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(Last
modification: 10. April 2010)
Biphenylsynthase (BIS,
EC 2.3.2.177) aus der Eberesche (Sorbus aucuparia)
(Beerhues et al., 2006;
Liu et
al., 2007)
Sorbus aucuparia
Biphenyle (z.B. Aucuparin) und Dibenzofurane (z.B. Malusfuran) sind Phytoalexine
in ökonomisch wichtigen
Rosaceae, insbesondere in der Subfamilie Maloideae (Kokubun
and Harborne, 1994; Kokubun and
Harborne, 1995; Kokubun et al., 1995); sie
tragen zur Abwehr von Schädlingen bei. Es gab
einen Bericht, dass beide Substanzgruppen nicht gleichzeitig vorkommen (Kokubun and
Harborne, 1995). Experimente mit Zellkulturen von Malus x domestica
(Apfel) zeigten jedoch eine gleichzeitige Induktion von beiden, und die
ähnlichen Substitutionsmuster liessen vermuten, dass Biphenyle die Vorstufen von
Benzofuranen sind (Borejsza-Wysocki
et al., 1999), wie z.B. beim Malusfuran, welches unten gezeigt wird.
Vorstufen-Fütterungs-Versuche (Überblick:
Sultanbawa, 1980)
deuteten darauf hin, dass die Schlüsselreaktion der Biosynthese durch eine PKS
durchgeführt wurde, mit Benzoyl-CoA als Starter, drei Kondensationsreaktionen
mit Malonyl-CoA, gefolgt von einer Stilbensynthase (STS) Typ Ringfaltung (Schröder, 2000).
Sorbus aucuparia
(mountain ash, Eberesche, Vogelbeere:
Baum des Jahres 1997!)
und seine Zellkulturen sind interessante Systeme zum Studium der postulierten
Polyketidsynthase (PKS). Wikipedia enthält eine ziemlich gute Seite auf Deutsch
(Vogelbeere),
aber die englische Seite (Sorbus_aucuparia)
lässt sehr zu wünschen übrig. Jedoch nicht einmal die deutsche Seite erwähnt die
Biphenyl-Phytoalexine, die uns hier interessieren. Genauso wenig wird
Parasorbosid erwähnt, die bittere Geschmackskomponente in den Ebereschenbeeren:
Das Grundgerüst wird auch über eine Typ III PKS synthetisiert, aber mit nur zwei
Kondensationsreaktionen und Acetyl-CoA als Starter-Substrat: Mehr....
Die Biphenylsynthase (BIS) Aktivität wurde mit
Extrakten aus Zellkulturen nachgewiesen, die durch Behandlung mit Hefeextrakt
induziert waren (Liu et al.,
2004), und die gleiche Gruppe klonierte auch die cDNA (Liu
et al., 2007). Das Protein zeigte etwa 60% Identität mit anderen Mitgliedern
der Typ III PKS. Eine phylogenetische
Analyse zeigte, dass es die engste Verwandtschaft mit der Benzophenonsynthase
(BPS) hat, also einem Enzym, welches auch Benzoyl-CoA als Starter verwendet,
aber eine CHS-Typ Ringfaltung durchführt:
Mehr....
Angemerkt werden soll, dass die BIS keine Aktivität mit
4-Coumaroyl-CoA hat, also Resveratrol nicht synthetisieren kann.
Eine andere interessante Frage ist, ob die BIS den
gleichen
Aldolschalter-Mechanismus, der bei der STS aus der Kiefer identifiziert
wurde (Pinus sylvestris) (Austin
et al., 2004). Das scheint aber nicht der Fall zu sein, denn die
Aminosäuren typisch für den Aldolschalter sind anscheinend nicht in der BIS zu
finden. Es könnte deshalb sein, dass es noch andere Mechanismen für die STS-Typ
Ringfaltung gibt (Mehr...).
Update
06.October 2009:
Eine neuere
Publikation beschrieb die Klonierung von zwei zusätzlichen BIS cDNAs, und
eine zusätzliche Charakterisierung der Reaktionen der BIS-Proteine mit
2-Hydroxybenzoyl-CoA: Die Synthese von 4-Hydroxycoumarin durch diese Typ III
PKS: Mehr...
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Zitate
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Liu, B., Raeth, T., Beuerle,
T., Beerhues, L., 2007. Biphenyl synthase, a novel type III polyketide
synthase. Planta 225, 1495-1503.
Biphenyls and dibenzofurans are the phytoalexins of the Maloideae, a
subfamily of the economically important Rosaceae. The carbon skeleton of
the two classes of antimicrobial secondary metabolites is formed by
biphenyl synthase (BIS). A cDNA encoding this key enzyme was cloned from
yeast-extract-treated cell cultures of Sorbus aucuparia. BIS is a
novel type III polyketide synthase (PKS) that shares about 60% amino
acid sequence identity with other members of the enzyme superfamily. Its
preferred starter substrate is benzoyl-CoA that undergoes iterative
condensation with three molecules of malonyl-CoA to give
3,5-dihydroxybiphenyl via intramolecular aldol condensation. BIS did not
accept CoA-linked cinnamic acids such as 4-coumaroyl-CoA. This substrate,
however, was the preferential starter molecule for chalcone synthase (CHS)
that was also cloned from S. aucuparia cell cultures. While BIS
expression was rapidly, strongly and transiently induced by yeast
extract treatment, CHS expression was not. In a phylogenetic tree, BIS
grouped together closely with benzophenone synthase (BPS) that also uses
benzoyl-CoA as starter molecule but cyclizes the common intermediate via
intramolecular Claisen condensation. The molecular characterization of
BIS thus contributes to the understanding of the functional diversity
and evolution of type III PKSs.
Zurück zum Text
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Liu, B., Beuerle, T., Klundt,
T., Beerhues, L., 2004. Biphenyl synthase from yeast-extract-treated cell
cultures of Sorbus aucuparia. Planta 218, 492-496.
Biphenyls and dibenzofurans are the phytoalexins of the Maloideae, a
subfamily of the economically important Rosaceae. The biphenyl aucuparin
accumulated in Sorbus aucuparia L. cell cultures in response to
yeast extract treatment. Incubation of cell-free extracts from
challenged cell cultures with benzoyl-CoA and malonyl-CoA led to the
formation of 3,5-dihydroxybiphenyl. This reaction was catalysed by a
novel polyketide synthase, which will be named biphenyl synthase. The
most efficient starter substrate for the enzyme was benzoyl-CoA.
Relatively high activity was also observed with 2-hydroxybenzoyl-CoA but,
instead of the corresponding biphenyl, the derailment product
2-hydroxybenzoyltriacetic acid lactone was formed.
Zurück zum Text
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Beerhues, L., Liu, B.,
Raeth, T., Klundt, T., Beuerle, T., Bocola, M., 2006.
Benzoic acid-specific type III polyketide synthases. In: Rimando, A. M.,
Baerson, S. R. (Eds.), Polyketides: Biosynthesis, Biological Activities and
Genetic Engineering, American Chemical Society, Washington, D.C., pp.
97-108.
Benzophenone
synthase (BPS) and biphenyl synthase (BIS) catalyze the formation of
the same linear tetraketide from benzoyl-CoA and three molecules of
malonyl-CoA. However, BPS cyclizes this intermediate via intramolecular
C6-C1 Claisen condensation, whereas BIS uses intramolecular C2-C7 aldol
condensation. Benzophenone derivatives include polyprenylated polycyclic
compounds with high pharmaceutical potential. Biphenyl derivatives are
the phytoalexins of the economically important Maloideae.
Zurück zum Seitenanfang
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Austin, M. B., Bowman, M.
E., Ferrer, J.-L., Schröder, J., Noel, J. P., 2004. An aldol switch
discovered in stilbene synthases mediates cyclization specificity of type
III polyketide synthases. Chemistry & Biology 11, 1179-1194.
Stilbene synthase (STS) and chalcone synthase (CHS) each catalyze the
formation of a tetraketide intermediate from a CoA-tethered phenylpropanoid
starter and three molecules of malonyl-CoA, but use different cyclization
mechanisms to produce distinct chemical scaffolds for a variety of plant
natural products. Here we present the first STS crystal structure, and
identify, by mutagenic conversion of alfalfa CHS into a functional stilbene
synthase, the structural basis for the evolution of STS cyclization
specificity in type III polyketide synthase (PKS) enzymes. Additional
mutagenesis and enzymatic characterization confirms that electronic effects
rather than steric factors balance competing cyclization specificities in CHS
and STS. Finally, we discuss the problematic in vitro reconstitution of
plant stilbenecarboxylate pathways, using insights from existing biomimetic
polyketide cyclization studies to generate a novel mechanistic hypothesis to
explain stilbenecarboxylate biosynthesis.
Sonderdruckanfrage
Zurück zum Text
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Borejsza-Wysocki,
W., Lester, C., Attygalle, A. B., Hrazdina, G., 1999. Elicited cell
suspension cultures of apple (Malus x domestica) cv. Liberty produce
biphenyl phytoalexins. Phytochemistry 50, 231-235.
Yeast extract treated cell suspension cultures from a scab (Venturia
inaequalis) resistant apple cultivar, Malus x domestica
cv. Liberty produce dibenzofuran and biphenyl compounds as part of
their defense system against fungal invasion. We have isolated and
identified three biphenyl derivatives, 4-hydroxy-3,5- dimethoxybiphenyl
(aucuparin), 2',4,-dihydroxy-3,5- dimethoxybiphenyl
(2'-hydroxy-aucuparin) and 2'-O-beta-D-
glucopyranosyl-4-hydroxy-3,5-methoxybiphenyl (2'-o-beta-D-
glucopyranosylaucuparin) from the cells and the medium and show here
their chemical properties. Although this is the first identification of
2'-glucopyranosylaucuparin, its aglycone, 2'- hydroxyaucuparin and
aucuparin have been reported previously [Kokubun, T., Harborne, J.B.,
Phytochemistry, 1995, 40, 1649- 1654.] from fungus infected wood of
Malus species. Production of an array of dibenzofuran and biphenyl
derivatives in response to fungal attack may he an important part of the
disease resistance mechanism of scab resistant apple cultivars.
Zurück zum Text
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Kokubun, T., Harborne, J.
B., 1994. A survey of phytoalexin induction in leaves of the Rosaceae by
copper ions. Zeitschrift für Naturforschung 49c, 628-634.
The
leaves of 130 species of Rosaceae were surveyed for phytoalexin
induction. Both biotic and abiotic induction was examined and antifungal
compounds were detected in 47 species. However, these compounds appeared
to be constitutive metabolites, released from bound phenolic materials
already present in the leaf. In Pyrus, hydroquinone was produced from
the hydrolysis of arbutin present in the vacuole before inoculation. In
most other species, the fungitoxic agents were mainly catechin-like
derivatives, apparently released from the tannins present within the
leaf. By contrast, the synthesis in the leaf of the characteristic
biphenyl or benzofuran phytoalexins which are produced in sapwood, was
confined to a very few species. The biphenyl aucuparin was identified as
a phytoalexin from the leaves of Sorbus aucuparia.
Zurück zum Text
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Kokubun, T., Harborne, J.
B., 1995. Phytoalexin induction in the sapwood of plants of the Maloideae
(Rosaceae): biphenyls or dibenzofurans. Phytochemistry 40, 1649-1654.
Following fungal inoculation or natural infection, five biphenyl
phytoalexins (aucuparin and its 2' and 4' oxygenated derivatives) were
induced variously in the sapwood of Aronia, Chaenomeles, Eriobotrya,
Malus (three spp.) and of Sorbus aucuparia. By contrast, 14 dibenzofuran
phytoalexins were induced variously in sapwood of Cotoneaster (7 spp.),
Crateagus, Cydonia, Mespilus, Photinia, Pseudocydonia, Pyracantha, Pyrus
and two Sorbus spp. (S. chamaemespilum and S. domestica). These were
five cotonefurans, three eriobofurans, five pyrufurans and a 2,3,4,7,8-
pentaoxygenated dibenzofuran trimethyl ether. No plant has yet been
found to produce both types of phytoalexin, although o-hydroxybiphenyls
are theoretically precursors of the dibenzofurans. The ability to
synthesize either biphenyls or dibenzofurans appears to be
genus-specific, except in the case of Sorbus. In 18 of the 38 species
tested, these phytoalexins were accompanied by constitutive antifungal
phenolics, most of which appeared to be released from bound (glycosidic)
forms during the infection process. These were identified variously as
hydroquinone, p-hydroxyacetophenone, acetovanillone,
5,7-dihydroxychromone, chrysin, sakuranetin and naringenin. Woody
members of the subfamilies Prunoideae and Spiraeoideae failed to yield
any phytoalexins on induction, but did contain constitutive antifungal
compounds. The limited frequency of the phytoalexin response within the
family as a whole is considered in relation to the accumulation of
constitutive antifungal agents in these plants.
Zurück zum Text
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Kokubun, T., Harborne, J.
B., Eagles, J., Waterman, P. G., 1995. Antifungal biphenyl compounds are
the phytoalexins of the sapwood of Sorbus aucuparia.
Phytochemistry 40, 57-59.
An
examination of the sapwood tissue of Sorbus aucuparia L. has
revealed that aucuparin and its derivatives are essentially
absent from healthy tissue, and are only produced as phytoalexins
following fungal infection. Five biphenyls were identified: aucuparin,
2'-methoxyaucuparin, 4'-methoxyaucuparin, 2'- hydroxyaucuparin and
isoaucuparin (2'-hydroxy-3,5- dimethoxybiphenyl). The latter is a new
phytoalexin. A survey of 11 individual Sorbus trees showed that not all
these compounds are necessarily produced in the phytoalexin response.
Zurück zum Text
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Schröder, J., 2000. The
family of chalcone synthase-related proteins: functional diversity and
evolution. Recent Advances in Phytochemistry 34, 55-89.
CONCLUSIONS: Results in the last few years showed that the
well-known chalcone synthase (CHS) is only one example from a family of
plant polyketide synthases. Other members of the family which are
identified by function and sequences are the stilbene synthases (STS),
acridone synthase (ACS), and a pyrone synthase (2PS); all of these
proteins share about 65-70% identity with CHS. The properties of several
other enzymes suggest that they are members of the protein family, and
precursor feeding studies suggest that the number may be much larger
than suspected so far. The diversity of functions is based on different
substrate specificities, variations in the number of condensation
reactions, folding of intermediates to different products, and
modification of intermediates by other enzymes.
The recently published first crystal structure of a CHS raises hopes
that it will be possible to understand at the protein sequence level the
programming of the proteins for the various functions; this then will
facilitate the design of enzymes synthesizing new products.
The understanding of the evolution of the protein family is still
rudimentary. The available data suggest that the functional diversity
known in present-day plants could be the results of fairly recent
developments from CHS by gene duplication and mutation. The presence of
CHS-related sequences in bacteria indicates that the basic function unit
predated the evolution of plants. The recent functional identification
of such a protein from Streptomyces griseus suggests that
the functional diversity in bacteria may even be larger than in plants.
Zurück zum Text
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Sultanbawa, M. U. S.,
1980. Xanthonoids of tropical plants.
Tetrahedron 36,
1465-1506.
No Abstract available.
Zurück zum Text
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