Patent ID: 7771970

Claim:
A process of separating a protein of interest from a fusion protein, comprising the steps of: a) expressing a fusion protein comprising the protein of interest and a fusion partner in a bacterial host cell, wherein the fusion partner is a functional ubiquitin, and the charge of the fusion partner is changed by attaching an amino acid sequence consists of 2-30 amino acids consisting of at least one amino acid selected from the group consisting of histidine, lysine, arginine, glutamic acid, and aspartic acid to N-terminus of the fusion partner, and wherein the amino acid sequence has a different charge from that of the protein of interest to make a difference in the isoelectric point (pI) between the fusion partner and the protein of interest to be at least 1, wherein the protein of interest has pI of 7 or less, and the charge of the fusion partner is changed by attaching an amino acid sequence consists of 2-30 amino acids consisting of at least one amino acid selected from the group consisting of histidine, lysine, and arginine to N-terminus of the fusion partner, or the protein of interest has pI of more than 7, the charge of the fusion partner is changed by attaching an amino acid sequence consists of 2-30 amino acids consisting of at least one amino acid selected from the group consisting of glutamic acid, and aspartic acid to N-terminus of the fusion partner; b) loading the fusion protein on a matrix selected from the group consisting of an ion exchange resin and a membrane, wherein the matrix has a charge which is capable of adsorbing the fusion partner; c) treating the matrix adsorbing the fusion partner with ubiquitin cleavage enzyme to cleave the protein of interest; and d) eluting the cleaved protein of interest from the matrix.