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The membranotropic activity of cyclic acyldepsipeptides from bacterium Bacillus pumilus, associated with the marine
N G Prokof'eva1, N I Kalinovskaya, P A Luk'yanov
1Pacific Institute of Bioorganic Chemistry of Far Eastern Branch of the Russian Academy of Sciences, Vladivostok. kuzta@piboc.marine.su
Abstract:
The isolate of Bacillus pumilus associated with the marine sponge Ircinia sp. produced the surfactin-like lipopeptides, cyclic acyldepsipeptides. The hemolytic activity of individual cyclic acyldepsipeptides, bacircines (BI) 2, 3, 4, 5 and 5A having different acyl side chain structures (anteiso-C13, iso-C14, normal-C14, anteiso-C15, and iso-C15, respectively) was studied. The hemolytic power of bacircines depended on both the structure of the side chain (n->iso->anteiso-) and pH values (5.6 and 6.5 > 7.4). Hemolytic potency as a function of BI 5 concentration was given for pH 6.5; 7.4; 8.0; 9.0. pH dependent hemolysis induced by BI 5 was shown to be reversible. The membrane damaging potential of bacircine 5 (5 microM) at pH 6.5 was characterized by a higher rate of hemolysis and by a shorter time between the introduction of BI 5 solution into the RBC samples and the onset of hemolysis. Under this condition, BI 5 decreased abnormally the microviscosity of erythrocyte ghosts bilayer. The damaging potency of BI 5 decreased with an increase pH from 6.5 to 7.4 or its decrease from 6.5 to 4.9. It was shown that fatty acid bacircine fragment penetrated into the lipid bilayer to a depth of minimum 7 carbon atoms. Constants of dissociation of the Asp (pK 4.75) and Glu (pK 6.65) residues of bacircine in the lipid bilayer were obtained. These results showed that at pH 6.5 BI 5 possessed membranotropic activity in the monoionic form.
Insights
Marine bacteria produce cyclic acyldepsipeptides called bacircines that damage cell membranes. Their hemolytic activity depends on side chain structure and pH, with bacircine 5 showing potent membrane disruption at pH 6.5.
Area of Science:
- Marine microbiology
- Biochemistry
- Lipid bilayer interactions
Background:
- Bacillus pumilus associated with marine sponge Ircinia sp. produces surfactin-like lipopeptides.
- These compounds are cyclic acyldepsipeptides, specifically identified as bacircines (BI).
- Previous studies have indicated potential biological activities of these lipopeptides.
Purpose of the Study:
- To investigate the hemolytic activity of various bacircines.
- To determine the influence of acyl side chain structure and pH on hemolytic potency.
- To characterize the membrane-damaging mechanism of bacircine 5.
Main Methods:
- Synthesis and purification of bacircines (BI 2, 3, 4, 5, 5A) with varying acyl side chains.
- Hemolysis assays using red blood cells (RBCs) at different pH values and bacircine concentrations.
- Measurement of erythrocyte ghost bilayer microviscosity.
- Determination of dissociation constants for Asp and Glu residues within the lipid bilayer.
Main Results:
- Hemolytic activity of bacircines is dependent on both acyl side chain structure (n->iso->anteiso-) and pH (optimal at 5.6-6.5).
- Bacircine 5 demonstrated significant membrane-damaging potential at pH 6.5, characterized by rapid hemolysis and decreased lipid bilayer microviscosity.
- The damaging potency of bacircine 5 decreased at pH values above 6.5 or below 4.9, indicating pH-dependent activity.
- Fatty acid fragment of bacircine penetrated the lipid bilayer to a depth of at least 7 carbon atoms.
- Dissociation constants for Asp (pK 4.75) and Glu (pK 6.65) residues were determined in the lipid bilayer.
Conclusions:
- Bacircines exhibit pH-dependent hemolytic activity, with optimal potency at acidic to neutral pH.
- Bacircine 5 possesses strong membranotropic activity at pH 6.5, likely due to its monoionic form and interaction with the lipid bilayer.
- The study elucidates the mechanism of membrane damage by bacircines, highlighting their potential as bioactive compounds.