Role of helicity of α-helical antimicrobial peptides to improve specificity

Abstract

A major barrier to the use of antimicrobial peptides as antibiotics is the toxicity or ability to lyse eukaryotic cells. In this study, a 26-residue amphipathic α-helical antimicrobial peptide A12L/A20L (Ac-KWKSFLKTFKSLKKTVLHTLLKAISS-amide) was used as the framework to design a series of D- and L-diastereomeric peptides and study the relationships of helicity and biological activities of α-helical antimicrobial peptides. Peptide helicity was measured by circular dichroism spectroscopy and demonstrated to correlate with the hydrophobicity of peptides and the numbers of D-amino acid substitutions. Therapeutic index was used to evaluate the selectivity of peptides against prokaryotic cells. By introducing D-amino acids to replace the original L-amino acids on the non-polar face or the polar face of the helix, the hemolytic activity of peptide analogs have been significantly reduced. Compared to the parent peptide, the therapeutic indices were improved of 44-fold and 22-fold against Gram-negative and Gram-positive bacteria, respectively. In addition, D- and L-diastereomeric peptides exhibited lower interaction with zwitterionic eukaryotic membrane and showed the significant membrane damaging effect to bacterial cells. Helicity was proved to play a crucial role on peptide specificity and biological activities. By simply replacing the hydrophobic or the hydrophilic amino acid residues on the non-polar or the polar face of these amphipathic derivatives of the parent peptide with D-amino acids, we demonstrated that this method could have excellent potential for the rational design of antimicrobial peptides with enhanced specificity.

pH Dependent Antimicrobial Peptides and Proteins, Their Mechanisms of Action and Potential as Therapeutic Agents

“…Low pH was found to enhance the activity of both peptides against Escherichia coli , which appeared to involve membrane interaction, but interestingly, although gad-1 and gad-2 were predominantly α-helical at neutral pH, acid conditions led to a large decrease in the levels of α-helicity possessed by these peptides [29]. These results contrast with most α-helical AMPs where an enhanced capacity for membranolysis and antimicrobial activity is generally associated with increased levels of this secondary structure [96,97]. It was proposed that gad-1 and gad-2 each possessed a structural plasticity, which facilitated an appropriate balance between amphiphilic and mixed hydrophobic/hydrophilic structural features that promoted maximal levels of membrane interaction and antibacterial activity [29].…”

Binary Encoding of Random Peptide Sequences for Selective and Differential Antimicrobial Mechanisms

“…[10] Mimicking AMPs with unnatural oligomers [11] can provide artificial analogues that exhibit similar activities with ah igher enzymatic stability and disfavored oligomerization capacities. [16] Current evidence suggests that single l-to-d mutations in all-l sequences lead to decreased helicity and decreased hemolytic activities without affecting the antimicrobial properties. [13,14] An effective solution to these issues may be found in peptide diastereomers, [15] which are commonly used to explore the dependence of biological activities on a-helix formation.…”

Sequence Analysis and Modeling of Antimicrobial Peptide from Goat Milk Protein Hydrolyzed by Bromelain

“…HC50 value is the mean concentration of peptide producing 50% hemolysis of freshly isolated human erythrocytes from healthy donors, while MIC is defined as the minimum inhibitory concentration using the microdilution susceptibility test against Escherichia coli. Larger value in therapeutic index indicate greater antimicrobial specificity (Huang et al 2014) that means high in bacteriostatic activity and low in toxicity (Juretic et al 2009a). Therapeutic index value is able to be obtained from experiment (experimental therapeutic index; TIexp) or from software prediction (therapeutic index prediction, TIpred) (Kamech et al 2012).…”

“…Multiple studies demonstrated that helicity is important for toxicity, antimicrobial activity (Huang et al 2010) and interfacial binding (Fernandez-Vidal 2007) beside physicochemical parameter such as hydrophobicity amphipaticity, charge and sequence also determine antimicrobial activity. It is important in interaction between peptide and microbial membrane (Huang et al 2014).…”