An Evolutionary Strategy for Identification of Higher Order, Green Fluorescent Host-Guest Pairs Compatible with Living Systems.

Engineered miniprotein host-small-molecule guest pairs could be utilized to design new processes within cells as well as investigate fundamental aspects of cell signaling mechanisms. However, the development of host-guest pairs capable of functioning in living systems has proven challenging. Moreover, few examples of host-guest pairs with stoichiometries other than 2:1 exist, significantly hindering the ability to study the influence of oligomerization state on signaling fidelity. Herein, we present an approach to identify host-guest systems for relatively small green fluorescent guests by incorporation into cyclic peptides. The optimal host-guest pair produced a 10-fold increase in green fluorescence signal upon binding. Biophysical characterization clearly demonstrated higher order supramolecular assembly, which could be visualized on the surface of living yeast cells using a turn-on fluorescence readout. This work further defines evolutionary design principles to afford host-guest pairs with stoichiometries other than 2:1 and enables the identification of spectrally orthogonal host-guest pairs.