The Effect of Selective D- or Nα-Methyl Arginine Substitution on the Activity of the Proline-Rich Antimicrobial Peptide, Chex1-Arg20

Abstract

<i>In vivo</i> pharmacokinetics studies have shown that the proline-rich antimicrobial peptide, A3-APO, which is a discontinuous dimer of the peptide, Chex1-Arg20, undergoes degradation to small fragments at positions Pro6-Arg7 and Val19-Arg20. With the aim of minimizing or abolishing this degradation, a series of Chex1-Arg20 analogs were prepared <i>via</i> Fmoc/tBu solid phase peptide synthesis with D-arginine or, in some cases, peptide backbone N^α-methylated arginine, substitution at these sites. All the peptides were tested for antibacterial activity against the Gram-negative bacterium <i>Klebsiella pneumoniae</i>. The resulting activity of position-7 substitution of Chex1-Arg20 analogs showed that arginine-7 is a crucial residue for maintaining activity against <i>K. pneumoniae</i>. However, arginine-20 substitution had a much less deleterious effect on the antibacterial activity of the peptide. Moreover, none of these peptides displayed any cytotoxicity to HEK and H-4-II-E mammalian cells. These results will aid the development of more effective and stable PrAMPs <i>via</i> judicious amino acid substitutions.