Development of an enabling platform biotechnology for the production of proteins.

Protein-based drugs are a mainstay of modern medicine. In contrast to antibodies, most of these need highly individualized production processes which often limits their development. Here, we develop an immunoglobulin domain tag (i-Tag), which can be fused to any protein of interest. This tag is made of a linear arrangement of antibody light chain constant domains. It enhances expression as well as secretion of the fusion partner and allows for simple purification of several structurally and functionally distinct fusion proteins. Furthermore, it improves the biophysical characteristics of most fusion proteins tested, is inert, and does not compromise the fusion partners' functionality. Taken together, the i-Tag should facilitate the development of biopharmaceuticals and diagnostic proteins otherwise lacking a common structural element.