Progress in the Chemistry of Cytochalasans
85
cluster in C. globosum also contained several tailoring enzymes such as two P450
oxygenases (CHGG_01242-1 and CHGG_01243), a FAD-dependent monooxygenase (CHGG_1242-2), as well as a transcription factor (CHGG_01237). However,
two additional genes encoding proteins of unknown function CHGG_01241 and
CHGG_01244 were identified. The latter encoded a protein with sequence similarity
to α,β-hydrolases. Targeted gene deletion of CHGG_01239 and CHGG_01240 led
to the abrogation of chaetoglobosin A (208) production in C. globosum, confirming
the function of the cluster.
The biosynthesis of cytochalasin E (139) and cytochalasin K (140) in Aspergillus
clavatus has been determined as being achieved by gene cluster ccs (Fig. 21D)
[260]. The involvement of PKS–NRPS encoded by the gene ccsA in ccs cluster was
confirmed by gene disruption. Bioinformatic analysis of this cluster revealed a transER (CcsC), two P450 monooxygenases (CcsD and CcsG), a transcriptional regulator
(CcsR), two proteins of unknown function (CcsE and CcsF), as well as a unique
Baeyer–Villiger monooxygenase (BVMO, CcsB), which could catalyze previously
proposed reactions, so that an oxygen atom may be inserted in the backbone forming
the vinyl carbonate moiety in cytochalasin E (139) [240]. CcsE shows a sequence
similarity to an α,β-hydrolase and shares a 54% identity with CHGG_01244, while
CcsF shares a 51% sequence identity with CHGG_01241 from C. globosum. CcsF has
previously been suggested to be involved in the intramolecular [4 + 2] Diels–Alder
cycloaddition reaction, so for simplicity, CcsF and its homologs in other cytochalasan
gene clusters, for example CHGG_01241 shall be referred to as putative Diels–
Alderases (pDA) [2].
The pyrichalasin H (164) gene cluster, pyi, was identified through genome
mining in Magnaporthe grisea (Fig. 21E) [8]. The function of this cluster was
confirmed by disruption of the PKS–NRPS encoding gene pyiS, which resulted in
the complete abolishment of pyrichalasin H (164) production. An investigation of
the cluster pyi revealed that it has a high similarity to the ACE1 gene cluster in M.
oryzae Guy11 [249]. Besides the PKS–NRPS, cluster pyi contains genes encoding a
trans-ER (pyiC), α,β-hydrolases (pyiE), a pDA (pyiF), two P450 monooxygenases
(pyiD and pyiG), an oxidoreductase (pyiH), an O-methyltransferase (pyiA), an Oacetyltransferase (pyiB), a transporter (pyiT ) and a transcriptional regulator (pyiR),
respectively. On comparing to other characterized cytochalasan gene clusters, two
additional tailoring genes, pyiA and pyiB, were characterized as being involved in the
formation of the para-methoxyphenyl and O-acetyl groups in pyrichalasin H (164),
respectively [8].
Genome sequencing of the fungus, Hypoxylon fragiforme MUCL 51264, which
produces cytochalasin H (7) and several analogs, revealed the gene cluster hff [55].
Compared to the pyi cluster in M. grisea NI980 that encodes cytochalasin H (7),
homologous biosynthesis genes encoding a PKS-NRPS (hffS), a trans-ER (hffC), a
putative Diels–Alderase (hffF), an α,β-hydrolase (hffE), two P450s (hffD and hffG),
an oxido-reductase (hffH), an acetyltransferase (hffB), a transporter (hffT ), and a transcription factor (hffR) were identified in cluster hff (Fig. 21F). Although a systematic
functional investigation of cluster hff has not yet been reported, two P450 genes (hffD
and hffG) in this gene cluster were confirmed to have the catalytic abilities to restore
85
cluster in C. globosum also contained several tailoring enzymes such as two P450
oxygenases (CHGG_01242-1 and CHGG_01243), a FAD-dependent monooxygenase (CHGG_1242-2), as well as a transcription factor (CHGG_01237). However,
two additional genes encoding proteins of unknown function CHGG_01241 and
CHGG_01244 were identified. The latter encoded a protein with sequence similarity
to α,β-hydrolases. Targeted gene deletion of CHGG_01239 and CHGG_01240 led
to the abrogation of chaetoglobosin A (208) production in C. globosum, confirming
the function of the cluster.
The biosynthesis of cytochalasin E (139) and cytochalasin K (140) in Aspergillus
clavatus has been determined as being achieved by gene cluster ccs (Fig. 21D)
[260]. The involvement of PKS–NRPS encoded by the gene ccsA in ccs cluster was
confirmed by gene disruption. Bioinformatic analysis of this cluster revealed a transER (CcsC), two P450 monooxygenases (CcsD and CcsG), a transcriptional regulator
(CcsR), two proteins of unknown function (CcsE and CcsF), as well as a unique
Baeyer–Villiger monooxygenase (BVMO, CcsB), which could catalyze previously
proposed reactions, so that an oxygen atom may be inserted in the backbone forming
the vinyl carbonate moiety in cytochalasin E (139) [240]. CcsE shows a sequence
similarity to an α,β-hydrolase and shares a 54% identity with CHGG_01244, while
CcsF shares a 51% sequence identity with CHGG_01241 from C. globosum. CcsF has
previously been suggested to be involved in the intramolecular [4 + 2] Diels–Alder
cycloaddition reaction, so for simplicity, CcsF and its homologs in other cytochalasan
gene clusters, for example CHGG_01241 shall be referred to as putative Diels–
Alderases (pDA) [2].
The pyrichalasin H (164) gene cluster, pyi, was identified through genome
mining in Magnaporthe grisea (Fig. 21E) [8]. The function of this cluster was
confirmed by disruption of the PKS–NRPS encoding gene pyiS, which resulted in
the complete abolishment of pyrichalasin H (164) production. An investigation of
the cluster pyi revealed that it has a high similarity to the ACE1 gene cluster in M.
oryzae Guy11 [249]. Besides the PKS–NRPS, cluster pyi contains genes encoding a
trans-ER (pyiC), α,β-hydrolases (pyiE), a pDA (pyiF), two P450 monooxygenases
(pyiD and pyiG), an oxidoreductase (pyiH), an O-methyltransferase (pyiA), an Oacetyltransferase (pyiB), a transporter (pyiT ) and a transcriptional regulator (pyiR),
respectively. On comparing to other characterized cytochalasan gene clusters, two
additional tailoring genes, pyiA and pyiB, were characterized as being involved in the
formation of the para-methoxyphenyl and O-acetyl groups in pyrichalasin H (164),
respectively [8].
Genome sequencing of the fungus, Hypoxylon fragiforme MUCL 51264, which
produces cytochalasin H (7) and several analogs, revealed the gene cluster hff [55].
Compared to the pyi cluster in M. grisea NI980 that encodes cytochalasin H (7),
homologous biosynthesis genes encoding a PKS-NRPS (hffS), a trans-ER (hffC), a
putative Diels–Alderase (hffF), an α,β-hydrolase (hffE), two P450s (hffD and hffG),
an oxido-reductase (hffH), an acetyltransferase (hffB), a transporter (hffT ), and a transcription factor (hffR) were identified in cluster hff (Fig. 21F). Although a systematic
functional investigation of cluster hff has not yet been reported, two P450 genes (hffD
and hffG) in this gene cluster were confirmed to have the catalytic abilities to restore