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rBPI(21) promotes lipopolysaccharide aggregation and exerts its antimicrobial effects by (hemi)fusion of PG-containing membranes
Publication . Domingues, Marco; Castanho, Miguel A. R. B.; Santos, Nuno C.
Antimicrobial peptides (AMPs) are important potential alternatives to conventional therapies against bacterial infections. rBPI(21) is a 21 kDa peptide based on the N-terminal region of the neutrophil bactericidal/permeability-increasing protein (BPI). This AMP possesses highly selective bactericidal effects on Gram-negative bacteria and have affinity for lipopolysaccharide (LPS) which is believed to be at the origin of its neutralizing effect of the LPS segregated into the bloodstream. We aim at understanding the molecular bases of rBPI(21) bactericidal and LPS neutralization actions, using biomembrane model systems. Using dynamic light scattering spectroscopy we demonstrate that rBPI(21) promotes aggregation of negatively charged large unilamellar vesicles (LUV), even in the absence of LPS, and LPS aggregates, while for zwitterionic phosphatidylcholine (POPC) LUV the size remains unchanged. The peptide also promotes the fusion (or hemifusion) of membranes containing phosphatidylglycerol (POPG). The aggregation and fusion of negatively charged LUV are peptide concentration-dependent until massive aggregation is reached, followed by sample flocculation/precipitation. Concomitantly, there is a progressive change in the zeta-potential of the LUV systems and LPS aggregates. LUV systems composed of phosphatidylglycerol (POPG) and lipid mixtures with POPG have higher zeta-potential variations than in the absence of POPG. The interaction of rBPI(21) with lipid vesicles is followed by leakage, with higher effect in POPG-containing membranes. LPS aggregation can be related with a decreased toxicity, possibly by facilitating its clearance by macrophage phagocytosis and/or blocking of LPS specific receptor recognition. Our data indicate that rBPI(21) mechanism of action at the molecular level involves the interaction with the LPS of the outer membrane of Gram-negative bacteria, followed by internalization and leakage induction through the (hemi)fusion of the bacterial outer and inner membranes, both enriched in phosphatidylglycerol.
Antimicrobial protein rBPI21-induced surface changes on Gram-negative and Gram-positive bacteria
Publication . Domingues, Marco M.; Silva, Patrícia M.; Franquelim, Henri G.; Carvalho, Filomena A.; Castanho, Miguel A. R. B.; Santos, Nuno C.
New classes of antibiotics, such as antimicrobial peptides or proteins (AMPs), are crucial to deal with threatening bacterial diseases. rBPI21 is an AMP based on the human neutrophil BPI protein, with potential clinical use against meningitis. We studied the membrane perturbations promoted by rBPI21 on Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus. Its interaction with bacteria was also studied in the presence of lipopolysaccharide (LPS), rBPI21 major ligand. Flow cytometry analysis of both bacteria shows that rBPI21 induces membrane depolarization. rBPI21 increases the negative surface charge of both bacteria toward positive values, as shown by zeta-potential measurements. This is followed by surface perturbations, culminating in cell lysis, as visualized by atomic force microscopy (AFM). Force spectroscopy measurements show that soluble LPS decreases the interaction of rBPI21 with bacteria, especially with S. aureus. This suggests that the rBPI21 LPS-binding pocket may also participate on the binding to Gram-positive bacteria.
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Fundação para a Ciência e a Tecnologia
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SFRH
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SFRH/BD/41750/2007