Aristolochene synthase

OCTOPINE DEHYDROGENASE ARGININOSUCCINATE LYASE ARGININOSUCCINATE SYNTHETASE ARISTOLOCHENE SYNTHASE Arogenate dehydrogenase,... 

The 5-epi-aristoIochene synthase of tobacco makes the 5-epimer of aristolochene (Fig. 22-4). It binds the diphosphate group within a central cavity using two Mg2+ ions held by carboxylates, some of which are in the DDXXD sequence found also in polyprenyl diphosphate synthases. The enzyme active sites of both the epi-aristolochene synthase and a pentale-nene synthase from Streptomyces96 are rich in polar groups that form hydrogen-bonded networks and which participate in proton abstraction and donation during the rearrangement reactions that must occur. 

The formation of the sesquiterpene (+)-5-epi-aristolochene (2) represents, from a biosynthetic point of view, the transformation requiring the fewest steps among those discussed in this review. A single enzyme, tobacco 5-epi-aristolochene synthase (TEAS), converts the biosynthetic precursor, farnesyl diphosphate (6), to... 

Figure 10.11 A proposed pathway for the biosynthesis of capsidiol in elicitor-treated tobacco cell cultures. Earlier work had not resolved how 5-epi-aristolochene, synthesized from FPP by the action of 5-epi-aristolochene synthase, was converted to capsidiol.

CANE, D. E., TSANTRIZOS, Y. S., Aristolochene synthase. Elucidation of the cryptic germacrene A synthase activity using the anomalous substrate dihydrofamesyl diphosphate, J. Amer. Chem. Soc., 1996,118,10037-10040. 

CANE, D. E., KANG, I., Aristolochene synthase purification, molecular cloning, high-level expression in Escherichia coli, and characterization of the Aspergillus terreus cyclase, Arch. Biochem. Biophys., 2000,376,354-364. 

CARUTHERS, J. M., KANG, I., RYNKIEWICZ, M. J., CANE, D. E., CHRISTIANSON, D. W., Crystal structure determination of aristolochene synthase from the blue cheese mold, Penicillium roqueforti, J. Biol. Chem., 2000, 275, 25533-25539. 

STARKS, C. M., BACK, K. W., CHAPPELL, J., NOEL, J. P, Structural basis for cyclic terpene biosynthesis by tobacco 5- epi-aristolochene synthase, Science, 1997, 111, 1815-1820. 

Cane, D.E., and Bryant, C. (1994). Aristolochene synthase. Mechanism-based inhibition of a terpenoid cyclase. J Am Chem Soc 116 12063-12064. 

The recently published crystal structure of tobacco epi-aristolochene synthase (a sesquiterpene synthase) has provided the first look at the three-dimensional configuration of a plant terpene s)mthase (Starks et al, 1997). 

Direct-defense compounds can be either constitutively present in (specific parts of) the plant or be produced after induction by pathogens or herbivores. The latter compound will be less costly for the plant. For example, elicitor-induced accumulation of the antimicrobial sesquiterpenoid capsidiol correlated with the induction of 5-ept-aristolochene synthase, which is a branch-point sesquiterpene cyclase involved in the synthesis of sesquiterpene phytoalexins (8). In rice Oryza saliva L.), 14 diterpenoid phytoalexins have been identified. All these compounds are accumulated in rice leaves after inoculation with the... 

The three-dimensional structures of three non-plant sesquiterpene synthases reveals a single domain composed entirely of a-hehces and loops despite the low homology on amino acid sequence level [14,16,17]. The secondary elements of 5-epi-aristolochene synthase, a plant sesquiterpene synthase, conform to this pattern with the exception of two domains solely composed of a-helices and loops. It is reasonable, but still a matter of debate, to extrapolate these data to the case of amorpha-4,11-diene synthase, which will probably only display a-hehces and loops once the crystal structme has been solved. 

A further element shared by all sesquiterpene synthases is the need for a divalent metal ion as cofactor. The metal ion is essential for substrate binding but also for product specificity. The metal ions stabihze the negatively charged pyrophosphate group of farnesyl diphosphate as illustrated by the crystal structure of 5-epz-aristolochene synthase [9]. The highly conserved sequence (I, L, V)DDxxD(E) serves to bind the metal ions in all known terpene and prenyl synthases (Fig. 5) [18-22]. A further interesting property among terpene synthases is that the active sites are enriched in relatively inert amino acids, thus it is the shape and dynamic of the active site that determines catalytic specificity [23]. 

Picaud et al. purified recombinant AMDS and determined its pH optimum to 6.5 [24]. Several sesquiterpene synthases show maximum activity in this range examples are tobacco 5-epz-aristolochene synthase [25,26], germa-crene A synthase from chickory [26] and nerolidol synthase from maize [27]. Terpenoid synthases are, however, not restricted to a pH optimum in this range. Intriguing examples are the two (-l-)-(5-cadinene synthase variants from cotton, which exhibit maximum activity at pH 8.7 and 7-7.5, respectively [28] and 8-epi-cedrol synthase from A. annua [29] with the pH optimum around... 

Stabilisation of transition states prior to and following eudesmane cation in aristolochene synthase, S. Forcat and R.K. Allemann, Org. Biomol. Chem., 2006, 4, 2563. 

Nt-EAS Nicotiana tabacum 5-epi-aristolochene synthase tps terpene synthase... 

Tertiary Structure of 5-ep/-Aristolochene Synthase and Prediction of Structure/Function Relationships... 

Because of the striking similarities in properties, mechanisms and primary structures between the plant monoterpene, sesquiterpene, and diterpene synthases [21], the recent crystallization and X-ray diffraction analysis of 5-epi-aristolochene synthase (Nt-EAS) [62] is of central importance in providing the first three-dimensional model with which fundamental and common structural themes may be proposed. This model provides a convenient starting point for discussing general structure/function relationships of all terpene cyclases. 

Neither capsidiol nor glutinosone could be detected in healthy tissues. According to Bohlmann et al. (2002) . it is conceivable that capsidiol contributes not only to an inducible defense against pathogens, but also to a constitutive defense in an organ-specific manner in some species of Nicotiana Constitutive expression of 5-epi-aristolochene synthase (EAS) and capsidiol accumulation could not be observed in shoots of N. attenuata, but enzyme transcripts were induced by feeding of Manduca sexta, the tobacco homworm. However, EAS was expressed constitutively in roots of this N. species and N. sylvestris Spec. Comes. 

Bohlmann J, Stauber EJ, Krock B, Oldham NJ, Gershenzon J, Baldwin IT (2002) Gene expression of 5-e/7/-aristolochene synthase and formation of capsidiol in roots of Nicotiana attenuata and N. sylvestris. Phytochemistry 60 109-116... 

O Maille, RE. et al. (2006) Biosynthetic potential of sesquiterpene synthases alternative products of tobacco 5-epi-aristolochene synthase. Arch. Biochem. Biophys. 448, 73-82... 

FIGURE 7.4 Crystal structure of (a) bisabolene synthase active center bound to farnesyl diphosphate inhibitor (b) aristolochene synthase cocrystallized with FDP (metal coordination and hydrogen bonds are shown as dashed lines magnesium anions and water molecules are shown as spheres) and the proposed catalytic mechanisms for each cyclization Images created with PyMOL. (See insert for color representation of the figure.)... 

---