Identification of three novel ostricacins: an update on the phylogenetic perspective of β-defensins

Three new β-defensins, ostricacins-2, 3 and 4 (Osp-2, 3 and 4), have been successfully purified and characterised from ostrich heterophils in addition to ostricacin-1 (Osp-1). These peptides are composed of 36–42 amino acids with a molecular weight range of 4.70–4.98 kDa. In vitro, Osp-1, 3 and 4 were active against Escherichia coli O157:H7 and Staphylococcus aureus 1056 MRSA, whilst Osp-2 was active against bacterial strains plus the yeast Candida albicans 3153A. Minimal inhibitory concentrations of the three ostricacins ranged from 0.96 μg/mL to 12.03 μg/mL. Comparison with the known β-defensins from mammalian and other avian species revealed that the four ostricacins shared eight conserved residues (six cysteines and two glycines), identified as the ‘β-defensin core motif’. Comparisons of the sequence also indicated that β-defensins could have originated from a common β-defensin-like ancestor that occurred before avian and mammalian lines diverged.