Fusion protein has two different meanings, one is the expression product of two genes recombined by DNA recombination technology. Another meaning is a group of proteins that mediate the fusion of two cell plasma membranes, such as one of the two glycoproteins contained in the outer leaflet of the Sendai virus lipid bilayer, which mediates the fusion of the viral envelope with the host cell plasma membrane. Another glycoprotein is hemagglutinin ceramidase.

Two different proteins are linked into one large molecule. It can be connected by chemical methods, or it can be achieved by gene fusion. In gene manipulation, some polypeptide genes with small molecular numbers are often connected to a gene (such as lac) by fusion, and a certain enzyme (such as thrombin) is connected between the two to increase the expression in the body. For the stability of the product, some deliberately fused two molecules in series to improve the efficacy, such as IL-3 and GM-CSF. There is also a fusion gene with the signal peptide gene of the secreted protein to secrete the expression product outside the membrane or outside the cell.

On the basis of the rapid development of genetic engineering, purposefully link two or more genes encoding functional proteins together to express the desired protein. This is achieved by combining the coding regions of two or more genes under artificial conditions. The protein product resulting from the expression of genes controlled by the same regulatory sequence is called a fusion protein.