We demonstrate the fabrication of protein center dot gold nanoparticle (AuNP) nanocomposites in situ, leading to distinct assemblies dependent upon protein secondary structure. In the presence of pentameric coiled-coil proteins C and Q, which contain histidine tags and have helicities of 54 and 65%, respectively, templation of AuNP results in precipitation of the protein center dot AuNP composites with AuNPs 6.5 nm in diameter, creating macromolecular assemblies on the micrometer scale. In the absence of the histidine tags, the resulting Cx and Qx proteins, which exhibit lower helicities of 37 and 45%, respectively, stabilize soluble protein center dot AuNP composites with AuNPs 4.5 nm in diameter for several days without aggregating. By manipulating protein structure via external triggers, such as TFE, we obtain control over the macromolecular conformation and overall physicochemical properties. These hybrid protein center dot AuNP assemblies can be readily deposited on electrodes, where they can serve as a tunable bionanocomposite kinetic barrier.