WOWing the crowds

A team of scientists at the Weizmann Institute of Science and the Hebrew University of Jerusalem has developed a method that could speed up the process of identifying novel protein molecules for medical or biological research hundreds of times over.

In today’s high-throughput searches for specific genes, proteins or protein interactions, plates containing rows of tiny wells have replaced old-fashioned test tubes. However, trawling for a gene or protein with just the right qualifications may require sorting through millions, or even billions, of possibilities. Instead of wells, the new method, developed by Dr. Dan Tawfik and Amir Aharoni of the Institute’s Biological Chemistry Department and Prof. Shlomo Magdassi of the Hebrew University’s Institute of Chemistry with support from the Israel Ministry of Science and Technology, relies on microscopic droplets of water suspended inside oil droplets. Using their system, millions of tests can be performed at once.

The method, which relies on a type of emulsion dubbed WOW, for water-oil-water, takes a page from living cells, which employ a fatty membrane to keep the inside and outside environments separate. The oily layer surrounding each miniscule water droplet acts as a barrier, keeping genes, proteins and other materials contained. Alternately, the team inserted harmless bacteria containing genes for testing into the drops. Confining individual tests within a cell-like bubble allowed them to employ a widely-used method for analyzing living cells. This method involves adding a fluorescent marker that lights up in color when activated by the right protein and sorting through the cells for those containing the marked proteins and their coding genes. Automated devices for sorting cells can handle many thousands of droplets per second. “Searches that now take a year to complete can be done in a matter of days,” says Tawfik.

To demonstrate the efficiency of the system, the team isolated a new enzyme from a gene that was mutated artificially to produce random variations. They generated the enzymes in the droplets and sorted them according to which ones were better at cleaving a specific toxin in the bloodstream. The results from a screen completed in one afternoon were equivalent to those previously obtained through several rounds of mutation and screening – a several-month process.