Abstract: The purpose of the present invention is to provide a novel protein, which have such excellent pH responsiveness that the antibody binding property to the Fc region of the immunoglobulin in the neutral region is improved and the binding property to the Fc region of the immunoglobulin in the weakly acidic region is much decreased when compared to the wild-type proteins such as protein G and protein A that have affinity for the protein comprising the Fc region of the immunoglobulin G (IgG), and a mutant-type protein (an improved protein) comprising their domain mutant. The present invention relates to a protein constituted by linking plural domains having affinity for a protein comprising the Fc region of the immunoglobulin G (IgG) with linkers, wherein an extended length to the maximum of the linker is 80-240 angstrom.

Abstract: The purpose of the present invention is to provide a superior protein with more decreased binding property to the Fc region of immunoglobulin and/or more decreased binding property to the Fab region thereof in the weakly acidic region in comparison with a protein containing an extracellular domain of a wild-type protein G without spoiling the high antibody binding property in the neutral region, and to allow the antibody to be easily captured and recovered without denaturing it by means of a capturing agent and column comprising the above protein.

Abstract: The purpose of the present invention is: to provide an excellent protein which is further reduced in the binding property to an Fc region of an immunoglobulin and/or the binding property to an Fab region of the immunoglobulin in a weakly acidic region compared with that of a protein containing an extracellular domain of wild-type protein G, and which still keeps a high antibody-binding activity in a neutral region; and to capture and collect an antibody readily using the protein without denaturating the antibody.