The "foldon domain" is a structural element found in certain proteins, notably in the design of proteins for various biotechnological applications. It is a small, stable protein domain that is engineered to facilitate the folding of larger proteins into their correct three-dimensional shapes. Foldon domains are often incorporated into recombinant proteins as a way to enhance their stability and improve their folding efficiency. These domains can promote proper protein folding by encouraging the formation of specific interactions and structures within the protein chain. In biotechnology, foldon domains are frequently used in the design of protein scaffolds, fusion proteins, and other engineered proteins for applications ranging from drug delivery to biomaterials.