Exploiting the concepts learnt from nature to build new nanomaterials from the bottom-up is critical for the efficient design of complex nanodevices. We demonstrate for the first time that the capacity of the ƒÑ-synuclein protein to assemble into nanofibers can be used for the controlled synthesis of metallic nanowires. Silver and platinum nanowires have been synthesized on a £\-synuclein protein fiber scaffold. The synthesized metallic nanowires have tunable diameters in the range 15 to 125 nm, achieved through the control of synthesis conditions. The platinum nanowires have lengths that were sufficiently large to enable electrical conductivity measurements that proved their electrical continuity. The integration of proteins into the bottom-up synthesis of metallic nanowires with controlled diameter makes the present approach of great interest for fabrication of nanodevices with applications in medicine and nanoelectronics.