Controlled Sub-Nanometer Epitope Spacing in a Three-Dimensional Self-Assembled Peptide Hydrogel.

Cells in the body use a variety of mechanisms to ensure the specificity and efficacy of signal transduction. One way that this is achieved is through tight spatial control over the position of different proteins, signaling sequences, and biomolecules within and around cells. For instance, the extracellular matrix protein fibronectin presents RGDS and PHSRN sequences that synergistically bind the α5β1 integrin when separated by 3.2 nm but are unable to bind when this distance is >5.5 nm.1 Building biomaterials to controllably space different epitopes with subnanometer accuracy in a three-dimensional (3D) hydrogel is challenging. Here, we synthesized peptides that self-assemble into nanofiber hydrogels utilizing the β-sheet motif, which has a known regular spacing along the peptide backbone. By modifying specific locations along the peptide, we are able to controllably space different epitopes with subnanometer accuracy at distances from 0.7 nm to over 6 nm, which is within the size range of many protein clusters. Endothelial cells encapsulated within hydrogels displaying RGDS and PHSRN in the native 3.2 nm spacing showed a significant upregulation in the expression of the alpha 5 integrin subunit compared to those in hydrogels with a 6.2 nm spacing, demonstrating the physiological relevance of the spacing. Furthermore, after 24 h the cells in hydrogels with the 3.2 nm spacing appeared to be more spread with increased staining for the α5β1 integrin. This self-assembling peptide system can controllably space multiple epitopes with subnanometer accuracy, demonstrating an exciting platform to study the effects of ligand density and location on cells within a synthetic 3D environment.