poly his tag where a series of approximately six histidine amino acid residues are added which enables the protein to bind to protein purification matrices chelated to metal ions such as nickel or cobalt other tags commonly used in protein purification include strep tag chitin binding protein maltose binding protein glutathione s transferase and flag tag tags such as u201c epitope tags u201d may also confer the protein to have an affinity towards an antibody common antibody epitope tags include the v5 tag myc tag and ha tag the terms u201c fusion protein u201d or u201c fused protein u201d refer to a protein that is coded by a single gene and the single gene is made up of coding sequences that originally coded for at least two or more separate proteins a fusion protein may retain the functional domains of the two or more separate proteins part of the coding sequence for a fusion protein may code for an epitope tag as described herein for the antibody like protein a fusion protein may also contain sequences that code for a variety of proteins having vary functional roles based on its application u201c polypeptides u201d u201c chromatography u201d is the collective term for a set of laboratory techniques for the separation of mixtures the mixture is dissolved in a fluid called the mobile phase which.