Modified fibroin fibers

A production method of a modified fibroin fiber, comprising a shrinking step of irreversibly shrinking a raw material fiber,

• wherein the raw material fiber contains modified fibroin, and before the shrinking step, the raw material fiber has a fiber diameter from 55 to 100 μm,
• wherein the modified fibroin comprises a domain sequence represented by Formula 1:
• [(A)n motif-REP]m or Formula 2:
• [A]n motif-REP]m-(A)n motif, in which:
• (A)n motif represents an amino acid sequence consisting of 2 to 27 amino acid residues, and a proportion of the number of alanine residues to a total number of amino acid residues in the (A)n motif is 40% or more;
• REP represents an amino acid sequence consisting of 2 to 200 amino acid residues;
• and
• m represents an integer from 2 to 300,
• wherein a plurality of (A)n motifs is the same amino acid sequences or different amino acid sequences, wherein a plurality of REP is the same amino acid sequences or different amino acid sequences, and wherein the domain sequence has an amino acid sequence corresponding to deletion of one or a plurality of glutamine residues in REP or substitution of one or a plurality of glutamine residues with another amino acid residue, as compared with the naturally derived fibroin.

A modified fibroin fiber comprising modified fibroin, wherein the modified fibroin fiber has a fiber diameter from 55 to 100 μm, and a shrinkage rate is 3.3% or less, the shrinkage rate being defined by the following Equation (1):

• Shrinkage rate (%)=(1−(length of modified fibroin fiber when dried from wet state/length of modified fibroin fiber when in wet state))×100,
• wherein the modified fibroin comprises a domain sequence represented by Formula 1:
• [(A) n motif-REP]m or Formula 2:
• [(A)n motif-REP]m-(A)n motif, in which:
• (A)n motif represents an amino acid sequence consisting of 2 to 27 amino acid residues, and a proportion of the number of alanine residues to a total number of amino acid residues in the (A)n motif is 40% or more;
• REP represents an amino acid sequence consisting of 2 to 200 amino acid residues;
• and
• m represents an integer from 2 to 300,
• wherein a plurality of (A)n motifs is the same amino acid sequences or different amino acid sequences, wherein a plurality of REP is the same amino acid sequences or different amino acid sequences, and wherein the domain sequence has an amino acid sequence corresponding to deletion of one or a plurality of glutamine residues in REP or substitution of one or a plurality of glutamine residues with another amino acid residue, as compared with the naturally derived fibroin.