Identification of antibacterial peptides from ovine αs2-casein

The aim of this work was to isolate and identify antibacterial peptides present in a pepsin digest of ovine αs2-casein. A protein digest with antibacterial properties was first separated by ion exchange chromatography. The fractions most active against Escherichia coli ATCC 25922 were fractionated by semi-preparative RP-HPLC, and the identification of the active peptides was carried out by on-line and off-line RP-HPLC-ESI-MS/MS. Following this strategy, 10 different peptides were identified, all corresponding to the C-terminal region of the ovine αs2-casein. Four of them were chemically synthesized and showed antibacterial activity against several Gram-positive and Gram-negative bacteria. Among the synthesized peptides, ovine αs2-casein f(165–181) exhibited the highest antibacterial potency against all bacteria tested. The antimicrobial activity was compared with that of other previously described peptides like lactoferricin and fragment f(183–207) of bovine αs2-casein.