adhesin-derived peptides mediate strong pull-off forces in aqueous media with high ionic strength

In this study, the pull-off forces of adsorbed films of four Bap1-inspired peptides in various solvents were investigated on negatively charged mica substrates using the surface forces apparatus (SFA), complemented with dynamic light scattering (DLS) for characterizing the aggregation behavior of peptides in solution. Bap1-inspired peptides consisted of the 57 amino acid wild-type sequence (WT); a scrambled version of the WT used to investigate the impact of the primary amino acid sequence in pull-off forces (Scr); a ten amino acid sequence rich in hydrophobic content (CP) of the WT sequence, and an eight amino acid sequence (Sh1) that corresponds to the pseudo-repeating sequence in the 57 AA. SFA results showed remarkable pull-off forces for CP, particularly in the presence of salts: measured pull-off forces were 26.0 ± 7.0 mN/m for no dwell-time and up to 42.0 ± 8.8 mN/m when surfaces were left in contact for 30 min. Sh1 did not bridge mica surfaces, while large aggregates clouded SFA measurements of Scr. DLS observations indicated that salts favored large peptide aggregation for all constructs (D_H > 1 µm), as compared to milliQ (D_H ≈ 100-500 nm) water and DMSO (D_H ≈ 5 nm), resulting in heterogeneous peptide film thicknesses.