Researchers who want to screen proteins for specific enzyme activities could, in future, use a protein microarray system developed in Singapore.

Shao Yao and colleagues at the National University of Singapore have demonstrated this concept with cysteine proteases; enzymes which hydrolyse peptide bonds using a cysteine residue in their active site. These enzymes are inhibited by vinyl sulfone compounds, through a reaction with the cysteine residue in the protease. 

The group made a series of fluorescent probes which had a vinyl sulfone group on the end. They varied the structures by changing the amino acid recognition unit in each compound. A cocktail of these probes was used to screen enzymes which had been immobilised on a glass slide, some of which were cysteine proteases. These proteases could be identified because they were the only enzymes that the probes bound to, or labelled, giving a fluorescent signal.

Another microarray was used to screen the proteases with each of the probes, separately. Some of the proteases only act on substrates with specific amino acids in the peptide bond to be hydrolysed; these enzymes showed the strongest fluorescent signal with probes containing those amino acids. Others are more general and were labelled equally well by many of the probes. 'The resulting "protein fingerprints" reveal unique signatures for individual proteins, providing biological insights into the functional roles of the proteins' said Yao.

Yao explained that future challenges for the field would include the development of protein microarrays with detection methods that could give real-time data on enzyme activity. His group hope to extend their research to other kinds of enzymes, such as kinases and phosphatases. 

Rachel Warfield