Penetration of Milk-Derived Antimicrobial Peptides into Phospholipid Monolayers as Model Biomembranes

Table 1

Data on structure and antimicrobial activities of the investigated peptides.

Name	Origin/molecular mass	Amino acid sequence	Total net charge at pH 7/pH 5.6^(a, e)	Total hydrophobic ratio [%]^(a)	No. of hydrophobic residues on molecule surface/all residues^(a)	Secondary structure	IEP predicted	Antimicrobial and hemolytic activities
E-5-K	Residues 1–5 of α-lactalbumin/689 g/mol	H2N-EQLTK-COOH	0/ca. 0^(b)	20	0/1	Random coil or quasi-pure β-sheet^(c) [26]	6.1 [26]; 6.9 [35]	G. + bacteria; Not fungicidal [26]
L-16-Y	Residues 164–179 of α-casein/2011.4 Da	H2N-LKKISQRYQKFALPQY-COOH	+4/+4	31	0/5	Random coil [35] or α-helix^(c, e) [31, 35]	10.5 [35]	G. + and G. − bacteria; Slightly hemolytic [31]
N-23-T or Lactophoricin-I (LPcin-I)	Residues 113–135 of bovine component-3 of proteose peptone (PP3)/2683 Da	H2N-NTVKETIKYLKSLFSHAFEVVKT-COOH	+2.1/+3	39	9/9	α-helix^(c) [32], random in solutions and 50% helical content in LPC^(d) and SDS^(d) micelles [33], monomer in H2O [32]	9.4 [33]; 9.95^(e)	Mostly against G. + bacteria,; not hemolytic [32]

(a)Values predicted using the “APD2: Antimicrobial Peptide Predictor” software, available at http://aps.unmc.edu/AP/main.php [3].
(b)According to the theoretical prediction of IEP of E-5-K (consistent with [26, 35]), this peptide should adopt a slightly positive charge at the used pH ca. 5.6; however, the penetration results (Figure 8) indicate a slight negative charge of E-5-K, under the experimental conditions.
(c)Derived according to the secondary structure algorithm [31].
(d)LPC denotes L-α-lysophosphatidylcholine, and SDS denotes sodium dodecyl sulphate.
(e)The value is predicted using the “Peptide Property Calculator” of CS Bio Co. software available at http://pepcalc.com/ppc.php (used also in [35]).