Dynamic Materials Based on a Protein Conformational Change

Abstract

Natural proteins perform a variety of functions in biological systems, including actuation, catalysis, structural support, and molecular sequestering. The variety of natural protein functions suggest that they could serve as valuable and versatile building blocks for synthesis of functional materials. Based on this premise, several investigators have developed schemes to include functional proteins into hydrogel networks to take advantage of their structural, catalytic, and ligand binding properties. Natural proteins such as collagen [1] and elastin [2] have been used to develop materials with tailored structural and mechanical properties, while catalysis by enzymes (e.g., glucose oxidase [3] ) has been used to build smart, environmentally-responsive hydrogel networks. The ability of proteins to selectively bind ligands has been used to develop materials that change their degree of physical or chemical crosslinking in the presence of biological antigens, [4,5] small molecule drugs, [6] and carbohydrates, [7][8][9] resulting in environmentallyresponsive biomaterials. In each of these previous studies a nanometer-scale function associated with a specific protein was exploited to build a material that performed an intriguing macroscopic function. A function that has not been explored as extensively in materials science is the ability of proteins to undergo complex conformational changes. Proteins change conformations in response to a broad range of stimuli, including light, pH, and the binding of biological molecules. Over 200 conformational changes are well-characterized, [10] representing a vast unexplored databank of molecular building blocks for design of dynamic materials. Recent studies have demonstrated the utility of protein conformational changes in nano-scale engineered systems, including cooperative nanometer-scale motors [11] and molecular shuttles, [12] suggesting that dynamic protein molecules could also be a useful component of 3-dimensional materials. To that end, we recently reported an approach that used a dynamic protein as a partial cross-linker in a chemically cross-linked hydrogel network, and these hydrogels changed their volume in the presence of a specific protein-binding molecule.[13] Here we describe assembly of protein-based, dynamic materials using a novel photochemical approach. This approach allows for high concentrations of protein to be functionally included into a network in response to light, and the resulting materials undergo striking volume changes upon protein-ligand binding. Photochemical assembly also enables spatial control over the location of dynamic proteins in a hydrogel network, which is likely to be important in potential materials science and engineering applications.

Moving from static to dynamic complexity in hydrogel design

“…5). In some cases, these hydrogels can respond to a biological input by releasing an output, as demonstrated by insulin release in response to glucose catalysis 82 or biochemically triggered growth factor release 83,84 .…”

An adaptable hydrogel array format for 3-dimensional cell culture and analysis

“…In these experiments a 10X excess of acrylate-terminated PEG chains (Mw=8kDa) or (PEG-DTT)n-PEG conjugates were incubated with a CGGRGDSP peptide at 37°C for 90 minutes in PBS to allow for Michael-type addition of the cysteine sulfhydryl group to the acrylate group, as described previously [39][40][41]. The resulting solutions contained PEG-diacrylate and acrylate-PEG-CGGRGDSP molecules that were subsequently photo-crosslinked to form cell-interactive hydrogel networks.…”

Triggered Drug Release from Dynamic Microspheres via a Protein Conformational Change

“…Specifically, our approach relies on a ligand-induced protein conformational change to induce changes in hydrogel properties. In our general approach, which has been detailed previously, [5][6][7] In this study we formed and characterized dynamic hydrogel microspheres in which a protein conformational change was used to control microsphere volume changes and the release of an encapsulated drug. In particular, a specific biochemical ligand, trifluoperazine, induced calmodulin's nanometer scale conformation change, which translated to a 48.7% microsphere volume decrease.…”

“…PEG-CaM-PEG conjugates were synthesized, purified, and characterized as previously described. [5][6][7] PEG 575 -CaM-PEG 575 microspheres were formed using a water-in-oil emulsion polymerization in an Argon environment. The same process was repeated with a different water phase containing PEGDA 575 to form PEG 575 microspheres.…”

“…Volume changes were calculated assuming isotropic volume changes. [6] To quantify VEGF release from microspheres, PEG 575 -CaM-PEG 575 microspheres were incubated in a solution containing recombinant human VEGF (Invitrogen, Carlsbad, CA) (0.13 mg Á ml…”