Abstract: The present invention relates to a modified fibroin including a domain sequence represented by Formula 1: [(A)n motif-REP]m or Formula 2: [(A)n motif-REP]m-(A)n motif, and having a serine residue content rate of less than 5.5%. [In Formula 1 and Formula 2, the (A)n motif represents an amino acid sequence consisting of 4 to 27 amino acid residues, and the number of alanine residues with respect to the total number of amino acid residues in the (A)n motif is 80% or more. REP represents an amino acid sequence consisting of 10 to 200 amino acid residues. m represents an integer of 10 to 300. The plurality of (A)n motifs may be the same amino acid sequence or different amino acid sequences. A plurality of REPs may be the same amino acid sequence or different amino acid sequences.

Abstract: The present invention provides a modified fibroin fiber having a shrinkage history of being irreversibly shrunk after spinning, the modified fibroin fiber containing modified fibroin, wherein a fiber diameter of a raw material fiber before being irreversibly shrunk exceeds 25 ?m.

Abstract: Provided is a side-by-side type composite fiber having a latent crimping ability, including a first component containing a modified fibroin and a second component containing a structural protein, in which the first component and the second component are joined to each other.