SCHEME 1.

(Left) Sequence alignment of Selenoprotein F proteins from representative species. Signal peptide sequences are shown in gray color, and all Cys and Sec residues are highlighted. The UGGT-binding domain is boxed (UniProt ID: O60613, Q9ERR7 and Q9VVJ7 for Sep15 from human, mouse and fruit fly, respectively); (Right) NMR structure of the fruit fly Sep15, with only the C-terminal Trx-like domain (61–178) resolved and shown (PDB ID, 2A4H). The disulfide bond is shown in ball and stick representation.