Let the peptides shine: SOX (Sulfonamido-OXine)-labelled peptides for direct kinase and phosphatase monitoring

Abstract

Protein kinases and their cognate phosphatases are central regulators of cellular signalling, acting through the opposing processes of phosphorylation and dephosphorylation. Defects in kinase/phosphatase signalling are implicated in many diseases, including cancer, neurodegenerative conditions and metabolic disorders. Rapid and economical methods for measuring kinase activities are critically needed as diagnostic tools and for the evaluation of kinase inhibitors, including approaches that allow direct and quantitative measurement of kinase activities in complex media like cell lysates. SOX (sulfonamido-oxine)-labelled peptides, that upon phosphorylation chelate Mg²⁺ and undergo Chelation-Enhanced Fluorescence (CHEF), have emerged as a convenient class of modular kinase sensors. The development of an array of SOX-peptides has allowed researchers to gain insights into biological processes including binding events, conformational constraints, enzyme activities, protein trafficking and localization. This focused review provides an overview of the use of SOX-labelled peptides for probing kinase and phosphatase activity in real-time assays, including their development, synthesis, applications and strengths and weaknesses compared to other kinase assays.