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(Last modification:
10. April 2010)
'Orphan' PKS in
Physcomitrella patens:
Alkylpyrones and
Alkylresorcinols
An interesting case has been
described for the moss
Physcomitrella patens (Wikipedia:
English;
German = Kleines Blasenmützenmoos, a really funny name!) which has been used
as a model organism for evolution. It also is one of the few known multicellular
organisms with highly efficient homologous recombination, and this makes the
moss an interesting experimental system for many questions. The
genome is also being sequenced at
present.
With regard to type III
PKS, it is interesting that it does not only contain the expected group of chalcone
synthases (CHS) (Jiang et al., 2006), but
also a gene for another type III protein that is only distantly related to
typical CHS. The protein is also in
the relationship tree shown in this website;
for this purpose it is named ARS P. patens (alkylresorcinol
synthase, see below). It is also noteworthy that the ARS belongs to a rather large subbranch of
proteins which are clearly far away from most other type III PKS. In this group
only the two proteins from A. thaliana were functionally characterized:
most interestingly, the recombinant enzyme synthesized long-chain alkylpyrones
in vitro: more...!
So far the information on the Physcomitrella protein is
confined to a database entry, a review article and a personal communication by
Prof.
PpCHS11
in Jiang et al., 2006) condenses long-chain acyl-CoA ester with malonyl-CoA to
produce alkylpyrones and pentaketide alkylresorcinols, depending on the starter
unit. For simplification, I therefore called it an alkylresorcinol synthase
(ARS) in the relationship tree, although this may be only one of the functions:
e seems no clear-cut evidence
for the presence of such natural products in the moss. Therefore, for the time
being, the enzyme should be classified as 'orphan
PKS'.
Eine interessante Frage ist, ob dieses Enzym wohl den "aldol
switch mechanism" verwendet, der mit der
Stilbensynthase (STS) aus der Kiefer (Pinus sylvestris) entdeckt
wurde:
Mehr...
A
related protein in a
Cyanobacterium
a CHS-like enzyme from the
Cyanobacterium
Synechococcus sp. WH 8102
also uses long-chain CoA-esters as starter
substrates and produces in vitro
alkylpyrones and tetraketide alkylresorcinols (depending
on the starter CoA-ester).
The nomenclature is a bit confusing, as
in many cases where independent sequence projects submitted data to the
databases without bothering to check whether the same protein is not already in
the database, but under a different name: The accession number is CAE07508 in the
review article; but the
same protein is in the database with another accession:
NP_897086.
According to the review article, there is not only functional similarity between
the Physcomitrella and the Synechococcus enzyme: in relationship trees
containing both bacterial and plant type III,
PpCHS11 (an alkylresorcinol
synthase, ARS) consistently
positioned next to the Synechococcus protein. The authors argue that this
might be an important clue for understanding the evolution of plant type III PKS,
and they propose that such pyrone synthase and ARS functions may have been
characteristic properties of early type III PKS.
Indeed, resorcinolic lipids are really
wide-spread in bacteria and plants (see a very comprehensive review:
Kozubek and Tyman, 1999).
Eine interessante Frage ist, ob dieses Enzym wohl den "aldol
switch mechanism" verwendet, der mit der
Stilbensynthase (STS) aus der Kiefer (Pinus sylvestris) entdeckt
wurde:
Mehr...
Unfortunately, I did not yet build a
relationship tree that combines plant, fungal, and bacterial enzymes. The only
exception is at present (21.08.2009) a
plant dendrogram which includes the Synechococcus sequence (under the name
CAE07508). It is indeed in a subbranch together with the ARS from P.
patens, and the length of the branch suggests that it is pretty distantly
related to the standard type III PKS and even to the CHS-LK proteins. On the
other hand, its position in a tree
with bacterial type III PKS (here under the name NP_897086) does not suggest
anything unusual, i.e. a particularly large distance to other bacterial proteins
or a closer relationship to plant type III PKS than other bacterial proteins.
Übrigens gibt es Typ
III PKS mit Substrat-Präferenzen für langkettige CoA-Estern häufig
in Pflanzen, Pilzen und Bakterien. Beispiele sind:
-
-
-
-
Alkylresorcinole
und
langkettige Pyrone in dem Bakterium Azotobacter vinelandii:
Mehr...
-
Alkylresorcinol-
Streptomyces
griseus: Mehr...
-
Pyronsynthasen in dem Bakterium
Mycobacterium tuberculosis und
Bacillus subtilis: Mehr...
-
CsyA: Pyronsynthasen
in dem Pilz Aspergillus oryzae:
Mehr...
Direkte Links zu anderen STS-Typ Enzymen
Links zu anderen Beispielen von 'Orphan PKS'
Zum Seitenanfang
Citations
-
Jiang, C., Kim, S. Y., Suh, D.-Y., 2008.
Divergent evolution of the thiolase superfamily and chalcone synthase
family.
Molecular Phylogenetics and Evolution 49, 691-701.
Enzymes of the thiolase superfamily catalyze the formation of
carbon-carbon bond via the Claisen condensation reaction. Thiolases
catalyze the reversible non-decarboxylative condensation of
acetoacetyl-CoA from two molecules of acetyl-CoA, and possess a
conserved Cys-His catalytic diad. Elongation enzymes (beta-ketoacyl-acyl
carrier protein synthase (KAS) I and KAS II and the condensing domain of
polyketide synthase) have invariant Cys and two His residues (CHH
triad), while a Cys-His-Asn (CHN) triad is found in initiation enzymes (KAS
III, 3-ketoacyl-CoA synthase (KCS) and the chalcone synthase (CHS)
family). These enzymes all catalyze decarboxylative condensation
reactions. 3-Hydroxyl-3-methylglutaryl-CoA synthase (HMGS) also contains
the CHN triad, although it catalyzes a non-decarboxylative condensation.
That the enzymes of the thiolase superfamily share overall similarity in
protein structure and function suggested a common evolutionary origin.
All thiolases were found to have, in addition to the Cys-His diad,
either Asn or His (thus C(N/H)H) at a position corresponding to the His
in the CHH and CHN triads. In our phylogenetic analyses, the thiolase
superfamily was divided into four main clusters according to active site
architecture. During the functional divergence of the superfamily, the
active architecture was suggested to evolve from the CHH in archaeal
thiolases to the C(N/H)H in non-archaeal thiolases, and subsequently to
the CHH in the elongation enzymes and the CHN in the initiation enzymes.
Based on these observations and available biochemical and structural
evidences, a plausible evolutionary history for the thiolase superfamily
is proposed that includes the emergence of decarboxylative condensing
enzymes accompanied by a recruitment of the His in the CHH and CHN
triads for a catalytic role during decarboxylative condensation. In
addition, phylogenetic analysis of the plant CHS family showed separate
clustering of CHS and non-CHS members of the family with a few
exceptions, suggesting repeated gene birth-and-death and re-invention of
non-CHS functions throughout the evolution of angiosperms. Based on
these observations, predictions on the enzymatic functions are made for
several members of the CHS family whose functions are yet to be
characterized. Further, a moss CHS-like enzyme that is functionally
similar to a cyanobacterial enzyme was identified as the most recent
common ancestor to the plant CHS family.
Return
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Jiang, C., Schommer, C. K., Kim, S. Y., Suh, D.-Y., 2006.
Cloning and characterization of chalcone synthase from the moss,
Physcomitrella patens. Phytochemistry 67, 2531-2540.
Since the early evolution of land plants from primitive
green algae, flavonoids have played an important role as UV protective
pigments in plants. Flavonoids occur in liverworts and mosses, and the
first committed step in the flavonoid biosynthesis is catalyzed by chalcone
synthase (CHS). Although higher plant CHSs have been extensively studied,
little information is available on the enzymes from bryophytes. Here we
report the cloning and characterization of CHS from the moss,
Physcomitrella patens. Taking advantage of the available P. patens
EST sequences, a CHS (PpCHS) was cloned from the gametophores of P. patens,
and heterologously expressed in Escherichia coli. PpCHS exhibited similar
kinetic properties and substrate preference profile to those of higher
plant CHS. p-Coumaroyl-CoA was the most preferred substrate, suggesting
that PpCHS is a naringenin chalcone producing CHS. Consistent with the
evolutionary position of the moss, phylogenetic analysis placed PpCHS at
the base of the plant CHS clade, next to the microorganism CHS-like gene
products. Therefore, PpCHS likely represents a modern day version of one of
the oldest CHSs that appeared on earth. Further, sequence analysis of the
P. patens EST and genome databases revealed the presence of a CHS
multigene family in the moss as well as the 3'-end heterogeneity of a CHS
gene. Of the 19 putative CHS genes, 10 genes are expressed and have
corresponding ESTs in the databases. A possibility of the functional
divergence of the multiple CHS genes in the moss is discussed.
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Kozubek, A., Tyman, J. H., 1999. Resorcinolic
lipids, the natural non-isoprenoid phenolic amphiphiles and their
biological activity.
Chemical Reviews 99, 1-25.
A very comprehensive interesting review, but no Abstract.
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