Enzyme-coupled assays for proteases

The sulfonimidamide as a novel transition state analog for aspartic acid and metallo proteases

We have developed a novel strategy for the preparation of tetrahedral transition state analogs for aspartic acid and metallo-proteases based upon the sulfonimidamide functional group. Our best alpha-des-amino dipeptide analog binds at least 100-fold tighter than the corresponding ground state structure (i.e., amide). A previously unpublished five-membered cyclic sulfonimidamide was also synthesized.

General protease assay method coupling solid-phase substrate extraction and capillary electrophoresis

Capillary electrophoresis with laser-induced fluorescence detection was used to develop a universal, highly specific protease assay. In this method, a peptide, biotinylated at the N-terminus, is labeled with fluorescein at a lysine residue near the C-terminus. Impurities are removed from the fluorescence labeling mixture by solid-phase extraction of the substrate on immobilized streptavidin, followed by extensive washing. The purified fluorescent substrate is dissociated from the streptavidin and incubated with the protease. The peptide sequence between the biotin and fluorescent label contains the cleavage sequence of the protease of interest. After cleavage, the fluorescent product does not contain a biotin group. A second solid-phase extraction is used to remove unreacted substrate to dramatically lower the background signal. The product is detected by capillary electrophoresis, which provides powerful discrimination against products generated by nonspecific proteases. With chymotrypsin as a test protease, product was detected with as little as 10 pg/mL (4.6 x 10(-13) M) chymotrypsin, or 5 amol of enzyme in the 10-microL sample volume.