This work reports on the use of protein engineering as a versatile tool to rationally design metal-binding proteins for the synthesis of highly photoluminescent protein-stabilized gold nanoclusters (Prot-AuNCs). The use of a single repeat protein scaffold allowed the incorporation of a set of designed metal-binding sites to understand the effect of the metal-coordinating residues and the protein environment on the photoluminescent (PL) properties of gold nanoclusters (AuNCs). The resulting Prot-AuNCs, synthesized by two sustainable procedures, showed size-tunable color emission and outstanding PL properties. In a second stage, tryptophan (Trp) residues were introduced at specific positions to provide an electron-rich protein environment and favor energy transfer from Trps to AuNCs. This modification resulted in improved PL properties relevant for future applications in sensing, biological labeling, catalysis, and optics.