In vivo regulation of an endogenously-tagged protein by a light-regulated kinase

Post-translational modifications (PTMs) are indispensable modulators of protein activity. Most cellular behaviours, from cell division to cytoskeletal organization, are controlled by PTMs, their miss-regulation being associated with a plethora of human diseases. Traditionally, the role of PTMs has been studied employing biochemical techniques. However, these approaches fall short when studying PTM dynamics in vivo . In recent years, functionalized protein binders have allowed the post-translational modification of endogenous proteins by bringing an enzymatic domain in close proximity to the protein they recognize. To date, most of these methods lack the temporal control necessary to understand the complex effects triggered by PTMs. In this study, we have developed a method to phosphorylate endogenous Myosin in a light-inducible manner. The method relies both on nanobody-targeting and light-inducible activation in order to achieve both tight specificity and temporal control. We demonstrate that this technology is able to disrupt cytoskeletal dynamics during Drosophila embryonic development. Together, our results highlight the potential of combining optogenetics and protein binders for the study of the proteome in multicellular systems.