Yeast Two Hybrid Screening of Photo-Switchable Protein-Protein Interaction Libraries.
Abstract: Although widely used in the detection and characterization of protein-protein interactions, Y2H screening has been under-used for the engineering of new optogenetic tools or the improvement of existing tools. Here we explore the feasibility of using Y2H selection and screening to evaluate libraries of photoswitchable protein-protein interactions. We targeted the interaction between circularly permuted photoactive yellow protein (cPYP) and its binding partner BoPD (binder of PYP dark state) by mutating a set of four surface residues of cPYP that contribute to the binding interface. A library of ~10,000 variants was expressed in yeast together with BoPD in a Y2H format. An initial selection for the cPYP/BoPD interaction was performed using a range of concentrations of the cPYP chromophore. As expected, the majority (>90% of cPYP variants no longer bound to BoPD). Replica plating was the used to evaluate the photoswitchability of the surviving clones. Photoswitchable cPYP variants with BoPD affinities equal to, or higher than, native cPYP were recovered in addition to variants with altered photocycles and binders that interacted with BoPD as apo-proteins. Y2H results reflected protein-protein interaction affinity, expression, photoswitchability and chromophore uptake, and correlated well with results obtained both in vitro and in mammalian cells. Thus, by systematic variation of selection parameters, Y2H screens can be effectively used to generate new optogenetic tools for controlling protein-protein interactions for use in diverse settings.