A protein includes an amino acid sequence derived from a sequence selected from the group consisting of SEQ ID NOs: 1 to 5. The amino acid sequence includes a substitution of a hydrophobic amino acid residue in an Fc binding site with a different hydrophobic amino acid residue or a polar uncharged amino acid residue, and the protein has a reduced antibody-binding capacity in an acidic pH range, as compared to a protein including the amino acid sequence without the substitution.