Biomedical Engineering Reference
In-Depth Information
l
iPoPePtiDes
Lipopeptides are a class of biosurfactants with the general structure of a cyclic 7-10
amino acid peptide connected to a fatty acid chain. The best studied member of
this class is the anionic surfactant surfactin, produced by
Bacillus subtilis
. Surfactin
has a 7 amino acid peptide head group and a fatty acid chain of 13-16 carbons
(Figure 11.4). Lesser studied members of this class include iturin (7 amino acid pep-
tide with a C14-C17 fatty acid), fengycins (10 amino acid peptide with a C14-C18
fatty acid), and viscosin (9 amino acid peptide and a C10 fatty acid tail group) (Lang,
2002; Saini et al., 2008).
Metal Complexation by Lipopeptides
Early studies of surfactin interaction with cations focused on understanding their
ability to disrupt erythrocyte membranes (Thimon et al., 1992). These studies
showed that surfactin can complex Ca
2+
and Mg
2+
with constants of 1.5 × 10
5
M
−1
and
1.9 × 10
4
M
−1
, respectively (Thimon et al., 1993). More recently, surfactin has been
shown to interact strongly with Fe
3+
, weakly with Cu
2+
, and not at all with Nd
3+
—
biphasic liquid-liquid extraction percentages were >95%, ≈12%, and <5%, respec-
tively (Dejugnat et al., 2011). This binding is associated with the negative charge
generated by two carboxylic groups from the aspartate and glutamate residues of
the peptide structure (Thimon et al., 1992). Spatial arrangement studies of surfactin
suggest that the peptide portion of the molecule forms a “claw-like” structure with
the aspartate and glutamate residues on opposite tips of the claw, creating a position
for metals to bind (Bonmatin et al., 1994). As a result of the two charged groups,
there are different association behaviors of surfactin with mono- and divalent cat-
ions. Divalent cations exhibit a single associated binding constant value that is higher
OO
O
OH
H
NH
HN
O
O
O
HN
O
HN
O
NH
N
HO
O
O
O
FIGURE 11.4
Surfactin produced by
Bacillus subtilis
.
Search WWH ::
Custom Search