New Chemical Tools to Modify and Study Proteins

One key approach used to modify proteins is to set up a reaction with the sulfur atom in the amino acid cysteine. However, the current methods used for this are still problematic in terms of efficiency, selectivity, and the stability of the final product. But in a study published today in Chem, researchers have developed a new method for modifying the amino acid cysteine on peptides and proteins.

The method uses a group of highly reactive organic molecules called ethynylbenziodoxolones (EBXs)—hyervalent iodine reagents that contain an iodine atom bound to three substituent groups. Using these reagents, the researchers generated a simple biomolecule–EBX adduct while keeping their reactive iodine group in the final molecule. The end products were protein–hypervalent iodine reagent chimeras that can act as dual attachment points for two new chemical groups, opening up new opportunities for the study of biological processes.

“One new functionality can be introduced via ‘click-chemistry,’ a well-established reaction in chemical biology,” says Jérôme Waser of EPFL. “Using a palladium catalyst, another selective modification can be achieved at the reactive iodine atom—what we would call a ‘biorthogonal’ functionality, as it does not exist in nature.” Introducing such exotic reactive groups into biomolecules is currently one of the most important tools in chemical biology, as it allows the study of biological processes without interfering with them.

The scientists demonstrated the potential of the method by introducing a diverse set of chemical groups into biomolecules. For example, the scientists used the dual handle to attach a fluorescent dye and a photoprotecting group into a neuropeptide simultaneously. Combining them improves the dye’s photostability and enables high-resolution, single-molecule imaging of molecular interactions.

Beyond peptides, the team further modified small proteins and even the large protein–DNA complexes called nucleosomes. As nucleosomes organize the genome, labeling them with fluorescent dyes can help track them to decipher how nature regulates gene expression.

“What we developed here is a new method for modifying proteins based on fundamental studies of chemical reactivity,” says Beat Fierz, also of EPFL. “We have already used it to modify histones, and carried out fluorescence experiments on living cells. With these examples, we have set the foundation for a better understanding of biological processes.”

Image: An illustration of the chemical reaction developed in the study. Image courtesy of J. Waser/B. Fierz (EPFL).