UC Berkeley

Natural filamentous shaped biomolecules utilize their physical shape and chemical functionality to optimize and achieve hierarchical structures. They use weak interaction such as hydrogen bonds, hydrophobic interaction, charge-charge interaction, van der Waals force and so on. The major advantage of using weak interactions is that they enable biomolecules to adopt the reversible assembly and reorganization of the structures. In my work, I use M13 bacteriophage (M13 phage) to investigate how intrinsic molecular interaction affect phase transition, self-assembly process, and hierarchical structure formation. I used genetically engineered phage with the peptide motif of elastin-like polypeptide (ELP). Insertion of target sequence of peptide on the surface of M13 phage can endow functionality on the M13 phage. Firstly, I investigated novel liquid crystalline transition upon stimuli application. Counterintuitive liquid crystalline order increase upon heating was investigated with engineered M13 phage. Secondly, molecular crowding environment make M13 phage forming long-range ordered smectic structures. The addition of non-interacting colloidal particles provides depletion force to phage and accelerate their assembly. Due to the intrinsic molecular interaction engineered phage, I investigated time dependent structure evolution process. Last, I applied ELP as interacting colloids to engineered phage. Because ELP possesses same peptide motif, they could have interaction despite different molecular shape. Unlike the mixture system of phage and non-interacting colloids, engineered phage and ELP mixture system showed dual phase transition and helical fiber formation. Furthermore, I could turn off and on the depletion force by controlling temperature. I show that our novel liquid crystalline phase transition is based on the attractive interaction. Through my dissertation, I hope the combination of functionality of peptide and liquid crystal molecule could convey the insight for molecular design and development of hierarchical structure formation.