Abstract: The present application addresses the problem of providing an Fc-binding protein having an improved antibody separation ability. The present application also addresses the problem of providing a high-accuracy antibody separation method using an insoluble carrier having the protein immobilized thereon. The problems can be solved by: an Fc-binding protein in which at least an amino acid substitution at a specific position therein occurs and which has reduced affinity for an antibody; and an antibody separation method including allowing an equilibration buffer solution to pass through a column in which an insoluble carrier having the protein immobilized thereon is filled to equilibrate the column, adding a solution containing an antibody to cause the adsorption of the antibody onto the carrier, and eluting the antibody adsorbed on the carrier using an elution solution.

Abstract: The present application addresses the problem of providing an Fc-binding protein having an improved antibody separation ability. The present application also addresses the problem of providing a high-accuracy antibody separation method using an insoluble carrier having the protein immobilized thereon. The problems can be solved by: an Fc-binding protein in which at least an amino acid substitution at a specific position therein occurs and which has reduced affinity for an antibody; and an antibody separation method including allowing an equilibration buffer solution to pass through a column in which an insoluble carrier having the protein immobilized thereon is filled to equilibrate the column, adding a solution containing an antibody to cause the adsorption of the antibody onto the carrier, and eluting the antibody adsorbed on the carrier using an elution solution.