metal-binding ß-hairpin peptides

Summary Hydrogel materials are used in tissue engineering,1-3 microfluidics,4,5 and drug delivery.6,7 A promising approach for the design of hydrogels is the use of self-assembling peptides in which noncovalent interactions between molecules drive the assembly and formation of supramolecular fibril networks that define the material.8-10 Using peptides as building blocks, one can form self-assembled structures that result in a percolated hydrogel network.

Zinc is an essential cofactor in many cell processes, promotes wound repair and has an anti-bacterial effect. 11-15 Therefore, formation of hydrogels by the self-assembly of zinc-binding peptides could be highly beneficial for tissue engineering and other biomedical applications.

In this proposal grant we succeeded to design several novel zinc-binding β-hairpin peptides that demonstrate stable self-assembling fibrils. The self-assembly of these novel designed peptides can be applied to the formation of new hydrogel materials for biomedical applications.

We have used the amphiphilic MAX1 β-hairpin peptide that has been designed previously by the American PI (Figure 1).

/ We mutated hydrophobic residues and hydrophilic residues along the β-strands of MAX1 by residues Cys and His that can bind zinc ions. Table 1 illustrates the mutations that we performed in MAX1 sequence.

Table 1: Sequences of the designed β-hairpin peptides. Residues that are colored in red are metal-binding mutations of MAX1. Light orange background represents mutations in the hydrophobic region of the peptide; Light blue background represents mutations in the hydrophilic region of the peptide.

We applied molecular modeling tools to construct the self-assembly of the zinc-peptide complexes by forming fibril-like structures, considering four possible organization between the two layers (Figure 2). We then applied molecular dynamics (MD) simulations and various analysis tools to investigate the stability of the simulated fibril-like structures.

/ Figure 3 illustrates one of the simulated fibril-like structural models, in which the two Val residues (Val1 and Val20) were mutated by two His residues and zinc ions bind four His residues: two His residues in each layer. This structural model is organized in conformer 3 (as illustrated in Figure 2).

Our results led us to conclude that mutations of the hydrophobic Val20 residue by His prefers to organized in conformer 3 (as seen in Figure3), but mutations of the hydrophobic Val20 residue by Cys prefers to organize in conformer 1. We also found that mutations of the hydrophilic residues (Lys) in MAX1 to His yield to stable fibril-like structures, while mutations to Cys in this domain destabilize the fibril-like structures (Figure 4).

Furthermore, we interestingly found that for both types of incorporated binding sites – in the hydrophobic and hydrophilic regions, the identity of the metal-binding residue in a certain position leads towards a different preferable conformation of β-sheet fibrils that form the hydrogel. This suggests a possible control over the gel morphology.

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