Engineering of Silkworm Tyrosyl-tRNA Synthetase Variants to Create Halogenated Silk Fiber with Improved Thermal Stability.

Silk fiber, produced by the silkworm Bombyx mori, is a protein fiber with an excellent mechanical strength and broad biocompatibility. Multiple approaches, including genetic and chemical methods, must be combined to tailor silk fiber properties for wide applications, such as textiles and biomaterials. Genetic code expansion (GCE) is an alternative method to alter proteins' chemical and physical properties by incorporating synthetic amino acids into their primary structures. Here, we report an efficient system for selecting variants of B. mori tyrosyl-tRNA synthetase (BmTyrRS) used for GCE in silkworms. Four BmTyrRS variants with expanded substrate recognition toward halogenated tyrosine (Tyr) derivatives were selected, and transgenic silkworms expressing these variants were generated. The silkworms incorporated halogenated Tyr derivatives into silk fibroin to produce halogenated silk fiber with improved thermal stability. These results demonstrate the power of GCE to create protein materials with improved physical properties.