Within project C11 of the SFB 677 researchers at the Otto-Diels- Institute of Organic Chemistry at the Christian-Albrechts-University, Kiel, aim to modify a naturally occurring antifreeze protein from the fish winter flounder to be able to switch its activity off and on by light. The video describes the background of this proteins, its mechanism of action, and the steps needed to modify it and make its activity light sensitive.