Generating Proteases with Custom Specificities

A team of researchers from Harvard University and the Broad Institute have rapidly evolved the botulinum toxin in the laboratory creating super-selective proteases with the potential to aid in neuroregeneration, regulate growth hormones, calm rampant inflammation, or dampen cytokine storm.

The team reported two accomplishments in a Science paper published last week. First, they successfully reprogrammed proteases to cut entirely new protein targets, even some with little or no similarity to the native targets of the starting proteases, and to simultaneously avoid engaging their original targets. Second, they also started to address what Travis Blum, first author on the study, called a "classical challenge in biology" designing treatments that can cross into a cell. Unlike most large proteins, botulinum toxin proteases can enter neurons in large numbers, giving them a wider reach that makes them all the more appealing as potential therapeutics.

The team's technology, called PACE (phage-assisted continuous evolution), can evolve custom proteases with tailor-made instructions for which protein to cut. "Such a capability could make 'editing the proteome' feasible," said David Liu, a co-author of the study, "in ways that complement the recent development of technologies to edit the genome."

Current gene-editing technologies often target chronic diseases like sickle cell anemia, caused by an underlying genetic error. Correct the error, and the symptoms fade. But some acute illnesses, like neurological damage following a stroke, aren't caused by a genetic mistake. That's where protease-based therapies come in: The proteins can help boost the body's ability to heal something like nerve damage through a temporary or even one-time treatment.

Scientists have been eager to use proteases to treat disease for decades. Unlike antibodies, which can only attack specific alien substances in the body, proteases can find and attach to any number of proteins, and, once bound, can do more than just destroy their target. They could, for example, reactivate dormant proteins. "Despite these important features, proteases have not been widely adopted as human therapeutics," said Liu, "primarily because of the lack of a technology to generate proteases that cleave protein targets of our choosing."