A Simple Assay for Proteases Based on Aggregation of Stimulus-Responsive Polypeptides

Unregulated changes in protease activity are linked to many diseases including cancer. Fast, accurate and low cost assays for detection of these changes are being explored for early diagnosis and monitoring of these diseases and can also be used as platforms for the discovery of new drugs. We report a new methodology for the simple detection and quantification of protease activity in buffer and human serum. The assay is based on recombinant diblock polypeptides that undergo temperature- or salt-triggered micellization in water. The coronae of the micelles are linked to the water insoluble cores by a peptide substrate that is cleaved in the presence of the target protease. Protease cleavage of the diblock polypeptide triggers the aggregation of the core-forming segment, leading to a change in solution optical density, which can be used to detect the presence of, and to quantify the concentration of, protease. We used matrix metalloproteinase-1 as a model protease and found peptide aggregation time to be proportional to enzyme concentration over a range from endogenous MMP-1 level in human serum (~3 ng/mL) to 100 ng/mL (0.15 nM to 5 nM) in 40% human serum and 1 ng/mL to 100 ng/mL in buffer. The assay does not require any intermediate steps or sophisticated data analysis and the modular design of the assay system is amenable to straightforward adaptation for the detection of a wide range of proteases.