Significance Designed protein assemblies have many applications in medicine and technology. A long-standing design paradigm generates assemblies through genetic fusion of homo-oligomers via α-helical linkers. Here, we introduce a rigid fusion strategy that finds a greater number of design solutions and reduces formation of unintended assembly states, and a method for doubly anchoring target binding domains in the resulting assemblies that could contribute to cryogenic electron microscopy structure determination of small proteins.