Fusion protein

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A fusion protein is a protein created through genetic engineering from two or more proteins/peptides. This is achieved by creating a fusion gene: removing the stop codon from the DNA sequence of the first protein, then appending the DNA sequence of the second protein in frame. That DNA sequence will then be expressed by a cell as a single protein.

If the two entities are proteins, often linker (or "spacer") peptides are also added which make it more likely that the proteins fold independently and behave as expected. Especially in the case where the linkers enable protein purification, linkers in protein or peptide fusions are sometimes engineered with cleavage sites for proteases or chemical agents which enable the liberation of the two separate proteins.

Examples of biologic monoclonal antibody fusion proteins include the anti-TNF antibody etanercept and the anti OX40 monoclonal antibody OX40 Ig.

This technique is often used for identification and purification of proteins, by fusing a GST protein, FLAG peptide, or a hexa-his peptide (aka: a 6xhis-tag) which can be isolated using (affinity chromatography).