Balancing hydrophobicity and sequence pattern to influence self‐assembly of amphipathic peptides

Abstract Amphipathic peptides with alternating polar and nonpolar amino acid sequences efficiently self‐assemble into functional β‐sheet fibrils as long as the nonpolar residues have sufficient hydrophobicity. For example, the Ac‐(FKFE) 2 ‐NH 2 peptide rapidly self‐assembles into β‐sheet bilayer nanoribbons, while Ac‐(AKAE) 2 ‐NH 2 fails to self‐assemble under similar conditions due to the significantly reduced hydrophobicity and β‐sheet propensity of Ala relative to Phe. Herein, we systematically explore the effect of substituting only two of the four Ala residues at various positions in the Ac‐(AKAE) 2 ‐NH 2 peptide with amino acids of increasing hydrophobicity, β‐sheet potential, and surface area (including Phe, 1‐naphthylalanine (1‐Nal), 2‐naphthylalanine (2‐Nal), cyclohexylalanine (Cha), and pentafluorophenylalanine (F 5 ‐Phe)) on the self‐assembly propensity of the resulting sequences. It was found that double Phe variants, regardless of the position of substitution, failed to self‐assemble under the conditions used in this study. In contrast, all double 1‐Nal and 2‐Nal variants readily self‐assembled, albeit at differing rates depending on the substitution patterns. To determine whether this was due to hydrophobicity or side chain surface area, we also prepared double Cha and F 5 ‐Phe variant peptides (both side chain groups are more hydrophobic than Phe). Each of these variants also underwent effective self‐assembly, with the aromatic F 5 ‐Phe peptides doing so with greater efficiency. These findings provide insight into the role of amino acid hydrophobicity and sequence pattern on self‐assembly proclivity of amphipathic peptides and on how targeted substitutions of nonpolar residues in these sequences can be exploited to tune the characteristics of the resulting self‐assembled materials.