Antimicrobial Action of Prototypic Amphipathic Cationic Decapeptides and Their Branched Dimers

Self Cite

By choosing membranes as targets of action, antibacterial peptides offer the promise of providing antibiotics to which bacteria would not become resistant. However, there is a need to increase their potency against bacteria along with achieving a reduction in toxicity to host cells. Here, we report that three de novo-designed antibacterial peptides (⌬Fm, ⌬Fmscr, and Ud) with poor to moderate antibacterial potencies and kill kinetics improved significantly in all of these aspects when synergized with rifampin and kanamycin against Escherichia coli. (⌬Fm and ⌬Fmscr [a scrambled-sequence version of ⌬Fm] are isomeric, monomeric decapeptides containing the nonproteinogenic amino acid ␣,␤-didehydrophenylalanine [⌬F] in their sequences. Ud is a lysine-branched dimeric peptide containing the helicogenic amino acid ␣-aminoisobutyric acid [Aib].) In synergy with rifampin, the MIC of ⌬Fmscr showed a 34-fold decrease (67.9 g/ml alone, compared to 2 g/ml in combination). A 20-fold improvement in the minimum bactericidal concentration of Ud was observed when the peptide was used in combination with rifampin (369.9 g/ml alone, compared to 18.5 g/ml in combination). Synergy with kanamycin resulted in an enhancement in kill kinetics for ⌬Fmscr (no killing until 60 min for ⌬Fmscr alone, versus 50% and 90% killing within 20 min and 60 min, respectively, in combination with kanamycin). Combination of the dendrimeric peptide ⌬Fq (a K-K2 dendrimer for which the sequence of ⌬Fm constitutes each of the four branches) (MIC, 21.3 g/ml) with kanamycin (MIC, 2.1 g/ml) not only lowered the MIC of each by 4-fold but also improved the therapeutic potential of this highly hemolytic (37% hemolysis alone, compared to 4% hemolysis in combination) and cytotoxic (70% toxicity at 10؋ MIC alone, versus 30% toxicity in combination) peptide. Thus, synergy between peptide and nonpeptide antibiotics has the potential to enhance the potency and target selectivity of antibacterial peptides, providing regimens which are more potent, faster acting, and safer for clinical use.

Section: Discussionmentioning

confidence: 82%

Synergy with Rifampin and Kanamycin Enhances Potency, Kill Kinetics, and Selectivity ofDeNovo-Designed Antimicrobial Peptides

Anantharaman

Rizvi

Sahal

2010

Self Cite

“…Peptides varying from 10 to 12 residues have shown significant antimicrobial activity (15). Previous reports from our laboratory have demonstrated antimicrobial activity of ⌬Phe-containing decapeptides (8).…”

Section: Discussionmentioning

confidence: 96%

“…In support of this, our results showed that a branched dimeric peptide, VSD1, exhibited excellent activity against E. coli (MIC, 1 M) and methicillin-resistant S. aureus (MIC, 5 M). Dewan et al, in their study on ⌬Phe-containing peptides, have shown that, along with increased antimicrobial properties, branched dimers show faster kill kinetics and increased serum stability compared to the linear dimeric analogs (8). Duplication of the vital antimicrobial structure in VSD1 resulted in very high antibacterial activity but simultaneously compromised its cell selectivity.…”

Section: Discussionmentioning

confidence: 99%

Rationale-Based, De Novo Design of Dehydrophenylalanine-Containing Antibiotic Peptides and Systematic Modification in Sequence for Enhanced Potency

Pathak

Chauhan

2011

Increased microbial drug resistance has generated a global requirement for new anti-infective agents. As part of an effort to develop new, low-molecular-mass peptide antibiotics, we used a rationale-based minimalist approach to design short, nonhemolytic, potent, and broad-spectrum antibiotic peptides with increased serum stability. These peptides were designed to attain an amphipathic structure in helical conformations. VS1 was used as the lead compound, and its properties were compared with three series of derivates obtained by (i) N-terminal amino acid addition, (ii) systematic Trp substitution, and (iii) peptide dendrimerization. The Trp substitution approach underlined the optimized sequence of VS2 in terms of potency, faster membrane permeation, and cost-effectiveness. VS2 (a variant of VS1 with two Trp substitutions) was found to exhibit good antimicrobial activity against both the Gram-negative Escherichia coli and the Gram-positive bacterium Staphylococcus aureus. It was also found to have noncytolytic activity and the ability to permeate and depolarize the bacterial membrane. Lysis of the bacterial cell wall and inner membrane by the peptide was confirmed by transmission electron microscopy. A combination of small size, the presence of unnatural amino acids, high antimicrobial activity, insignificant hemolysis, and proteolytic resistance provides fundamental information for the de novo design of an antimicrobial peptide useful for the management of infectious disease.

“…In the present study, our main aim was to determine the role of the amino acid sequences, particularly the contributions of N-terminal and C-terminal regions, in the staphylocidal mechanism of ␣-MSH. We selected four sequences of ␣-MSH, i.e., the entire ␣-MSH, ␣-MSH(1-5), ␣-MSH(6-13), and ␣-MSH (11)(12)(13), and studied in detail their antistaphylococcal activities against both MSSA and MRSA strains. The study was also extended to understand the effect of NaCl and different ions (Mg 2ϩ and Ca 2ϩ ) on the killing efficacy of peptides against S. aureus.…”

mentioning

confidence: 99%

C-Terminal Amino Acids of Alpha-Melanocyte-Stimulating Hormone Are Requisite for Its Antibacterial Activity against Staphylococcus aureus

Singh

Mukhopadhyay

2011

105

Alpha-melanocyte-stimulating hormone (␣-MSH) is an endogenous neuropeptide that is known for its anti-inflammatory and antipyretic activities.We recently demonstrated that ␣-MSH possesses staphylocidal activity and causes bacterial membrane damage. To understand the role of its amino acid sequences in the staphylocidal mechanism, in the present study we investigated the antimicrobial activities of different fragments of ␣-MSH, i.e., ␣-MSH(6-13), ␣-MSH(11-13), and ␣-MSH(1-5), and compared them with that of the entire peptide. Our results showed that peptides containing the C-terminal region of ␣-MSH, namely, ␣-MSH(6-13) and ␣-MSH(11-13), efficiently killed >90% of both methicillin-sensitive and -resistant Staphylococcus aureus cells in the micromolar range and ϳ50% of these cells in the nanomolar range; their efficiency was comparable to that of the entire ␣-MSH, whereas the peptide containing the N-terminal region, ␣-MSH(1-5), was found to be ineffective against S. aureus. The antimicrobial activity of ␣-MSH and its C-terminal fragments was not affected by the presence of NaCl or even divalent cations such as Ca 2؉ and Mg 2؉ . Similar to the case for the parent peptide, ␣-MSH(6-13) and ␣-MSH(11-13) also depolarized and permeabilized Staphylococcus cells (ϳ70 to 80% of the cells were depolarized and lysed after 2 h of peptide exposure at micromolar concentrations). Furthermore, scanning and transmission electron microscopy showed remarkable morphological and ultrastructural changes on S. aureus cell surface due to exposure to ␣-MSH-based peptides. Thus, our observations indicate that C-terminal fragments of ␣-MSH retain the antimicrobial activity of entire peptide and that their mechanism of action is similar to that of full-length peptide. These observations are important and are critical in the rational design of ␣-MSH-based therapeutics with optimal efficacy.