fusion protein
A fusion protein is a single engineered protein assembled from useful parts of two or more different proteins, joined end to end. It is like building a new tool by welding the head of one instrument onto the handle of another, so the finished product gains the best feature of each component.
Because proteins are encoded by genes, scientists make a fusion protein by stitching the relevant pieces of DNA together and letting cells produce the combined molecule. A common design grabs the part of a natural receptor that catches a signaling molecule and fuses it to a piece of an antibody, the Fc region, which makes the drug last much longer in the blood and easier to manufacture.
Fusion proteins let designers mix and match functions: a binding domain to trap a target, an Fc tail for long half-life, or a toxin payload to kill a cell. As large biologics they are given by injection, and the artificial junction must be designed carefully so the protein folds correctly and does not provoke an unwanted immune response.
Etanercept is a fusion protein joining the TNF-binding part of a receptor to an antibody Fc tail, so it soaks up the inflammatory signal TNF and lasts long in the blood.
An engineered protein that combines a binding domain with a long-lasting antibody tail.
Fusing a therapeutic protein to an antibody Fc region is a standard way to extend its half-life from minutes to days.