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A hybrid cationic peptide composed of human beta-defensin-1 and humanized theta-defensin sequences exhibits salt-resistant antimicrobial activity.  Olli S, Nagaraj R, Motukupally SR., Antimicrob. Agents Chemother., 2014, Oct 27. [Epub ahead of print]

We have designed a hybrid peptide by combining sequences of human β-defensin-1 and θ-defensin, in an attempt to generate a molecule that combines the diversity in structure and biological activity of two different peptides to yield a promising therapeutic candidate. HBD-1 was chosen as it is a natural defensin of humans that is constitutively expressed but its antibacterial activity is considerably impaired by elevated ionic strength. θ-defensins are expressed in the human bone marrow as a pseudogene that are homologous to rhesus monkey circular minidefensins. Retrocyclins are synthetic human θ-defensins. The cyclic nature of the θ-defensin peptides makes them salt resistant, non-hemolytic, and virtually non-cytotoxic in vitro. However, developing a non-human circular molecule for clinical use would be less viable as compared to a linear molecule. In this study, we have fused the C-terminal region of HBD-1 to the nonapeptide sequence of a synthetic retrocyclin. Cyclization was achieved by joining the terminal ends of the hybrid peptide by a disulfide bridge. The hybrid peptide exhibited enhanced antimicrobial activity with or without the disulfide bridge against both Gram-negative and Gram-positive bacteria as well as against fungi, including clinical bacterial isolates from eye infections. The peptide retained activity in the presence of NaCl and serum and was non-hemolytic in vitro. Thus, the hybrid peptide  generated holds potential as a new class of antibiotics.

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