A recipe for designing water‐soluble, β‐sheet‐forming peptides

Based on observations of solubility and folding properties of peptide 33‐mers derived from the β‐sheet domains of platelet factor‐4 (PF4), interleukin‐8 (IL‐8), and growth related protein (Gro‐α), as well as other β‐sheet‐forming peptides, general guidelines have been developed to aid in the design of water soluble, self‐association‐induced β‐sheet‐forming peptides. CD, 1 H‐NMR, and pulsed field gradient NMR self‐diffusion measurements have been used to assess the degree of folding and state of aggregation. PF4 peptide forms native‐like β‐sheet tetramers and is sparingly soluble above pH 6. IL‐8 peptide is insoluble between pH 4.5 and pH 7.5, yet forms stable, nativelike β‐sheet dimers at higher pH. Gro‐α peptide is soluble at all pH values, yet displays no discernable β‐sheet structure even when diffusion data indicate dimer‐tetramer aggregation. A recipe used in the de novo design of water‐soluble β‐sheet‐forming peptides calls for the peptide to contain 40‐50% hydrophobic residues, usually aliphatic ones (I, L, V, A, M) (appropriately paired and mostly but not always alternating with polar residues in the sheet sequence), a positively charged (K, R) to negatively charged (E, D) residue ratio between 4/2 and 6/2, and a noneharged polar residue (N, Q, T, S) composition of about 20% or less. Results on four de novo designed, 33‐residue peptides are presented supporting this approach. Under near physiologic conditions, all four peptides are soluble, form β‐sheet structures to varying degrees, and self‐associate. One peptide folds as a stable, compact β‐sheet tetramer, whereas the others are transient β‐sheet‐containing aggregates.