Sensitive array-based assay for determination of serological protein kinase A autoantibody levels based on its antigen protein activation

Preventive Effects of Thermosensitive Biopolymer-Conjugated C-Peptide against High Glucose-Induced Endothelial Cell Dysfunction

C-peptide has emerged as a potential drug for treating diabetic complications. However, clinical application of C-peptide is limited by its short half-life during circulation and costly synthesis methods. To overcome these limitations, a biocompatible and thermosensitive biopolymer-C-peptide conjugate composed of human C-peptide genetically conjugated at the C-terminus of nine repeats of lysine-containing elastin-like polypeptide (K9-C-peptide) is generated. K9-C-peptide exhibits reversible thermal phase behavior with a transition temperature dependent on polypeptide concentration. Degradation of K9-C-peptide hydrogel depends on the concentration of four cleavage enzymes as well as the reaction time and frequency of treatments with elastase-2. The preventive effect of K9-C-peptide against high glucose-induced human aortic endothelial cell dysfunction is further investigated. K9-C-peptide inhibits high glucose-induced intracellular reactive oxygen species generation, transglutaminase 2 activation, and apoptosis, similar to the inhibitory effects of human C-peptide. Thus, K9-C-peptide is a potential drug depot for the sustained delivery of C-peptide to treat diabetic complications.

High-throughput investigation of transglutaminase 2 kinase regulation using a novel cysteine-modified peptide array

Transglutaminase 2 (TGase2) kinase has emerged as an important regulator of apoptosis as well as chromatin structure and function; however, details about the pathophysiological functions of TGase2 kinase have been limited because of the lack of a suitable activity assay for systematic investigation of TGase2 kinase regulation in a high-throughput manner. Thus, we developed a novel on-chip TGase2 kinase activity assay using a cysteine-modified insulin-like growth factor-binding protein-3-derived peptide (CMI peptide) on an array platform. This peptide array-based activity assay was reproducible, with a detection limit of 2.127 μg/ml. We successfully applied this assay to investigate the effects of thiol-reactive compounds and divalent cations on TGase2 kinase by determining the half maximal inhibitory concentrations (IC₅₀). Thiol-reactive compounds inhibited TGase2 kinase activity in a concentration-dependent manner, with IC₅₀ values ranging from 0.125 to 5.550 mM. Divalent metal cations also showed a concentration-dependent inhibition, with IC₅₀ values ranging from 0.005 to 1.937 mM; however, Ca²⁺ had no effect on TGase2 kinase activity. Thus, this novel kinase activity assay using the CMI peptide array described here is suitable for systematic investigation of TGase2 kinase regulation and may be useful for investigating the roles of TGase2 kinase in pathogenesis of kinase-mediated diseases.

Systematic investigation of protein kinase A substrate proteins using on-chip protein kinase kinetic profiling

An on-chip protein kinase assay for profiling kinase kinetic parameters by introducing the substrate affinity (K_m) and the phosphorylation rate (V_p) under physiological conditions.

Array-Based High-Throughput Analysis of Silk-Elastinlike Protein Polymer Degradation and C-Peptide Release by Proteases

The objective of this study was to utilize an on-chip degradation assay to evaluate polymer depots and the predicted drug release from the depots. We conjugated four silk-elastinlike protein (SELP) polymers including SELP-815K, SELP-815K-RS1, SELP-815K-RS2, and SELP-815K-RS5 with a Cy5-NHS ester and fabricated SELP arrays by immobilizing the conjugated polymers onto well-type amine arrays. SELP polymer degradation rates were investigated by calculating the half-maximal effective concentration (EC50). Eight cleavage enzymes were applied, all of which exhibited distinctive EC50 values for SELP-815K and its three analogues. We successfully utilized this assay to study the in vitro release of the Cy5-conjugated C-peptide from SELP-815K hydrogel arrays. Additionally, cumulative C-peptide release from the SELP-815K depots was also demonstrated using repetitive elastase treatments. Therefore, this array-based on-chip degradation assay could potentially be used for evaluating depot degradation and controlled drug release from polymer depots at the molecular level.

Identification of transglutaminase 2 kinase substrates using a novel on-chip activity assay

Transglutaminase 2 (TG2) is an enzyme that plays a critical role in a wide variety of cellular processes through its multifunctional activities. TG2 kinase has emerged as an important regulator of apoptosis, as well as of chromatin structure and function. However, systematic investigation of TG2 kinase substrates is limited due to a lack of a suitable TG2 kinase activity assays. Thus, we developed a novel on-chip TG2 kinase activity assay for quantitative determination of TG2 kinase activity and for screening TG2 kinase substrate proteins in a high-throughput manner. Quantitative TG2 kinase activity was determined by selective detection of substrate protein phosphorylation on the surface of well-type amine arrays. The limit of detection (LOD) of this assay was 4.34μg/ml. We successfully applied this new activity assay to the kinetic analysis of 27 TG2-related proteins for TG2 kinase activity in a high-throughput manner and determined Michaelis-Menten constants (Km) of these proteins. We used the Km values and cellular locations of the TG2-related proteins to construct a substrate affinity map for TG2 kinase. Therefore, this on-chip TG2 kinase activity assay has a strong potential for the systematic investigation of substrate proteins and will be helpful for studying new physiological functions.

Real-time monitoring of glucose-6-phosphate dehydrogenase activity using liquid droplet arrays and its application to human plasma samples

Glucose-6-phosphate dehydrogenase (G6PD) regulates nicotinamide adenine dinucleotide phosphate (NADPH) levels and is related to the pathogenesis of various diseases, including G6PD deficiency, type 2 diabetes, aldosterone-induced endothelial dysfunction, and cancer. Therefore, a highly sensitive array-based assay for determining quantitative G6PD activity is required. Here, we developed an on-chip G6PD activity assay using liquid droplet fluorescence arrays. Quantitative G6PD activity was determined by calculating reduced resorufin concentrations in liquid droplets. The limit of detection (LOD) of this assay was 0.162 mU/ml (2.89 pM), which is much more sensitive than previous assays. We used our activity assay to determine kinetic parameters, including Michaelis-Menten constants (Km) and maximum rates of enzymatic reaction (Vmax) for NADP(+) and G6P, and half-maximal inhibitory concentrations (IC50). We successfully applied this new assay to determine G6PD activity in human plasma from normal healthy individuals (n=30) and patients with inflammation (n=30). The inflammatory group showed much higher G6PD activities than did the normal group (p<0.001), with a high area under the curve value of 0.939. Therefore, this new activity assay has the potential to be used for diagnosis of G6PD-associated diseases and utilizing kinetic studies.