Biology Reference
In-Depth Information
Figure 6.14
Thegenecluster
crp
responsibleforthebiosynthesisofcryptophycin1in
Nostoc punctiforme
ATCC53789.Seethecolourplate.
4.3.2. Nostophycins
Nostophycin has been isolated from
Nostoc
sp. strain 152. It is a cyclic hep-
tapeptide containing a β-amino acid residue, the (2
S
, 3
R
, 5
R
)-amino-2,
5-dihydroxy-8-phenyloctanoate (Ahoa) (
Fujii, Sivonen, Kashiwagi,
Hirayama, & Harada, 1999
). The biosynthetic cluster,
npn
, has been identi-
fied in the producing strain, and it consists of three genes coding for one
PKS, one PKS/NRPS hybrid and one NRPS (
Fewer et al., 2011
). A bio-
synthetic scheme has been proposed based on the analysis of the sequence
of the cluster. The specificities of the isolated adenylation domains were
studied in vitro and they showed promiscuous selectivity, suggesting that
variants of nostophycin should be observed (
Fewer et al., 2011
). As in the
case of microcystin and cryptophycin biosynthesis, the starter of the first
PKS, NpnA, is not known and the exact mechanism leading to the probable
loss of one carbon remains elusive.
4.3.3. Nostocyclopeptides and nostopeptolides
Nostocyclopeptides are cycloheptapeptides produced by
Nostoc
sp. ATCC
53789 (
Golakoti, Yoshida, Chaganty, & Moore, 2001
). These peptides con-
tain a 4-methylprolyl residue and an imine linkage. The 33-kb cluster,
ncp
,
has been identified and sequenced from the producer, and it codes for two
NRPSs and for five other genes, among which the
ncpE
gene involved in the
biosynthesis of the 4-methylproline amino acid (
Becker, Moore, & Moore,
2004
). The formation of imine linkage is rather unique and involves a reduc-
tive domain found at the C-terminal end of NcpB, the last PKS of this
biosynthesis. Nostopeptolide A is a hybrid PK/NRP produced by the cya-
nobacterium
Nostoc
sp. GSV224, and it contains a leucylacetate unit and, like
nostocyclopeptides, a 4-methylprolyl residue (
Golakoti, Yoshida, Chaganty,
& Moore, 2000
). The biosynthetic cluster
nos
was identified and sequenced
in
Nostoc
sp. GSV224 (
Hoffmann, Hevel, Moore, & Moore, 2003
). The genes,
nosE
and
nosF
, responsible for the biosynthesis of the 4-methylproline are
part of the cluster, and a biosynthetic scheme for 4-methylproline was pro-
posed starting from leucine, and confirmed in vitro (
Luesch et al., 2003
).
