Fc-binding protein having improved acid stability, production method for said protein, and antibody-adsorbing agent using said protein

An Fc-binding protein, comprising:

• at least amino acid residues from glutamine at position 29 to glutamine at position 201 of the amino acid sequence set forth in SEQ ID NO:
• 2, with the proviso that the Fc-binding protein is modified with
• (i) amino acid modifications at the 6 positions indicated below:
• a substitution of isoleucine to valine at position 68 of SEQ ID NO:
• 2,
• a substitution of histidine to glutamine at position 80 of SEQ ID NO:
• 2,
• a substitution of serine to threonine at position 84 of SEQ ID NO:
• 2,
• a substitution of asparagine to threonine at position 90 of SEQ ID NO:
• 2,
• a substitution of asparagine to serine at position 91 of SEQ ID NO:
• 2, and
• a substitution of histidine to arginine at position 125 of SEQ ID NO:
• 2, and
• (ii) the amino acid modification indicated (1) below:
• (1) a substitution of leucine to serine at position 190 of SEQ ID NO:
• 2, and optionally, one or more of the modifications indicated in (2) to (12) below:
• (2) a substitution of isoleucine to threonine at position 45 of SEQ ID NO:
• 2,
• (3) a substitution of glutamine to leucine at position 69 of SEQ ID NO:
• 2,
• (4) a substitution of proline to leucine at position 83 of SEQ ID NO:
• 2,
• (5) a substitution of threonine to proline at position 123 of SEQ ID NO:
• 2,
• (6) a substitution of proline to glutamine at position 42 of SEQ ID NO:
• 2,
• (7) a substitution of proline to leucine at position 63 of SEQ ID NO:
• 2,
• (8) a substitution of asparagine to serine at position 75 of SEQ ID NO:
• 2,
• (9) a substitution of leucine to histidine at position 163 of SEQ ID NO:
• 2,
• (10) a substitution of aspartic acid to valine at position 179 of SEQ ID NO:
• 2,
• (11) a substitution of isoleucine to valine at position 198 of SEQ ID NO:
• 2, and
• (12) a deletion of serine at position 62 of SEQ ID NO:
• 2.