Synthetic bovine NK-lysin-derived peptide (bNK2A) does not require intra-chain disulfide bonds for bactericidal activity

Bovine NK-lysins are cationic antimicrobial proteins found predominantly in the cytosolic granules of T lymphocytes and NK-cells. NK-lysin-derived peptides show antimicrobial activity against both Gram positive and Gram negative bacteria. Mature NK-lysin protein has six well-conserved cysteine residues. This study was performed to assess whether synthetic bovine NK-lysin-derived peptide (bNK2A) forms disulfide bonds and whether disulfide bonds were essential for bNK2A antimicrobial activity. Two 30-mer bNK2A peptides were synthesized: one with two original cysteines and an analog with cysteines substituted with two serines. Mass spectrometry revealed lack of disulfide bonds in original peptide while CD spectrophotometry showed both peptides have similar α-helical structures. Since both peptides were equally inhibitory to Histophilus somni, disulfide bonds appeared dispensable for synthetic bNK2A peptide antibacterial activity.