plant Cell, 2001,13,681-693. 

VAZQUEZ-FLOTA, F.A., DE CAROLIS, E., ALARCO, A.M., DE LUCA, V., Molecular cloning and characterization of deacetoxyvindoline 4-hydroxylase, a 2-oxoglutarate dependent dioxygenase involved in the biosynthesis of vindoline in Catharanthus roseus (L.) G. Don. Plant Mol. Biol., 1997,34,935-948. 

The enzyme that catalyzes this reaction, lysine hydroxylase, is, like prolyl hydroxylase, a Fe(II)/2-oxoglutarate dependent dioxygenase but exhibits a distinct substrate specificity. 

Figure 5.8 Examples of oxidative secondary transformations in terpenoid biosynthesis, (a) Hydroxylation of epi-aristolochene at the 3-position by a cytochrome P450-dependent terpene hydroxylase in Capsicum annuum (Hoshino et ai, 1995). (b) Conversion of GA12 to CA9 by a 2-oxoglutarate-dependent dioxygenase involved in gibberellin biosynthesis.

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