Biology Reference
In-Depth Information
Figure 6.16
Comparisonofthecyanobactinclustersresponsibleforthebiosynthesisof
patellamideandmicrocyclamide.Seethecolourplate.
recognition sequence and performs the macrocyclization. These catalytic
events lead to the cyclic peptide that will eventually be prenylated by the
PatF or homologous enzymes. The fact that the leader sequence and the
protease recognition sequences are conserved in the precursors of cyano-
bactins has led to successful predictions of cyanobactin structures in diverse
cyanobacteria. Another interesting aspect of this pathway is that it is possible
to create cyclic peptides in a combinatorial manner by introducing variable
and unnatural sequences within the proteases recognition sequences in the
precursor (
Tianero, Donia, Young, Schultz, & Schmidt, 2012
).
4.5.2. Microviridins
Microviridins are RPs produced by different genera of cyanobacteria, such
as
Microcystis
,
Oscillatoria
, or
Planktothrix
. These peptides bear a unique tri-
cyclic structure with two lactone bonds and a lactam bond. They show
interesting biological properties such as inhibition of proteases. The biosyn-
thetic gene clusters,
mdn
and
mvd
, have been identified and sequenced in
several strains (see
Table 6.1
). The
mdn
cluster from
M. aeruginosa
NIES 298
contains five genes. On this basis, a biosynthesis for microviridin B has been
proposed: the precursor MdnA that contains an N-terminal leader sequence
followed by the microviridin sequence is first processed by two ATP grasp
proteins, MdnC and MdnB, in a sequential manner to form the three cyclic
moiety (
Philmus, Christiansen, Yoshida, & Hemscheidt, 2008
;
Philmus,
Guerrette, Hemscheidt et al., 2009
;
Ziemert, Ishida, Liaimer, et al., 2008
;
Ziemert, Ishida, Quillardet, et al., 2008
,
Ziemert, Ishida, Weiz, Hertweck, &
Dittmann, 2010
). The peptide is then presumably cleaved and acetylated by
