Novel Photoproteins for Imaging

Green fluorescent protein and its relatives have revolutionized imaging in the biological sciences at the microscopic level. Their genetically encoded and autocatalytic nature underlies their versatility as cellular markers, protein localization tags, and components of biochemical sensors. On the other hand, the GFP-type autocatalytic fluorescent proteins (AFPs) have not been used widely for whole-body imaging in mammals, and had not been considered as scaffolds for engineering optical control of protein activity. We will report new findings extending AFPs into these applications as well. We have engineered bright far-red AFPs that provide sub- stantially better signal over background in deep-tissue imaging compared to phytochrome-based proteins, enabling longitudinal visualization of stem cell differentiation in mice. We also discovered a previously unknown feature of variants of the photochromic green AFP Dronpa, the ability to undergo light-dependent dissociation and association. We used this feature to create light-controllable proteins of a simple modular design that is generalizable and has self-reporting abilities, features that have yet to be achieved by other photoactive protein domains. AFPs thus can serve as the basis for rational design of light-controllable proteins, a long-standing aim in protein engineering research. Our findings extend the applications of FPs to new imaging modalities as well as beyond imaging to optogenetic control.

Speaker: Michael Lin, Stanford