Proteins are the parts that make living engines run. They supply cells with energy, build muscle and bone, and catalyze countless other reactions that let the spark of life burn bright. To do their jobs, proteins must curl around substrate molecules, stretch to let their substrates go, travel around cells and assemble into work crews.
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Scientists have long believed that when an enzyme is empty, it gapes open like a hungry alligator, and that after it has caught its substrate, it remains closed until the reaction has been completed. Yang’s single-molecule microscopy studies have turned this notion upside-down. “Even when it has substrate, it doesn’t just bind the substrate tightly and stop moving. It’s still flapping,” he says. This constant motion makes perfect sense, considering how fast enzymes operate; some can process a million substrate molecules per minute. “Like a door, it has to be able to swing even without me going in and out.