AbstractThe construction of a template‐assembled synthetic protein (TASP) designed to contain both a 4‐helix bundle and a β‐barrel as two folding “domains” is described. For thede novodesign of proteins, amphiphilic helices (α) and β‐sheets (β) are covalently attached to a template peptide (T) carrying functional side chains suitably oriented to promote intarmolecular folding of the secondary structure blocks into a characteristic packing arrangement, i.e., T8‐(4α)(4β). The design of this new macromolecule was assisted by computer modeling, which suggested a low‐energy conformation with tight hydrophobic packing of the secondary structure subunits. Solid‐phase synthesis of the “two‐domain” TASP molecule was achieved using orthogonal protection techniques. The solution properties as well as circular dichroism (CD) and infrared spectroscopy (IR) data under various experimental conditions are consistent with the folded confo