Strategic Utilization of the Photophysical and Photochemical Properties of Luminescent Transition Metal Complexes as Synthetic Substrates for Protein Tags

Description

In this project, we aim to develop new photofunctional transition metal complexes asnovel synthetic substrates for protein tags including the SNAP-tag, CLIP-tag, andHaloTag. The analysis and evaluation of protein functions have been greatly assisted bythe development of protein tag technology. In this strategy, the protein of interest istagged with a low-molecular weight protein or polypeptide, which is subsequentlymodified with a synthetic label such as an organic fluorophore or other targetingmolecules. Currently, the three most widely used protein tags are the SNAP-tag, CLIP-tag,and HaloTag. Although a number of fluorescent substrates for these tags have beendeveloped, their use requires stringent washing after labeling because unlabeled probesremaining inside the cells can lead to strong background fluorescence. Thus, one of thecurrent challenges is the development of fluorogenic probes that show fluorescenceturn-on after bioconjugation. The protein tag technology has also facilitated thedevelopment of chromophore-assisted light inactivation (CALI). This technique employsa chromophore as a photosensitizer that produces reactive oxygen species (ROS) such assinglet oxygen upon irradiation; the latter can damage proteins in close vicinity of thechromophore. Although various protein tag substrates have been utilized, there is a lackof candidates that show high singlet oxygen production quantum yields and at the sametime remain photostable upon irradiation. To date, nearly all of the fluorescent probesand photosensitizers developed as SNAP-tag, CLIP-tag, and HaloTag substrates areorganic dyes. Although the interesting luminescence properties of transition metalcomplexes have been widely utilized in biosensing and bioimaging as demonstrated by usand other research groups, the idea of using metal complexes as substrates for proteintags has not been explored. In this project, we will design new substrates for the SNAP-tag, CLIP-tag, and HaloTag based on photofunctional transition metal complexes. Thephotophysical and photochemical properties of the complexes and their reactivity towardthe protein tags will be investigated. Additionally, the cellular uptake, cytotoxicity, andbioimaging properties of the complexes, and their applications in CALI of proteins andintracellular biosensing will be examined. We believe that a combination of thespecificity associated with the genetically encoded protein tags and the intriguingphotophysical and photochemical properties of transition metal complexes will afforduseful bioimaging, protein-inactivating, and biosensing reagents. Ultimately, we arevery confident that the results generated from this project will lead to the developmentof biological and medical reagents with useful diagnostic and therapeutic applications.