Rational design and self-assembly of coiled-coil linked SasG protein fibrils.

Protein engineering is an attractive approach for the self-assembly of nanometre-scale architectures for a range of potential nanotechnologies. Using the versatile chemistry provided by protein folding and assembly, coupled with amino acid side-chain functionality, allows for the construction of precise molecular "protein origami" hierarchical patterned structures for a range of nano-applications such as stand-alone enzymatic pathways and molecular machines. The Staphyloccocus aureus surface protein SasG is a rigid, rod-like structure shown to have high mechanical strength due to 'clamp-like' intra-domain features and a stabilising interface between G5 and E domains, making it an excellent building block for molecular self-assembly. Here we characterise a new two sub-unit system composed of the SasG rod protein genetically conjugated with \emph{de novo} designed coiled-coils, resulting in the self-assembly of fibrils. Circular dichroism (CD) and quartz-crystal microbalance with dissipation (QCM-D) are used to show the specific, alternating, binding between the two subunits. Furthermore, we use atomic force microscopy (AFM) to study the extent of subunit polymerisation in a liquid environment, demonstrating self-assembly culminating in formation of linear macromolecular fibrils.