Peptide codes for multiple protease activity assay via high-resolution mass spectrometric quantitation

The multifaceted role of proteases and modern analytical methods for investigation of their catalytic activity

We discuss the diverse functions of proteases in the context of their biotechnological and medical significance, as well as analytical approaches used to determine the functional activity of these enzymes. An insight into modern approaches to studying the kinetics and specificity of proteases, based on spectral (absorption, fluorescence), mass spectrometric, immunological, calorimetric, and electrochemical methods of analysis is given. We also examine in detail electrochemical systems for determining the activity and specificity of proteases. Particular attention is given to exploring innovative electrochemical systems based on the detection of the electrochemical oxidation signal of amino acid residues, thereby eliminating the need for extra redox labels in the process of peptide synthesis. In the review, we highlight the main prospects for the further development of electrochemical systems for the study of biotechnologically and medically significant proteases, which will enable the miniaturization of the analytical process for determining the catalytic activity of these enzymes.

The use of matrix-assisted laser desorption/ionization mass spectrometry in enzyme activity assays and its position in the context of other available methods

Activity assays are indispensable for studying biochemical properties of enzymes. The purposes of measuring activity are wide ranging from a simple detection of the presence of an enzyme to kinetic experiments evaluating the substrate specificity, reaction mechanisms, and susceptibility to inhibitors. Common activity assay methods include spectroscopy, electrochemical sensors, or liquid chromatography coupled with various detection techniques. This review focuses on the use of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) as a growing and modern alternative, which offers high speed of analysis, sensitivity, versatility, possibility of automation, and cost-effectiveness. It may reveal reaction intermediates, side products or measure more enzymes at once. The addition of an internal standard or calculating the ratios of the substrate and product peak intensities and areas overcome the inherent inhomogeneous distribution of analyte and matrix in the sample spot, which otherwise results in a poor reproducibility. Examples of the application of MALDI-TOF MS for assaying hydrolases (including peptidases and β-lactamases for antibiotic resistance tests) and other enzymes are provided. Concluding remarks summarize advantages and challenges coming from the present experience, and draw future perspectives such as a screening of large libraries of chemical compounds for their substrate or inhibitory properties towards enzymes.

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.

Mass Spectrometric Biosensing: A Powerful Approach for Multiplexed Analysis of Clinical Biomolecules

Rapid and sensitive detection of clinical biomolecules in a multiplexed fashion is of great importance for accurate diagnosis of diseases. Mass spectrometric (MS) approaches are exceptionally suitable for clinical analysis due to its high throughput, high sensitivity, and reliable qualitative and quantitative capabilities. To break through the bottleneck of MS technique for detecting high-molecular-weight substances with low ionization efficiency, the concept of mass spectrometric biosensing has been put forward by adopting mass spectrometric chips to recognize the targets and mass spectrometry to detect the signals switched by the recognition. In this review, the principle of mass spectrometric sensing, the construction of different mass tags used for biosensing, and the typical combination mode of mass spectrometric imaging (MSI) technique are summarized. Future perspectives including the design of portable matching platforms, exploitation of novel mass tags, development of effective signal amplification strategies, and standardization of MSI methodologies are proposed to promote the advancements and practical applications of mass spectrometric biosensing.

Novel Method for the Quantitative Analysis of Protease Activity: The Casein Plate Method and Its Applications

No simple methods are used for the quantitative analysis of the protease activity in colored food up till now. Thus, this study aims to establish a new and simple method for the quantitative detection of protease activity, especially in colored food. The detection accuracy, detection limit, and repeatability of the casein plate method were analyzed. Then, the application of the casein plate method in sample detection and recovery was further evaluated. The results showed that the casein plate method for the quantitative detection of protease activity has high accuracy, high precision, and low detection limit. The recoveries of eight kinds of colored samples were in the range of 92.26-97.84%, and the relative standard deviation (RSD) was in the range of 3.56-10.88%. The results of the casein plate method exhibited high accuracy. This indicated that the method was suitable for the detection of colored samples. The casein plate method for the quantitative detection of protease activity is simple. The newly constructed casein plate method has broad potential application value in food industry, especially for the detection of dark food.

A novel three-fluorophore system as a ratiometric sensor for multiple protease detection

A ratiometric fluorescent system for the detection of two proteases solely or in their mixture.