Inductively coupled plasma-mass spectrometry (ICP-MS) based assays lend themselves to multiplexing due to the high resolution between mass channels, the sensitivity, and the reliability of the technique. Here the potential of ICP-MS based protease assays is demonstrated with a quadruplex assay of cysteine proteases and metalloproteases. Four orthogonal peptide substrates were synthesized for the proteases calpain-1, caspase-3, MMP-9, and ADAM10. Each substrate carries a biotin tag at the C-terminus and a DTPA-based lanthanide complex at the N-terminus. The results demonstrate that this is simple and reproducible analysis technique with excellent correlation between the single and the multiplex assay formats. Keywords ICP-MS; Multiplex; Peptidase; Element-Tagging; LanthanidesProteases play crucial roles in all biological systems ranging from non-specific catabolism to specific signalling events. Disruption or acceleration of proteolysis of various protease substrates is observed in many diseases, making protease activity an important biomarker and a potential target for therapeutic intervention. 1, 2 Proteases rarely act alone but function in a 'protease web' and thus, the multiplex analysis of many proteases in a single assay would aid in the diagnosis of diseases through the identification of characteristic patterns of proteolytic activity. 3 Here we demonstrate a multiplex protease assay based upon lanthanide tagged protease substrates and ICP-MS analysis. There have been successful examples reporting multivariate bioassays for the detection of surface cell antigens 4 , glycoproteins 5 , and proteins 6, 7 using ICP-MS. The potential of ICP-MS based assays for multiplexed enzyme assays has not yet been realized.Recently, we demonstrated the use of a lanthanide-tagged protease substrate in a novel ICP-MS based protease assay. 8 Here we demonstrate that this ICP-MS assay can be readily adapted to a multiplexed protease assay. A quadruplex assay of two cysteine proteases, calpain-1 and caspase-3, and two metalloproteinases, MMP-9 and ADAM10, was carried out to demonstrate the potential of the multiplexed assay for the simultaneous detection of four different families of protease activity each with different requirements for activity.The design of the multiplex protease assay using ICP-MS is shown in Scheme 1. The assay is based on dual labeled peptide substrates that contain an N-terminal lanthanide chelate and a C-terminal biotin tag. All of the protease substrates were readily synthesized using standard Corresponding author: Mark Nitz, mnitz@chem.utoronto.ca, 416-946-0640. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and...
Rapid, sensitive and quantitative assays for proteases are important for drug development and in the diagnosis of disease. Here, an assay for protease activity which uses inductively coupled plasma-mass spectrometry (ICP-MS) detection is described. Peptidic α-chymotrypsin substrates were synthesized containing a lanthanide ion chelate at the N-terminus to provide a distinct elemental tag. A biotin label was appended to the C-terminus of the peptide allowing separation of uncleaved peptide from the enzymatic digestion. The enzyme activity was determined by quantifying the lanthanide ion signal of the peptide cleavage products by ICP-MS. Biotinylated substrates synthesized include Lu-DTPA-Asp-Leu-Leu-Val-Tyr∼Asp-Lys(Biotin) and Lu-DTPA-βAla-βAla-βAla-βAla-Gly-Ser-Ala-Tyr∼Gly-Lys-Arg-Lys(biotin)-amide. Parallel assays with a commercially available fluorogenic substrate (Suc-AAPF-AMC) for α-chymotrypsin were performed for comparison. Using the ICP-MS assay enzyme concentrations as low as 2 pM could be readily detected which was superior to the detection limit of an assay using the α-chymotrypsin fluorogenic substrate (Suc-AAPF-AMC). Furthermore, we demonstrated the use of this approach to detect chymotrypsin activity in HeLa cell lysates.
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