A hybrid cationic peptide composed of human beta - defensin - 1 and 1 humanized theta - defensin sequences exhibits salt - resistant 2 antimicrobial activity

20 We have designed a hybrid peptide by combining sequences of human β-defensin-1 and 21 θ-defensin, in an attempt to generate a molecule that combines the diversity in structure and 22 biological activity of two different peptides to yield a promising therapeutic candidate. HBD-1 23 was chosen as it is a natural defensin of humans that is constitutively expressed but its 24 antibacterial activity is considerably impaired by elevated ionic strength. θ-defensins are 25 expressed in the human bone marrow as a pseudogene that are homologous to rhesus monkey 26 circular minidefensins. Retrocyclins are synthetic human θ-defensins. The cyclic nature of the θ27 defensin peptides makes them salt resistant, non-hemolytic, and virtually non-cytotoxic in vitro. 28 However, developing a non-human circular molecule for clinical use would be less viable as 29 compared to a linear molecule. In this study, we have fused the C-terminal region of HBD-1 to 30 the nonapeptide sequence of a synthetic retrocyclin. Cyclization was achieved by joining the 31 terminal ends of the hybrid peptide by a disulfide bridge. The hybrid peptide exhibited enhanced 32 antimicrobial activity with or without the disulfide bridge against both Gram-negative and Gram33 positive bacteria as well as against fungi, including clinical bacterial isolates from eye infections. 34 The peptide retained activity in the presence of NaCl and serum and was non-hemolytic in vitro. 35 Thus, the hybrid peptide generated holds potential as a new class of antibiotics. 36