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Self-Assembled Protein Polymers for the Development of Nanostructured Biomaterials

Wesley D. Marner II, University of California, Berkeley, 201 Gilman Hall, Berkeley, CA 94720, Susan J. Muller, Chemical Engineering, University of California at Berkeley, Berkeley, CA 94720, and Jay D. Keasling, Department of Chemical Engineering, University of California, Berkeley, 201 Gilman Hall, Berkeley, CA 94720.

Genetic engineering and protein expression techniques offer unprecedented control over the primary sequence of recombinantly-produced proteins. Materials science techniques provide extensive knowledge about the design and characterization of synthetic polymers. We propose to combine these areas of expertise to facilitate de novo design of novel, fully artificial proteins. We have investigated a class of self-assembling amphiphilic protein polymers that self-assemble into well-ordered, nanostructured hydrogels. In particular, we studied poly(EAK)n, a protein polymer with n repeats of the amino acid monomer sequence AEAEAKAKAEAEAKAK. This class of protein forms robust hydrogels in saline solutions.

After our explorations of self-assembling homopolymers, we are now investigating translational fusion proteins that combine the poly(EAK)n domain with another structural or functional element. Preliminary experiments indicate that the mechanical and morphological properties of these gels can be tuned by varying characteristics of the amino acid sequence or by changing the identity of the fusion domain. We have also demonstrated the ability to modulate nanoscale feature dimensions and morphology of the hydrogel matrix. In this paper, we describe the challenges of producing these unique biomolecules. We also discuss the physical properties of these structural proteins and the usefulness of fusion proteins incorporating both structural and chemically functional moieties.