A miniaturized peptidyl-prolyl isomerase enzyme assay.

Prolyl-peptidyl isomerases (PPIases) are enzymes that are found in all living organisms. They form an essential part of the cellular protein folding homeostasis machinery. PPIases are associated with many important human diseases, e.g. cardiovascular disease, cancer and Alzheimer's. The development of novel PPIase inhibitors has been limited by the lack of a rapid, laboratory-based assay for these enzymes, as their substrates and products are challenging to distinguish. A well described continuous assay, coupled with the hydrolysis of a peptide by chymotrypsin is highly effective, but comparatively slow. To address this, we developed an improved version of the traditional assay using a temperature controlled plate reader. This assay allows semi-automated medium throughput assays in an academic laboratory for 84 samples per day. The assay shows lower errors, with an average Z' of 0.72. We further developed the assay using a fluorogenic peptide-based FRET probe. This provides an extremely sensitive PPIase assay using substrate at 200 nM, which approaches single turnover conditions. The fluorescent probe achieves an excellent quenching efficiency of 98.6%, and initial experiments showed acceptable Z' of 0.31 and 0.30 for cyclophilin A and hFKBP12 respectively. The assays provide an improved toolset for the quantitative, biochemical analysis of PPIases.