The incorporation of Janus particles into the repertoire of nanoscale building blocks adds a new level of control to supramolecular assembly. Here we demonstrate the potential for using toposelective modification to assemble new types of targeting nanoplatforms by docking the universal coupling protein, streptavidin (StAv), onto a restricted region of the surface of a small protein cage. The resulting StAv-functionalized Janus particles have the potential to be used to control the orientation of the nanoplatforms targeted to a cell surface. In addition, the StAv-biotin couple provides an ideal molecular adaptor for extending asymmetric (polarized) supramolecular assembly. To demonstrate this potential application, StAv-functionalized nanoplatforms were coupled to a biotinylated monoclonal antibody and used to target a microbial pathogen.