Full Paper Production of bioactive human α-defensin 5 in Pichia pastoris

Defensins are a well characterized family of antimicrobial peptides that are divided into two main classes, the αand β-defensins, based on the pairing pattern of disulphide bonds (Ganz, 2003; Yang et al., 2004). In humans, the respective genes of the two major classes (α and β) are clustered on the short arm of chromosome 8 (Harder et al., 1997; Liu et al., 1997). The human genome project suggests the presence of more than 20 defensin-related genes (Schutte et al., 2002). Human α-defensin 5 (HD5) is an arginine-rich small cationic peptide (29‒35 amino acid residues) ranging from 3.5 to 4 kDa in size with six cysteines forming three intramolecular disulfi de bonds. HD5 has a broad spectrum of antimicrobial activity in vitro, and is active against a variety of bacteria, fungi, parasites and some viruses (Ganz, 2003). HD5 peptide kills bacteria by binding electrostatically to the negatively charged membranes and forming pores within the bacterial cell membrane to further result in cell lysis (Zasloff, 2002). Unlike other characterized defensins, HD5 is stored in secretory vesicles as a propeptide and further processed to be a fully active form. HD5 is stored in the ileal mucosa at concentrations of 90‒450 μg per cm2 of mucosal surface area, and is suffi cient to generate microbicidal concentrations in the intestinal lumen (Ghosh et al., 2002). HD5 peptides isolated from the J. Gen. Appl. Microbiol., 55, 395‒401 (2009)