5 research outputs found
Pattern Formation in the BromateāSulfiteāFerrocyanide Reaction
Mixed Landolt-type pH oscillators
are versatile systems that allow
the experimental study of a wide range of nonlinear phenomena including
multistability, oscillations, and spatiotemporal patterns. We report
on the dynamics of the bromateāsulfiteāferrocyanide
reaction operated in a open one-side-fed reactor, where spatial bistability,
spatiotemporal oscillations, front and Turing-type patterns have been
observed. The role of different experimental parameters, like the
input flow concentrations of the hydrogen and the ferrocyanide ions,
the temperature and the thickness of the gel medium (which affects
the rate of the diffusive feed) have been investigated. We point out
that all these parameters can be efficiently used to control the spatiotemporal
dynamics. We show that the increase of ionic strength stabilizes the
uniform states at the expense of the patterned one. Some general aspects
of the spatiotemporal dynamics of mixed Landolt type systems, which
are based on the oxidation of sulfite ions by strong oxidants, are
emphasized
Pattern Formation in the BromateāSulfiteāFerrocyanide Reaction
Mixed Landolt-type pH oscillators
are versatile systems that allow
the experimental study of a wide range of nonlinear phenomena including
multistability, oscillations, and spatiotemporal patterns. We report
on the dynamics of the bromateāsulfiteāferrocyanide
reaction operated in a open one-side-fed reactor, where spatial bistability,
spatiotemporal oscillations, front and Turing-type patterns have been
observed. The role of different experimental parameters, like the
input flow concentrations of the hydrogen and the ferrocyanide ions,
the temperature and the thickness of the gel medium (which affects
the rate of the diffusive feed) have been investigated. We point out
that all these parameters can be efficiently used to control the spatiotemporal
dynamics. We show that the increase of ionic strength stabilizes the
uniform states at the expense of the patterned one. Some general aspects
of the spatiotemporal dynamics of mixed Landolt type systems, which
are based on the oxidation of sulfite ions by strong oxidants, are
emphasized
Insights into the Biosynthesis of 12-Membered Resorcylic Acid Lactones from Heterologous Production in <i>Saccharomyces cerevisiae</i>
The phytotoxic fungal polyketides
lasiodiplodin and resorcylide
inhibit human blood coagulation factor XIIIa, mineralocorticoid receptors,
and prostaglandin biosynthesis. These secondary metabolites belong
to the 12-membered resorcylic acid lactone (RAL<sub>12</sub>) subclass
of the benzenediol lactone (BDL) family. Identification of genomic
loci for the biosynthesis of lasiodiplodin from <i>Lasiodiplodia
theobromae</i> and resorcylide from <i>Acremonium zeae</i> revealed collaborating iterative polyketide synthase (iPKS) pairs
whose efficient heterologous expression in <i>Saccharomyces cerevisiae</i> provided a convenient access to the RAL<sub>12</sub> scaffolds desmethyl-lasiodiplodin
and <i>trans</i>-resorcylide, respectively. Lasiodiplodin
production was reconstituted in the heterologous host by co-expressing
an <i>O</i>-methyltransferase also encoded in the lasiodiplodin
cluster, while a glutathione-<i>S</i>-transferase was found
not to be necessary for heterologous production. Clarification of
the biogenesis of known resorcylide congeners in the heterologous
host helped to disentangle the roles that biosynthetic irregularities
and chemical interconversions play in generating chemical diversity.
Observation of 14-membered RAL homologues during <i>in vivo</i> heterologous biosynthesis of RAL<sub>12</sub> metabolites revealed
āstutteringā by fungal iPKSs. The close global and domain-level
sequence similarities of the orthologous BDL synthases across different
structural subclasses implicate repeated horizontal gene transfers
and/or cluster losses in different fungal lineages. The absence of
straightforward correlations between enzyme sequences and product
structural features (the size of the macrocycle, the conformation
of the exocyclic methyl group, or the extent of reduction by the hrPKS)
suggest that BDL structural variety is the result of a select few
mutations in key active site cavity positions
Diversity-Oriented Combinatorial Biosynthesis of Hybrid Polyketide Scaffolds from Azaphilone and Benzenediol Lactone Biosynthons
Two
disparate polyketide families, the benzenediol lactones and
the azaphilones, are produced by fungi using iterative polyketide
synthase (iPKS) enzymes consisting of collaborating partner subunits.
Exploitation of this common biosynthetic logic using iPKS subunit
shuffling allowed the diversity-oriented combinatorial biosynthesis
of unprecedented polyketide scaffolds new to nature, bearing structural
motifs from both of these orthogonal natural product families. Starter
unit acyltransferase domain replacements proved necessary but not
sufficient to guarantee communication between iPKS subunits
Biosynthesis of Cytosporones in Leotiomycetous Filamentous Fungi
Polyketides
with the isochroman-3-one pharmacophore are rare among
fungal natural products as their biosynthesis requires an unorthodox
S-type aromatic ring cyclization. Genome mining uncovered a conserved
gene cluster in select leotiomycetous fungi that encodes the biosynthesis
of cytosporones, including isochroman-3-one congeners. Combinatorial
biosynthesis in total biosynthetic and biocatalytic formats in Saccharomyces cerevisiae and in vitro reconstitution
of key reactions with purified enzymes revealed how cytosporone structural
and bioactivity diversity is generated. The S-type acyl dihydroxyphenylacetic
acid (ADA) core of cytosporones is assembled by a collaborating polyketide
synthase pair. Thioesterase domain-catalyzed transesterification releases
ADA esters, some of which are known Nur77 modulators. Alternatively,
hydrolytic release allows C6 hydroxylation by a flavin-dependent monooxygenase,
yielding a trihydroxybenzene moiety. Reduction of the C9 carbonyl
by a short chain dehydrogenase/reductase initiates isochroman-3-one
formation, affording cytosporones with cytotoxic and antimicrobial
activity. Enoyl di- or trihydroxyphenylacetic acids are generated
as shunt products, while isocroman-3,4-diones are formed by autoxidation.
The cytosporone pathway offers novel polyketide biosynthetic enzymes
for combinatorial synthetic biology to advance the production of āunnaturalā
natural products for drug discovery