C&EN: TODAY'S HEADLINES - CAN-DO CATALYSTS

AMANDA YARNELL

A team of european scientists has come up with what they think is an improved way to obtain highly efficient antibody catalysts. Using their all-in-vitro method, graduate student Sandro Cesaro-Tadic and biochemistry professor Andreas Plückthun of the University of Zurich; chemistry professor G. Michael Blackburn of the University of Sheffield, in England; and their coworkers have isolated a catalytic antibody capable of hydrolyzing phosphate monoesters [Nat. Biotechnol., published online May 18, http://dx.doi.org/10.1038/nbt828].

Their approach combines and improves upon several techniques that have already been reported: a fully synthetic antibody library with greater diversity than libraries obtained from mammalian immune systems, directed evolution to make further improvements to the best candidates from a library, and a selection method based directly on enzymatic turnover.

"Instead of extrapolating from established techniques what might one day be possible, we have actually done it," they tell C&EN.

The researchers begin with a library of 2 10⁹ synthetic antibodies, each displayed on the surface of a virus called a phage. They expose these phage-tethered antibodies to immobilized 2-difluoromethylphenyl phosphate. Those antibodies that can cleave the anchored substrate's phosphate ester bond produce a highly reactive intermediate that quickly traps the catalyst. Antibodies that succeed remain stuck to the surface, while those that fail are washed away. The catalytically most active antibody undergoes further rounds of random mutagenesis and selection to improve its activity.

The result is a phosphatase-like catalytic antibody with 1,000-fold higher catalytic efficiency than other catalytic antibodies for this inherently difficult reaction. Still, its catalytic efficiency remains only one-ten-thousandth that of alkaline phosphatase, the enzyme nature uses. The team hopes to further improve its antibody's catalytic prowess by improving the antibody's affinity for substrate.

In addition, Blackburn says the strategy can be easily adapted for other reactions and applied to even larger libraries.