Mass-Encoded Suspension Array for Multiplex Detection of Matrix Metalloproteinase Activities.

This work designed a mass spectrometric biosensing strategy for the multiplex detection of matrix metalloproteinases (MMPs) with a mass-encoded suspension array. This array was fabricated as multiplex sensing probes by functionalizing magnetic beads with MMP-specific peptide-isobaric tags for relative and absolute quantification (iTRAQ) conjugates, which contained a hexahistidine tag for surface binding, a substrate region for MMP cleavage, and a coding region for the specific MMP. The integration of the multiplex coding ability of iTRAQ with ultrahigh performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) and the proteolysis method for peptide digestion endowed the biosensing method with high throughput and ultrahigh sensitivity. This strategy could be conveniently performed by mixing the sample and the suspension array for enzymatic reactions and then digesting the uncleaved peptides with trypsin to release the coding regions for UPLC-MS/MS analysis. With MMP-2 and MMP-7 as analytes, the relative changes of peak area ratios of coding regions showed good linear responses in the ranges of 0.2-100 and 0.5-400 ng mL-1, with detection limits of 0.064 and 0.17 ng mL-1, respectively. The analysis of MMP activity in serum samples and its change responding to inhibitors demonstrated the specificity, practicability, and expansibility of the proposed strategy. This work paves a new avenue for the activity assays of multiplex enzymes and promotes the development of mass spectrometric biosensing.