Directing Complex Biomacromolecular Assembly Using Triggers

Tufts University, Medford MA

Investigators

Abstract

The objective of the proposed study is to understand how to 'control' or 'direct' the process of morphology development in polymeric materials using external influences or molecular 'triggers'. As we move towards more specialized polymeric systems with more demanding properties specifications more refined and powerful methods to control morphology will be required. Fibrous proteins provide a convenient 'bridge' between biological organization and synthetic polymer design and are therefore useful models to fill this need. To achieve the objective, protein-based triggers will be designed into silk consensus repeats. Based on preliminary data, the molecular triggers (chemical oxidation/reduction of methionines and enzymatic phosphorylation/dephosphorylation) function as intended - the phosphorylation trigger strongly alters conformation but a high degree of crystallinity is attained, whereas the methionine trigger preferentially blocks crystallization but b-strand conformation persists to moderate oxidation levels. Therefore, triggers that are conformation- versus crystallization-selective and separately initiate different length scales in self-assembly are available to be incorporated into the polymer designs to control complex pathways of assembly. Using these features the PI expects to be able to direct polymer assembly depending on placement of the different triggers in relation to the sequence motifs, as well as using external triggering of these blocks on a temporal basis. These features may allow generation of distinct material morphologies from the same polymer sequence, as well as formation of gradient structures. A series of synthetic peptides with systematic variations in the location and nature of molecular triggers will be used to assess impact on assembly, including insigts into triggering kinetics, distribution of secondary structures (in solution and in the solid state), crystallization kinetics, crystal structure and solubility. Subsequently, longer sequence combinations will be constructed by genetic engineering and assessed in a similar fashion. A variety of analytical tools, including MALDI, FTIR, CD, X-ray, TEM/diffraction analysis will be used to assess structure formation at different length scales. In the final stages of the project, these concepts will be utilized to assemble materials with gradient morphologies. %%% This project is in a growing area at the interface of polymeric materials science and biotechnology. The ability to control the pathway of polymer assembly in more precise ways, from the molecular level to macromolecular architecture, will provide important processing avenues in the fabrication of new materials with tailored structure/morphologies.