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Cationic Antimicrobial Peptides (AMPs): Thermodynamic Characterization of Peptide-Lipid Interactions and Biological Efficacy of Surface-Tethered Peptides.

Bagheri M - ChemistryOpen (2015)

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry, Institute of Biochemistry & Biophysics, University of Tehran P.O. Box: 13145-1365, 16 Azar St., 1417614411, Tehran, Iran.

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Unlike the cholesterol-rich electrically neutral lipid membrane of eukaryotic cells, responsible for low peptide affinity and insertion, the bacterial cytoplasmic membrane possesses negatively charged phospholipids that, together with additional cellular envelope features such as the lipopolysaccharide (LPS) and peptidoglycans in Gram-negative and Gram-positive bacteria, respectively, represent ideal targets for cationic AMPs binding... In this doctoral research, the structural basis of activity of short cyclic AMPs rich in arginine and tryptophan residues, as promising anti-E.  coli candidates, was studied to understand membrane constituents and the peptide structural motif important for selectivity against Gram-negative bacteria... In particular, we sought to understand how a) the physical properties of the resin, such as the spacer length between the solid matrix and the AMP, as well as the capacity of the functional groups on the surface, and b) the tethering at different positions (peptide termini and side chain) affect the activities of the tethered AMPs. cyclo-RRRWFW (c-WFW) shows excellent activities against various strains of bacteria (in particular Gram-negative such as E.  coli) compared with its linear analogue, Ac-RRRWFW (Ac-WFW)... The roles of both the arginine and tryptophan residues in biological and bilayer permeabilizing activities are described for several peptide variants... The susceptibility of Gram-negative bacteria to c-WFW was proposed to be associated with factors that facilitate the transport of the peptide across the LPS. c-WFW is most active against the smooth LPS strain (wild type), while reduction of sugar chains in mutated LPS strain (rough type) distinctly decreases the antimicrobial effect... While the significant role of tryptophan residues in many LPS-binding motifs of AMPs is known, studies on the structural motifs of c-WFW in particular from the point of selective interactions between the aromatic side chain of tryptophan residues and distinct regions of LPS, which are important for its anti-E.  coli activity, needed to be done... In the presence of lipid A, rough-LPS and smooth-LPS, the dominant role of hydrophobicity decreased among the cyclic peptides with no influence on the weak affinity of the highly flexible linear Ac-WFW... The higher hydrophobic partition coefficients for the peptide interaction with POPC/smooth-LPS compared with POPC/rough-LPS lipid bilayers underlined the modulating effects of the O-antigen and the oligosaccharides in the outer core of LPS in the peptide activity and transport across the E.  coli outer wall... Specifically, the distance between the solid surface and the active sequences was identified as a critical parameter for peptide activity... The AMPs effectiveness decreased with decreasing spacer length, regardless of the amount of peptide on the surface... Immobilization of membrane-permeabilizing sequences was found to be most suitable for the generation of antimicrobial surfaces... Immobilization did not influence the activity pattern and conserved the peptide membrane-permeabilizing mode of action.

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a) Antimicrobial and b) hemolytic activities of cyclic peptide derivatives. MIC values are the minimal concentration of peptide required to inhibit bacterial growth. The hemolytic activity was determined at a peptide concentration of 200 μm; note, c-(5fW)F(5fW) was not evaluated. The peptides were nontoxic at their MIC values. Values shown in panel b represent the HPLC retention time (tR). ND: not determined.
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fig01: a) Antimicrobial and b) hemolytic activities of cyclic peptide derivatives. MIC values are the minimal concentration of peptide required to inhibit bacterial growth. The hemolytic activity was determined at a peptide concentration of 200 μm; note, c-(5fW)F(5fW) was not evaluated. The peptides were nontoxic at their MIC values. Values shown in panel b represent the HPLC retention time (tR). ND: not determined.

Mentions: The antimicrobial and hemolytic activities of the peptides were evaluated against E. coli, Bacillus subtilis and red blood cells (Figure 1). The peptide ability to permeabilize the inner and outer membrane of E. coli was also investigated. Isothermal titration calorimetric (ITC) studies were carried out to provide information on peptide interaction with POPC and POPC/POPG bilayers, and with lipid A, rough-LPS and smooth-LPS incorporated in POPC bilayers (as models of the outer membrane of Gram-negative bacteria). The results from this study showed that peptide hydrophobicity and backbone constraints are the crucial determinants of biological activity. The different susceptibilities of E. coli and B. subtilis could be explained by differences in the negative surface charge of the plasma membranes (Figure 1 a). Additionally, interaction with the outer membrane LPS of E. coli is responsible for the complex activity pattern. The peptides permeabilized the outer membrane according to their anti-E. coli activity spectrum, suggesting LPS as the crucial modulator of activity. Low hydrophobicity and conformational flexibility of peptides decreases their affinity for the lipid layers (Figure 2). In the presence of lipid A, rough-LPS and smooth-LPS, the dominant role of hydrophobicity decreased among the cyclic peptides with no influence on the weak affinity of the highly flexible linear Ac-WFW. The higher hydrophobic partition coefficients for the peptide interaction with POPC/smooth-LPS compared with POPC/rough-LPS lipid bilayers underlined the modulating effects of the O-antigen and the oligosaccharides in the outer core of LPS in the peptide activity and transport across the E. coli outer wall.


Cationic Antimicrobial Peptides (AMPs): Thermodynamic Characterization of Peptide-Lipid Interactions and Biological Efficacy of Surface-Tethered Peptides.

Bagheri M - ChemistryOpen (2015)

a) Antimicrobial and b) hemolytic activities of cyclic peptide derivatives. MIC values are the minimal concentration of peptide required to inhibit bacterial growth. The hemolytic activity was determined at a peptide concentration of 200 μm; note, c-(5fW)F(5fW) was not evaluated. The peptides were nontoxic at their MIC values. Values shown in panel b represent the HPLC retention time (tR). ND: not determined.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4522190&req=5

fig01: a) Antimicrobial and b) hemolytic activities of cyclic peptide derivatives. MIC values are the minimal concentration of peptide required to inhibit bacterial growth. The hemolytic activity was determined at a peptide concentration of 200 μm; note, c-(5fW)F(5fW) was not evaluated. The peptides were nontoxic at their MIC values. Values shown in panel b represent the HPLC retention time (tR). ND: not determined.
Mentions: The antimicrobial and hemolytic activities of the peptides were evaluated against E. coli, Bacillus subtilis and red blood cells (Figure 1). The peptide ability to permeabilize the inner and outer membrane of E. coli was also investigated. Isothermal titration calorimetric (ITC) studies were carried out to provide information on peptide interaction with POPC and POPC/POPG bilayers, and with lipid A, rough-LPS and smooth-LPS incorporated in POPC bilayers (as models of the outer membrane of Gram-negative bacteria). The results from this study showed that peptide hydrophobicity and backbone constraints are the crucial determinants of biological activity. The different susceptibilities of E. coli and B. subtilis could be explained by differences in the negative surface charge of the plasma membranes (Figure 1 a). Additionally, interaction with the outer membrane LPS of E. coli is responsible for the complex activity pattern. The peptides permeabilized the outer membrane according to their anti-E. coli activity spectrum, suggesting LPS as the crucial modulator of activity. Low hydrophobicity and conformational flexibility of peptides decreases their affinity for the lipid layers (Figure 2). In the presence of lipid A, rough-LPS and smooth-LPS, the dominant role of hydrophobicity decreased among the cyclic peptides with no influence on the weak affinity of the highly flexible linear Ac-WFW. The higher hydrophobic partition coefficients for the peptide interaction with POPC/smooth-LPS compared with POPC/rough-LPS lipid bilayers underlined the modulating effects of the O-antigen and the oligosaccharides in the outer core of LPS in the peptide activity and transport across the E. coli outer wall.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry, Institute of Biochemistry & Biophysics, University of Tehran P.O. Box: 13145-1365, 16 Azar St., 1417614411, Tehran, Iran.

AUTOMATICALLY GENERATED EXCERPT
Please rate it.

Unlike the cholesterol-rich electrically neutral lipid membrane of eukaryotic cells, responsible for low peptide affinity and insertion, the bacterial cytoplasmic membrane possesses negatively charged phospholipids that, together with additional cellular envelope features such as the lipopolysaccharide (LPS) and peptidoglycans in Gram-negative and Gram-positive bacteria, respectively, represent ideal targets for cationic AMPs binding... In this doctoral research, the structural basis of activity of short cyclic AMPs rich in arginine and tryptophan residues, as promising anti-E.  coli candidates, was studied to understand membrane constituents and the peptide structural motif important for selectivity against Gram-negative bacteria... In particular, we sought to understand how a) the physical properties of the resin, such as the spacer length between the solid matrix and the AMP, as well as the capacity of the functional groups on the surface, and b) the tethering at different positions (peptide termini and side chain) affect the activities of the tethered AMPs. cyclo-RRRWFW (c-WFW) shows excellent activities against various strains of bacteria (in particular Gram-negative such as E.  coli) compared with its linear analogue, Ac-RRRWFW (Ac-WFW)... The roles of both the arginine and tryptophan residues in biological and bilayer permeabilizing activities are described for several peptide variants... The susceptibility of Gram-negative bacteria to c-WFW was proposed to be associated with factors that facilitate the transport of the peptide across the LPS. c-WFW is most active against the smooth LPS strain (wild type), while reduction of sugar chains in mutated LPS strain (rough type) distinctly decreases the antimicrobial effect... While the significant role of tryptophan residues in many LPS-binding motifs of AMPs is known, studies on the structural motifs of c-WFW in particular from the point of selective interactions between the aromatic side chain of tryptophan residues and distinct regions of LPS, which are important for its anti-E.  coli activity, needed to be done... In the presence of lipid A, rough-LPS and smooth-LPS, the dominant role of hydrophobicity decreased among the cyclic peptides with no influence on the weak affinity of the highly flexible linear Ac-WFW... The higher hydrophobic partition coefficients for the peptide interaction with POPC/smooth-LPS compared with POPC/rough-LPS lipid bilayers underlined the modulating effects of the O-antigen and the oligosaccharides in the outer core of LPS in the peptide activity and transport across the E.  coli outer wall... Specifically, the distance between the solid surface and the active sequences was identified as a critical parameter for peptide activity... The AMPs effectiveness decreased with decreasing spacer length, regardless of the amount of peptide on the surface... Immobilization of membrane-permeabilizing sequences was found to be most suitable for the generation of antimicrobial surfaces... Immobilization did not influence the activity pattern and conserved the peptide membrane-permeabilizing mode of action.

No MeSH data available.