Biological activities and structural properties of the atypical bacteriocins mesenterocin 52b and leucocin b-ta33a

Abstract

The antibacterial spectra and modes of action of synthetic peptides corresponding to mesenterocin 52B and leucocin B-TA33a greatly differ despite their high sequence homology. Circular dichroism experiments establish the capacity of each of these two peptides to partly fold into an amphiphilic helix that might be crucial for their adsorption at lipophilic-hydrophilic interfaces.

FIG. 1

Kinetics of death of W. paramesenteroides LMA 19 cells (A) and L. pseudomesenteroides CIP 103316 cells (B) in MRS broth at 30°C. ○, control; ■, mesenterocin 52B (0.03 mg/ml); ▴, leucocin B-TA33a (0.03 mg/ml).

FIG. 2

Effect of SDS on the CD spectra of leucocin B-TA33a and mesentorocin 52B in aqueous solution. The spectra of the two peptides (24 μM in 20 mM phosphate buffer, pH 7) were recorded in the absence or in the presence of various amounts of SDS. (A) Leucocin B-TA33a. Concentrations of SDS were as follows: none (●), 5 μM (■), 10 μM (▴), 30 μM (▵), and 10 mM (+). (B) Mesenterocin 52B. SDS concentrations were as follows: none (●), 20 μM (■), 50 μM (▴), 0.2 mM (▵), and 20 mM (+).

FIG. 3

Effect of TTAB on the CD spectra of mesenterocin 52B in aqueous solution (24 μM peptide, 10 mM phosphate, pH 7). The spectra were recorded in the wavelength range of 180 to 250 nm except for the highest concentrations of TTAB (205 to 252 nm) because of the strong absorption of this compound at short wavelengths. TTAB concentrations were as follows: none (●), 1 mM (■), 2 mM (▴), 4 mM (▵), and 10 mM (+).

FIG. 4

CD spectra of mesenterocin 52B in aqueous solution (24 μM peptide, 10 mM phosphate, pH 7) at the following LPC concentrations: none (●), 0.6 mM (■), 1 mM (▴), 2mM (▵), and 3.3 mM (+).

FIG. 5

Edmunsen α-helical wheel representation of the amphiphilic region of leucocin B-T33a (A) and mesenterocin 52B (B). The amphiphilic region starts with residue 3 and ends with residue 17 in the leucocin B-T33a sequence, whereas it starts with residue 1 and ends with residue 15 for mesenterocin B52. The boxes denote hydrophobic residues.