Figure 1. AFM single-molecule force spectroscopy on protein receptor-ligand complexes. (Left) Schematic of the experimental setup where Coh and Doc form a non-covalent molecular complex. (Middle) Upon separating the cantilever tip and surface, marker domains 1 and 2 (MD1, MD2) unfold in series providing identifiable contour length increments (ΔLc). The last peak in the trace represents rupture of the receptor-ligand complex. (Right) Depending on the anchor point of the proteins to the cantilever tip/surface, we can apply force to the complex under different loading geometries, and steer the complex down specific unfolding energy landscapes.
• Single-molecule force spectroscopy (SMFS) with the atomic force microscope (AFM) quantifies the resistance of individual molecules and molecular complexes to applied forces. We use this technique to study protein folding/unfolding transitions, and to characterize dynamic fluctuations of molecules with the aim of understanding how proteins perform their intended functions at the molecular level. Through these experiments we seek to understand what makes protein interactions mechanically strong, or weak, and to incorporate these aspects into engineering of biological materials. This information is also beneficial for understanding systems where mechanical forces play a significant biological role (e.g., cell adhesion to surfaces, cell interactions with extracellular matrix).
Figure 2. Enzyme-mediated and antibody-mediated polymerization systems are being developed as a signal-amplification strategy for immunological biosensing (top), as well as in cell/gel encapsulation for cell isolation and screening (bottom & right).
• Several naturally occurring enzymes can be utilized for polymerization/cross-linking of synthetic compounds. At the same time, polymerization initiators can be coupled with affinity proteins for cell encapsulation. We are pursuing enzyme-mediated and affinity protein-mediated polymerization as a method for interfacing synthetic polymers/hydrogels with cells in a controlled way. Our goal is to develop synthetic biological systems that are capable of initiating polymerization, directing assembly and orienting cells with respect to one another and with respect to surfaces. We envision application of these systems in cell screening, disease diagnosis, tissue engineering, and as a foundational tool for building up synthetic tissues. See our poster from Biointerfaces Zurich, 2016 by clicking here.
Smart polymers and proteins
Figure 3. Stimuli-responsive or ‘smart’ polymers and proteins exhibit hydrated coil conformations below a critical threshold. Upon raising the temperature above this threshold, the polymer undergoes an entropically-driven conformational change. Over time collision of the collapsed chains leads to macroscale aggregation and precipitation.
• Smart polymers undergo dramatic conformational changes in response to slight changes in environmental conditions. Examples include small changes in pH, temperature, salt, and light that give rise to collapse or expansion of polymer chains in aqueous media. These environmentally responsive materials act as nanoscale signal transducers, or molecular amplifiers that sense their surroundings and respond with an output signal. We work with both synthetic polymers and elastin-like polypeptides (i.e., repetitive protein polymers) possessing ‘smart’ properties. Here we are interested in integrating smart materials into synthetic molecular systems to control biomolecular activity in a predictable way, for example, by modulating surface adhesion and friction, by controlling biological activity (e.g., enzymatic activity), or by directing nanoparticle self-assembly.