Improving the Activity of Trp-Rich Antimicrobial Peptides by Arg/Lys Substitutions and Changing the Length of Cationic Residues.

Mauricio Arias,Hans Vogel,Kathlyn Piga,M Hyndman

doi:10.3390/biom8020019

Mauricio Arias, Hans Vogel + Show 2 more

Open Access

https://doi.org/10.3390/biom8020019

Copy DOI

Abstract

Antimicrobial peptides (AMPs) constitute a promising alternative for the development of new antibiotics that could potentially counteract the growing number of antibiotic-resistant bacteria. However, the AMP structure–function relationships remain unclear and detailed studies are still necessary. The positively charged amino acid residues (Arg and Lys) play a crucial role in the activity of most AMPs due to the promotion of electrostatic interactions between the peptides and bacterial membranes. In this work we have analyzed the antimicrobial and structural properties of several Trp-rich AMPs containing exclusively either Arg or Lys as the positively charged residues. Their antimicrobial activity and mechanism of action were investigated, showing that Lys residues give rise to a reduced antimicrobial potency for most peptides, which was correlated, in turn, with a decrease in their ability to permeabilize the cytoplasmic membrane of Escherichia coli. Additionally, the presence of Arg and Lys renders the peptides susceptible to degradation by proteases, such as trypsin, limiting their therapeutic use. Therefore, modifications of the side chain length of Arg and Lys were investigated in an attempt to improve the protease resistance of AMPs. This approach resulted in enhanced stability to trypsin digestion, and in several cases, shorter sidechains conserved or even improved the antimicrobial activity. All together, these results suggest that Arg-to-Lys substitutions, coupled with side chain length modifications, can be extremely useful for improving the activity and stability of AMPs.

Highlights

Antimicrobial peptides (AMPs) are short amino acid sequences (5–50 residues) that are part of the innate immune systems of multicellular organisms, and they are involved in the protection of the host against infections by microorganisms [1,2,3,4]
Due to the dual role that Arg and Lys play in the activity and protease susceptibility of AMPs, we have focused in this work on the role of these cationic residues in the activity, mechanism of action, and proteolytic stability of a diverse group of Trp-rich AMPs
A diverse group of Trp-rich peptides was selected for this study in order to encompass a relatively broad group of AMPs (Table 1)

Summary

Introduction

Antimicrobial peptides (AMPs) are short amino acid sequences (5–50 residues) that are part of the innate immune systems of multicellular organisms, and they are involved in the protection of the host against infections by microorganisms [1,2,3,4]. The low stability of most peptides in biological fluids, such as serum or the gastrointestinal tract [13,14], is in part due to the susceptibility of AMPs to degradation by proteases Serine proteases such as trypsin are highly specific for Arg and Lys residues, while chymotrypsin recognizes aromatic residues (Trp, Phe, and Tyr). Modification of the side chain length of positively charged amino acids has been studied previously for specific AMPs, mainly in an attempt to promote proteolysis resistance against trypsin [13,15,20,21], in blood serum [17,18,19] or in whole organ extracts [13] These studies have shown that changes in the number of methylene groups of the side chain of Arg and Lys can result in increased resistance towards tryptic degradation

Methods

Results

Conclusion