Biology Reference
In-Depth Information
that allowed a prediction of the enzymes necessary to produce the mol-
ecule. The putative
cur
cluster was identified using a cosmid library from
L. majuscula
that was screened by southern hybridization. Several clusters
were then identified, sequenced, and analysed by bioinformatics, and one
cluster matched the predicted
cur
cluster. This 64-kb cluster contains 14
genes including several PKSs (
Chang et al., 2004
;
Gu, Wang, Kulkarni,
Geders, et al., 2009
;
Gu, Wang, Kulkarni, Gehret, et al., 2009
). The last
step of this biosynthesis is quite remarkable, and involves a sulfatation,
followed by a decarboxylation and elimination, to give the terminal dou-
ble bond. These steps have been studied in vitro using isolated domains
(
Gu, Wang, Kulkarni, Geders, et al., 2009
;
Gu, Wang, Kulkarni, Gehret,
et al., 2009
).
4.4.3. Jamaicamides
Jamaicamide A-C are mixed PK/NRPs produced by
L. majuscula
. They
are blockers of the sodium channel and show toxicity towards fishes. The
biosynthesis of these lipopeptides was studied by stable isotope incorpora-
tion, and the biosynthetic gene cluster was then identified by using a combi-
nation of PCR amplifications and southern hybridizations. The
jam
cluster
contains 17 genes including eight genes coding for PKSs. A biosynthetic
scheme was proposed based on the analysis of the
jam
cluster (
Edwards
et al., 2004
). There are several interesting chemical motifs in jamaicamide,
the triple carbon-carbon bond and the chlorovinyl group. The formation of
the vinyl chloride motif has been studied and it parallels the formation of
the cyclopropane ring of curacin (
Gu, Wang, Kulkarni, Geders, et al., 2009
;
Gu, Wang, Kulkarni, Gehret, et al., 2009
).
4.5. Ribosomal Peptides
Cyanobacteria produce many RPs that are sometimes greatly modified
by processing enzymes acting post-translationally. These RPs fall into sev-
eral classes, such as the cyanobactins (
Sivonen, Leikoski, Fewer, & Jokela,
2010
), the microviridins (
Ziemert, Ishida, Liaimer, et al., 2008
;
Ziemert,
Ishida, Quillardet, et al., 2008
), the bacteriocins (
Wang, Fewer, et al., 2011
;
Wang, Xu, et al., 2011
), or the lantipeptides (
Li et al., 2010
). Because the
peptide core of the RP is derived from a precursor, the clusters of genes
responsible of the biosynthesis of RP are usually small with only a few
genes coding for the modifying enzymes. We shall briefly present two
classes of RP, the cyanobactins and the microviridins with emphasis on
the former.
