Helix induction potential of N-terminal α-methyl, α-amino acids

University of Padova
Letters in Peptide Science 04/1998; 5(2):105-107. DOI: 10.1023/A:1008873910529

ABSTRACT A series of longer analogues of the C-peptide of RNAse A has been synthesized with the aim of assessing the helix induction potential in water of -methyl, -amino acids at the N-terminus of the chain. The circular dichroism data indicate that one isovaline residue is effective in increasing the helix content of the 13-residue peptide by about 7%.

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    ABSTRACT: We have analysed the toxicity of highly cationic, artificial alpha-helical antimicrobial peptides on blood cells to assess their suitability for systemic application. Flow cytometric methods, based on the uptake of propidium iodide, were used to obtain a rapid and quantitative estimate of membrane damage to resting and concanavalin A-activated mouse lymphocytes, which was further confirmed by morphological changes as observed by scanning electron microscopy. Membrane permeabilization appeared to correlate with structural characteristics, so that the peptide L-19(9/B), which contains helix-stabilizing aminoisobutyric acid (Aib) residues and is a potent antimicrobial, was also the most lytic towards both mouse lymphocytes and human erythrocytes. Reducing the propensity for helix formation in P19(8) resulted in a marked reduction in in vitro cytotoxicity. Changing the helical sense in D-P19(9/B) also resulted in a significant decrease in cytolytic activity towards both erythrocytes and leucocytes. A limited assessment in BALB/c mice confirmed a lower in vivo toxicity of P19(8) than L-P19(9/B). In a study of the systemic antimycotic activity of P19(8) in a mouse protection model, a modest prolongation in survival of Candida albicans-infected animals after intravenous administration was observed at 5 mg/kg peptide but not at higher doses. The implications of these observations for the systemic use of this type of peptide are discussed.
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