Vibrational study of auto-assembling oligopeptides for biomedical applications

Eight alternating polar/non-polar peptides derived from β-sheet EAK-16 were studied for their possible use as biomimetic materials, due to their self-assembling properties. IR and Raman spectroscopies were used to investigate the influence of the sequence on the prevailing conformation of the peptide and its changes after solubilisation in saline phosphate buffer and lyophilisation. As regards the as-synthesised peptides, acidic substitution (Glu → Asp, peptide 2), basic substitution (Lys → Orn, peptide 3), (Glu → Asp and Lys → Orn, peptide 4) and spacer substitution (Ala → Abu, peptide 5; Ala → Tyr, peptide 6) did not induce significant conformational changes with respect to EAK-16 (peptide 1); the prevailing structure was β-sheet (about 70%), with about 15% of β-turn, 10% of unordered structure and a minor α-helix content. The insertion at the N-terminus of the Arg-Gly-Asp sequence (peptide 7), important for cell adhesion, induced a decrease in the β-sheet content (50%), while the simultaneous ‘scrambling’ of the sequence (peptide 8) made α-helix the prevailing structure. Solubilisation/lyophilisation procedures generally induced a change towards a less ordered conformation in all the analysed peptides. However, for peptides 1–7, the prevailing conformation remained β-sheet. Peptide 8 was prevalently unordered with a lower β-sheet content.