ABSTRACT Most antimicrobial peptides (AMPs) are cationic, with positively charged amino acid residues (i.e., arginine, lysine, and/or histidine) being responsible for their selective interaction with bacteria. In the present study, we investigated the influence of the nature of cationic residues taking the Lynronnes peptides as models. Derivatives were designed and synthetized with substitutions of the type of cationic residues present. All derivatives and parental peptides were studied in terms of secondary structure, antimicrobial activity, anti‐biofilm activity, mechanism of action, and in vitro toxicity. All‐His peptides were found inactive, whereas all‐Lys variants showed the highest potency against Gram‐negative strains, particularly against E. coli . All‐Arg analogues were more active against Gram‐positive strains with enhanced stability under salt or serum conditions but were also more hemolytic. Mechanistic studies revealed that the peptides act by membrane permeabilization. Finally, Lynronne‐3 and its all‐Lys derivative proved the most effective in both the prevention and eradication of biofilms. These findings confirm that the type of cationic residue present in AMPs affects their activity, toxicity, and sensitivity to host factors, with different effects depending on the rest of the amino acid sequence, Lys‐substitution emerging as a promising strategy in the case of Lynronnes for targeting E. coli .
ABSTRACT The global spread of antimicrobial resistance, particularly among clinically important Gram‐negative pathogens, has intensified the search for effectives to conventional antibiotics. Antimicrobial peptides are promising, as they act rapidly on bacterial envelopes and may circumvent resistance. Here, we rationally designed two derivatives of MAP 34‐B, MAP 34B‐1, and MAP 34B‐2 and comparatively evaluated their antibacterial activity, physicochemical stability, membrane‐associated mechanism, and cytocompatibility. MAP 34B‐1 displayed stronger and broader activity against Escherichia coli and Acinetobacter baumannii than MAP 34B‐2 and rapidly reduced bacterial viability within 2 h. In contrast, MAP 34B‐2 exhibited a narrower antibacterial spectrum and weaker activity against A. baumannii . Scanning electron microscopy revealed morphological damage of bacterial cells, FITC‐labeled peptide localization confirmed membrane binding, and membrane permeability assays demonstrated disruption of membrane integrity. Collectively, these results support a membrane‐associated antibacterial mechanism for MAP 34B‐1. Both derivatives retained antibacterial activity under the tested salt and thermal conditions. Notably, MAP 34B‐1 caused less mammalian‐cell cytotoxicity and hemolysis than MAP 34B‐2, resulting in a more favorable balance between antibacterial potency and host‐cell compatibility. Overall, these findings demonstrate that rational sequence optimization of MAP 34‐B can substantially modulate antibacterial spectrum, membrane activity, and biocompatibility. MAP 34B‐1 therefore represents a promising lead peptide for further development against infections caused by E. coli and A. baumannii .
Two complementary series of novel tryptophan-derived dipeptides (Trp-X and X-Trp) were designed and synthesized to systematically evaluate how backbone sequence inversion alters chemical accessibility and in vitro antineoplastic profiles against a human solid tumor cell line panel (A549, HeLa, MIA PaCa-2, SW1573, T-47D, and WiDr). Reversing the peptide connectivity revealed prominent sequence-dependent chemical reactivities and biological variations. Steric repulsion at the beta-carbon limited basic hydrolysis during X-Trp precursor assembly, whereas the Trp-X series allowed straightforward chemical couplings. Phenotypic screening demonstrated that the Trp-X configuration is biologically superior to the X-Trp layout. The conformationally restricted L-proline conjugate (Trp-Pro) emerged as the lead architecture, exhibiting consistent, single-digit sub-micromolar growth inhibition across all histotypes (GI50 = 1.36-2.06 mu M) and effectively outperforming clinical standards cisplatin and 5-fluorouracil in resistant models. Interestingly, an inversion of structure-activity relationships was observed in the reverse series, where specific residues like L-phenylglycine and L-tyrosine experienced a prominent rescue of potency upon sequence relocation. These results confirm that the antiproliferative profile of these peptidomimetics is strictly dictated by a highly directional, sequence-specific molecular topology rather than aggregate lipophilicity alone.
ABSTRACT We screened for anti‐ice‐nucleation peptides using the phage display library method, with silver iodide as the target for artificial ice nucleation The phage interacted with the silver iodide in a dispersed state, rather than in an immobilized state. Based on DNA analysis, we identified five peptides with high expression levels. Five peptide sequences were synthesized by hand using the Fmoc solid‐phase peptide synthesis and evaluated their anti‐ice‐nucleation activity. Three peptide sequences exhibited anti‐ice‐nucleation activity, and two of them were insoluble in water. Among the three peptides, SHIARSV exhibited the highest anti‐ice‐nucleation activity. To determine the importance of each amino acid in SHIARSV, we designed five peptides in which Ala was substituted and examined their anti‐ice‐nucleation activity. As a result, we identified AHIARSV, a peptide sequence with higher anti‐ice‐nucleation activity than the original SHIARSV sequence. This peptide exhibited high levels of both anti‐nucleation activity and ice recrystallization inhibition activity. It is our conclusion that the design of antifreeze peptides with activities comparable with those of natural ones is highly feasible.
