Cationic antimicrobial peptides (CAMPs) are a promising alternative to treat multidrug-resistant bacteria, which have developed resistance to all the commonly used antimicrobial, and therefore represent a serious threat to human health. One of the major drawbacks of CAMPs is their sensitivity to proteases, which drastically limits their half-life. Here we describe the design and synthesis of three nine-residue CAMPs, which showed high stability in serum and broad spectrum antimicrobial activity. As for all peptides a very low selectivity between bacterial and eukaryotic cells was observed, we performed a detailed biophysical characterization of the interaction of one of these peptides with liposomes mimicking bacterial and eukaryotic membranes. Our results show a surface binding on the DPPC/DPPG vesicles, coupled with lipid domain formation, and, above a threshold concentration, a deep insertion into the bilayer hydrophobic core. On the contrary, mainly surface binding of the peptide on the DPPC bilayer was observed. These observed differences in the peptide interaction with the two model membranes suggest a divergence in the mechanisms responsible for the antimicrobial activity and for the observed high toxicity toward mammalian cell lines. These results could represent an important contribution to unravel some open and unresolved issues in the development of synthetic CAMPs.

Antimicrobial peptides are promising candidates as future therapeutics in order to face the problem of antibiotic resistance caused by pathogenic bacteria. Myxinidin is a peptide derived from the hagfish mucus displaying activity against a broad range of bacteria. We have focused our studies on the physico-chemical characterization of the interaction of myxinidin and its mutant WMR, which contains a tryptophan residue at the N-terminus and four additional positive charges, with two model biological membranes (DOPE/DOPG 80/20 and DOPE/DOPG/CL 65/23/12), mimicking respectively Escherichia coli and Pseudomonas aeruginosa membrane bilayers. All our results have coherently shown that, although both myxinidin and WMR interact with the two membranes, their effect on membrane microstructure and stability are different. We further have shown that the presence of cardiolipin plays a key role in the WMR-membrane interaction. Particularly, WMR drastically perturbs the DOPE/DOPG/CL membrane stability inducing a segregation of anionic lipids. On the contrary, myxinidin is not able to significantly perturb the DOPE/DOPG/CL bilayer whereas interacts better with the DOPE/DOPG bilayer causing a significant perturbing effect of the lipid acyl chains. These findings are fully consistent with the reported greater antimicrobial activity of WMR against P. aeruginosa compared with myxinidin.

The stability of two thermophilic esterases, AFEST from Archaeoglobus fulgidus and EST2 from Alicyclobacillus acidocaldarius, against the denaturing action of urea and guanidine hydrochloride has been investigated by means of steady-state fluorescence and circular dichroism measurements. Experimental results indicate that the two enzymes, even though very resistant to temperature and urea, show a resistance to guanidine hydrochloride weaker than expected on the basis of data collected so far for a large set of globular proteins. Structural information available for AFEST and EST2 and ideas that emerged from studies on the molecular origin of the greater thermal stability of thermophiles allow the suggestion of a reliable rationale. The present results may be an indication that the optimization of charge—charge interactions on the protein surface is a key factor for the stability of the two esterases.

The interaction in water of ethanol, n-propanol, n-butanol, isobutanol, s-butanol and t-butanol with α-cyclodextrin (hexacycloamylose, αCD) has been studied calorimetrically at 298.15 K. The results indicate that, with the exception of the t-butanol, these alcohols form inclusion complexes with this dextrin. The calorimetric method employed allows the determination of the thermodynamic parameters characterizing the binding process, namely the enthalpy, ΔH_B°, the apparent equilibrium constant,K′_B, and then the free energy, ΔG_B°′, and entropy, TΔS_B°′. The complexes that result are weak, as shown by the low values of the constants. The absolute values of ΔH_B° and K′_B increase with increasing length of the alkyl chain. Branching of the alkyl chain lowers the value of K′_B. Evidence is given to show that t-butanol does not form a complex with αCD, probably because of steric hindrance: for this system the calorimetric data are treated according to an approach derived from the McMillan–Mayer treatment of solutions.