UC San Diego

From only 20 amino acid building blocks, nature has designed and refined protein structures for a wide variety of specific purposes. Each protein molecule carries out a specific function in nature (structural component, transportation, catalysis, among myriad others) that is directly related to the structure of protein. Despite this impressive diversity, many proteins do not operate alone, but combine with other molecules—lipids, carbohydrates, nucleic acids, co-factors, and other proteins—to fulfill their functional roles. Consequently, understanding the structural properties of proteins and their interactions with other types of macromolecules provides insights for creating advanced protein-based hybrid components with tunable properties. Synthetic polymers are a large class of macromolecules that stand out in terms of their chemical diversity, tunable composition, controlled length (and thus physical properties) and easy acquisition. Thus, synthetic polymers have been commonly employed to augment the functional properties of proteins as well as creating hybrid materials with different proteins. Here, we have utilized synthetic polymers in a new context, namely in combination of protein crystals, to create a novel form of materials that seamlessly combine the advantages of proteins (functional diversity and atomically precise tailorability), crystalline materials (structural order and coherence) with those of synthetic polymers (flexibility, dynamics and stimuli-responsiveness). In this dissertation, we first report the combination of rigid/ordered ferritin crystals with superabsorbent polymers to create dynamic, self-healing, stimuli-responsive polymer-integrated-crystals (PIX). The so-formed hybrid materials possess the flexibility of the polymer components and the structural order of the protein crystals, and the macroscopic dynamicity arising from these two components can be controlled by changing the pH and ionic strength (Chapter 2). Following the initial success of the first PIX, we sought to expand the scope of utility for PIX materials by investigating the behavior of PIX by systematically varying polymer composition, ferritin surface charge, crystal packing, and identity of the crystallized protein. We carried out experiments and simulations to understand the individual effect of different components on the system. With a better understanding of the PIX system, we demonstrated that the properties of the PIX can be tuned by controlling pH and ionic strength, as mentioned above (Chapter 3). Finally, we showed that the original PIX system can be used as a platform for controlled encapsulation/release of target biomolecules in a size-selective fashion (Chapter 4). Overall, we have created a novel class of materials with unique physical and mechanical properties that possess tremendous potential for use in applications such as molecular storage/delivery and compartmentalized chemical reactions.