Reagent Nabs Enzyme Protein Substrates

A reagent and a method used to identify the protein substrates of enzymes that install acetyl groups on proteins will make it easier for scientists to study how the acetyl chemical tags help orchestrate complex biological processes (J. Am. Chem. Soc. 2006, 128, 15356). Mounting evidence suggests that acetyltransferase enzymes, including those that modify the histone proteins that package human genetic material, add acetyl groups to far more protein substrates than once imagined, notes John S. Blanchard of Albert Einstein College of Medicine, Bronx, N.Y. His team's method can be used to reveal all substrates of a given acetyltransferase. The researchers start with a chlorinated version of the enzymes' normal acetyl group source, acetyl-coenzyme A. When this reagent and the acetyltransferase are added to cell extracts, the enzyme transfers a chloroacetyl group (green) to each of its protein substrates (red) to give the protein product shown. The chloroacetyl group serves as a reactive handle for substrate identification; addition of a cysteamine-derivatized rhodamine dye (blue) yields fluorescently labeled protein upon chloride elimination.