The assembly of proteins into higher-order structures provides new routes to nanostructured materials. Amyloid proteins, which assemble into fibers having thickness of ~10 nm and lengths of 1 mm, represent a model system that is well-suited to exploring this new class of nanostructures. In an early example, a yeast amyloid protein was genetically engineered to introduce a single cysteine residue, which was then used to label the protein with a biotin ligand. This engineered protein was allowed to self-assemble into fibers, which were then captured onto a self-assembled monolayer presenting streptavidin proteins (which have very high binding affinity for biotin ligands).
The figure shows two adjacent fibers running vertically in parallel which were imaged in liquid with a new atomic force microscope (AFM) that is optimized for this function. The liquid imaging provides far more structural detail-including the periodically spaced "bumps" (~70nm spacing) on each fiber-than does imaging of dry fibers on mica. The periodic structure may be characteristic of the fiber assembly from smaller units or represent a helical twist of a structure with rectangular cross section.
This work illustrates a strategy for the complementary engineering of proteins and materials and which will provide further control of the architectures of the protein scaffold.
by Seth B. Darling, Milan Mrksich
Research in progress involving K. Y. Lee, S. Lindquist, M. Mrksich, and N. Scherer.