Method for preparing polymeric protein composed of monomeric protein produced by fusing protein having immunoglobulin fold structure to protein capable of serving as subunit structure

A method for producing a multimeric protein consisting of two or more monomeric protein, wherein said monomeric protein is obtained by fusing a protein having an immunoglobulin fold structure to either a protein or a functional fragment thereof that can serve as a subunit structure, the method comprising the steps of:

• (A) preparing a monomeric protein having an insoluble granular form in cells of a microorganism, the monomeric protein obtained by fusing a first protein having an immunoglobulin fold structure to a second different protein that can serve as a subunit structure;
• (B) solubilizing the monomeric protein prepared in step (A) with an aqueous solution comprising lauroyl glutamic acid and/or a salt thereof, resulting in a first solution;
• (C) adding a phosphate buffer to the first solution obtained in step (B) so that the concentration of the lauroyl glutamic acid and/or salt thereof is 2 to 5%;
• (D) diluting the solution obtained in step (C) in a buffer comprising arginine and/or an arginine derivative to lower the concentration of lauroyl glutamic acid and/or a salt thereof, resulting in a second solution;
• and
• (E) replacing a solvent of the second solution obtained in step (C) with a buffer, resulting in removal said lauroyl glutamic acid and/or a salt thereof, using a method selected from the group consisting of:
• (e1) column chromatography selected from the group consisting of gel filtration chromatography, ion-exchange chromatography, hydrophobic interaction chromatography, and combination thereof;
• (e2) ultrafiltration;
• (e3) dialysis;
• and
• (e4) combinations thereof.