1.D.11 The Surfactin (Surfactin) Family
Surfactin is an acidic lipopeptide produced by Bacillus subtilis strains. At high concentrations (above its critical micellar concentration (CMC) of 9 μM) it is a biosurfactant. It is also an antibacterial, antiviral, antitumor agent that lyses erythrocytes and inhibits formation of fibrin clots. At low concentrations (below its CMC) it forms pores in membranes (Carrillo et al., 2003), allowing leakage of carboxyfluorescein from unilamellar vesicles. Its activity is dependent on the lipid composition of the vesicles. It interacts with the phospholipid acyl chains.
Surfactin is a cyclic lactone peptide of 7 aas. The structure is provided in Carrillo et al. (2003). It is made by surfactin synthetase (BAA02523), a 3072 aa, multidomain protein in which each domain catalyzes the addition of a different D- or L-amino acid to the growing chain.
Bacillus subtilis and other Bacilllus species make a large number of non-ribosomally synthesized (lipo)peptides related to surfactin. These include plipistatin A1 and B1, inhibitors of phospholipase A2, bacillomycins D and L, which inhibit growth of the aflatoxin-producing fungus Aspergillus flavus as well as other fungi and bacteria, Iturin A, which has been shown to inhibit fungal and bacterial growth by forming membrane pores that cause K+ permeability (Thaniyavarn et al. 2003), and Mycosubtilin, which resembles iturin A (Moyne et al. 2004). Intergenic module repoacements have occurred between the varous lipopeptide synthetases (Thaniyavarn et al. 2003).
The transport reaction catalyzed by surfactin and other similar lipopeptides is:
small molecules (in) small molecules (out)