In CALI, chromophores (red) produce reactive species to inactivate a target protein
US scientists can now compare molecular warheads that inactivate proteins.
Chromophore assisted light inactivation (CALI) of proteins involves generating highly reactive species (often singlet oxygen) from a chromophore (the warhead) using light. The reactive species damages the target protein, inactivating its biological function. Thomas Kodadek, a chemical biologist at University of Texas Southwestern Medical Centre, explained that CALI can be used to 'knock-out the function of a protein to validate pharmaceutical targets or alternatively provide temporal control of protein inactivation for mechanistic studies.'
Organic chromophores often react with the reactive species they produce, limiting their effectiveness as CALI warheads. In this new research, Kodadek and his co-workers have developed a system for comparing warhead effectiveness. The system allows different chromophores to be covalently attached to a standard target protein through a simple coupling mechanism. This allows the chromophore efficiencies to be compared by measuring the remaining activity of the target.
Comparative experiments showed a ruthenium-based chromophore to be a more effective warhead than the commonly used organic dye fluorescein. The scientists demonstrated that the ruthenium chromophore can enter cells and inactivate a target, opening up the possibility of CALI experiments on living cells as well as cell extracts.