The F54L mutation of Thioredoxin shows protein instability and increased fluctuations of the catalytic center

Baba, Takumi*; Ueno, Go*; Oe, Chika*; Saji, Shuku*; Yamamoto, Sachiko*; Yamamoto, Masaki*; Nakagawa, Hiroshi   ; Okazaki, Nobuo*; Ouchida, Mamoru*; Kawasaki-Ohmori, Iori*; Takeshita, Kohei*

Neuronal degeneration and chronic kidney disease have been observed in Trx-F54L mutant rats; however, the details of why the Trx mutation causes these phenomena remain unknown. This study investigates molecular changes caused by the F54L mutation and explores the factors contributing to the Adem rat phenotype. Results showed that the F54L mutant was less active than WT Txn1 on insulin substrates, but no significant difference in redox potential was observed. On the other hand, F54L is more sensitive to degeneration in the body temperature range than the wild type. Furthermore, the crystal structure showed that F54 formed hydrophobic interactions with the surrounding hydrophobic amino acids. Moreover, the MD simulation results show increased fluctuations around the F54L mutation, as well as a tendency for the distance between residues C32 and C35 at the catalytic center to widen. The molecular dynamics of the F54L mutation may affect the substrate reduction activity, thermal stability, and kinetic stability.