Extensive Manipulation of Caseicins A and B Highlights the Tolerance of These Antimicrobial Peptides to Change

Abstract

Caseicins A and B are low-molecular-weight antimicrobial peptides which are released by proteolytic digestion of sodium caseinate. Caseicin A (IKHQGLPQE) is a nine-amino-acid cationic peptide, and caseicin B (VLNENLLR) is a neutral eight-aminoacid peptide; both have previously been shown to exhibit antibacterial activity against a number of pathogens, including Cronobacter sakazakii. Previously, four variants of each caseicin which differed subtly from their natural counterparts were generated by peptide synthesis. Antimicrobial activity assays revealed that the importance of a number of the residues within the peptides was dependent on the strain being targeted. In this study, this engineering-based approach was expanded through the creation of a larger collection of 26 peptides which are altered in a variety of ways. The investigation highlights the generally greater tolerance of caseicin B to change, the fact that changes have a more detrimental impact on anti-Gram-negative activity, and the surprising number of variants which exhibit enhanced activity against Staphylococcus aureus.

Structure-Activity Relationship of Synthetic Variants of the Milk-Derived Antimicrobial Peptide α s2 -Casein f(183–207)

“…In order to assess the overall impact of variant changes on the antimicrobial activity of the ␣ s2 -casein f(193-207) peptide, each peptide variant was assigned an arbitrary activity unit (AAU) value reflecting its MIC relative to that of the corresponding wild-type peptide. These values were as follows: 0, at least 8-fold-reduced activity; 1, 4-fold-reduced activity; 2, 2-fold-reduced activity; 3, wild-type activity; 4, 2-fold-increased activity; 5, 4-fold-increased activity; 6, Ն8-fold-increased activity (15).…”

“…Template-based studies of peptide derivatives obtained through manipulation of the amino acid sequence have often been performed in order to identify properties that are important for AMP activity (12). Such studies have shed light on the importance of specific amino acids and residue positions in the activities of different peptides (13)(14)(15). However, it appears that the effect of particular manipulations is context dependent and varies according to the template sequence, in that analogous substitutions may have substantially different effects on different peptides or at different positions in the primary sequence (16).…”

Structure-Activity Relations of Myxinidin, an Antibacterial Peptide Derived from the Epidermal Mucus of Hagfish

“…Thus, to overcome the limitations of native peptides, peptidomimetics have become an important and promising approach. Many AMPs can be optimized to enhance their effectiveness and stability through modification of their sequences, making them good templates for the development of therapeutic agents (16)(17)(18). Bioinformatics has recently helped in developing and/or modifying preexisting AMPs, driving their synthesis toward more effective and selective drugs.…”