Fluorogenic Peptide Substrate for Quantification of Bacterial Enzyme Activities

Physico-chemical characterization studies of collagen labelled with Ru(II) polypyridyl complex

The rich luminescence behaviour exerted by transition metal complexes has found significant role in the development of biomolecular and cellular probes. The conjugation of fluorophore to a protein has its own advantage over the label-free system due to its high sensitivity. While numerous proteins have been labelled with either organic or inorganic fluorophores, the conjugation of luminescent transition metal complexes with collagen has not yet been attempted. Here, in this study, the conjugation of a Ru(II) polypyridyl complex with collagen was carried out and its physico-chemical characterization was studied. The conjugation of Ru(II) to collagen was characterized by UV-Visible, fluorescence and ATR-FT-IR spectroscopy. The conjugation of Ru(II) did not alter the triple helical structure of the collagen as evidenced from CD spectral data. The luminescence behaviour of the Ru-tagged collagen was found to be similar to that of the commercially available fluorescein isothiocyanate (FITC) tagged collagen with increase in luminescence upon addition of collagenase. Gel-based collagenase assay showed that the digestion of collagen can be vizualized using UV light due to intrinsic fluorophore tag without carrying out the staining-destaining processes. Energy dispersive X-Ray analysis (EDAX) confirms the presence of Ru in Ru-collagen fibrils. To the best of our knowledge, this is the first report on the conjugation of a Ru(II) complex with the fibrous protein collagen that exhibits similar property as of FITC-collagen and can be used as an alternative.

The role of polymeric chains as a protective environment for improving the stability and efficiency of fluorogenic peptide substrates

We have faced the preparation of fully water-soluble fluorescent peptide substrate with long-term environmental stability (in solution more than 35 weeks) and, accordingly, with stable results in the use of this probe in determining the activity of enzymes. We have achieved this goal by preparing a co-polymer of the commercial N-vinyl-2-pyrrolidone (99.5% mol) and a fluorescent substrate for trypsin activity determination having a vinylic group (0.5%). The activity of trypsin has been measured in water solutions of this polymer over time, contrasted against the activity of both the commercial substrate Z-L-Arg-7-amido-4-methylcoumarin hydrochloride and its monomeric derivative, prepared ad-hoc. Initially, the activity of the sensory polymer was 74.53 ± 1.72 nmol/min/mg of enzyme, while that of the commercial substrate was 20.44 ± 0.65 nmol/min/mg of enzyme, the former maintained stable along weeks and the latter with a deep decay to zero in three weeks. The ‘protection’ effect exerted by the polymer chain has been studied by solvation studies by UV–Vis spectroscopy, steady-state & time resolved fluorescence, thermogravimetry and isothermal titration calorimetry.

CDK5 positively regulates Notch1 signaling in pancreatic cancer cells by phosphorylation

The marked overexpression of cyclin‐dependent kinase 5 (CDK5) or Notch1 receptor, which plays critical roles in pancreatic ductal adenocarcinoma (PDAC) development, has been detected in numerous PDAC cell lines and tissues. Although, a previous study has demonstrated that CDK5 inhibition disrupts Notch1 functions in human umbilical vein endothelial cells, the mechanism underlying Notch1 activation regulated by CDK5 remains unclear. Herein, we identified a physical interaction between CDK5 and Notch1 in PDAC cells, with the Notch1 peptide phosphorylated by CDK5/p25 kinase. CDK5 blockade resulted in the profound inhibition of Notch signaling. Accordingly, CDK5 inhibition sensitized PDAC cell proliferation and migration following Notch inhibition. In conclusion, CDK5 positively regulates Notch1 function via phosphorylation, which in turn promotes cell proliferation and migration. The combinational inhibition of CDK5 and Notch signaling may be an effective strategy in the treatment of PDAC.

An Internally Quenched Fluorescent Peptide Substrate for Protealysin

Protealysin, a metalloprotease of Serratia proteamaculans, is the prototype of a subgroup of the M4 peptidase family. Protealysin-like proteases (PLPs) are widely spread in bacteria but also occur in fungi and certain archaea. The interest in PLPs is primarily due to their putative involvement in the bacterial pathogenesis in animals and plants. Studying PLPs requires an efficient quantitative assay for their activity; however, no such assay has been reported so far. Here, we used the autoprocessing site sequence of the protealysin precursor to construct an internally quenched fluorescent peptide substrate 2-aminobenzoyl-L-arginyl-L-seryl-L-valyl-L-isoleucyl-L-(ε-2,4-dinitrophenyl)lysine. Protealysin and thermolysin, the prototype of the M4 family, proved to hydrolyze only the Ser-Val bond of the substrate. The substrate exhibited a K_M = 35 ± 4 μM and k_cat = 21 ± 1 s⁻¹ for protealysin as well as a K_M = 33 ± 8 μM and k_cat = 7 ± 1 s⁻¹ for thermolysin at 37 °C. Comparison of the effect of different enzymes (thermolysin, trypsin, chymotrypsin, savinase, and pronase E) on the substrate has demonstrated that it is not strictly specific for protealysin; however, this enzyme has higher molar activity even compared to the closely related thermolysin. Thus, the proposed substrate can be advantageous for quantitative studies of protealysin as well as for activity assays of other M4 peptidases.

Evaluation of collagenase gold plus BP protease in isolating islets from human pancreata

Selection of enzymes for optimal pancreas digestion is essential for successful human islet isolations. The aim of this study was to evaluate the efficacy and outcome of using Collagenase Gold plus BP protease (VitaCyte) (n = 8) by comparing it to two commercially available enzymes, Liberase MTF C/T (Roche) (n = 48) and Collagenase NB1/NP (Serva) (n = 15). The isolation outcomes were assessed by islet counting, viability, glucose-stimulated oxygen consumption rate (OCR), and successful graft-rate following transplantation in diabetic NOD scid mice. The pancreas donor characteristics were not significantly different between the tested enzyme groups regarding their BMI, pancreas weight, cold ischemia time (CIT) and HbA1c. The results show that digested tissue volume was not statistically significant between the VitaCyte enzyme (34.25 ± 5.4 mL) and the Roche enzyme (55.25 ± 3.42 mL, p = 0.073), however, this was significant with Serva enzyme (64.07 ± 7.95 mL, p = 0.020). Interestingly, the islet yields were not statistically different between all enzyme groups. Moreover, when islets were transplanted into NOD scid mice, the reversal rate of diabetes for the VitaCyte enzyme group was similar to all enzyme groups. In conclusion, the effectiveness of Collagenase Gold plus BP protease is comparable to the MTF C/T and the Collagenase NB1/NP enzymes; the low cost could facilitate the use of more pancreata for islet isolations.

Beneficial effect of recombinant rC1rC2 collagenases on human islet function: Efficacy of low-dose enzymes on pancreas digestion and yield

A high number of human islets can be isolated by using modern purified tissue dissociation enzymes; however, this requires the use of >20 Wunsch units (WU)/g of pancreas for digestion. Attempts to reduce this dose have resulted in pancreas underdigestion and poor islet recovery but improved islet function. In this study, we achieved a high number of functional islets using a low dose of recombinant collagenase enzyme mixture (RCEM-1200 WU rC2 and 10 million collagen-degrading activity [CDA] U of rC1 containing about 209 mg of collagenase to digest a 100-g pancreas). The collagenase dose used in these isolations is about 42% of the natural collagenase enzyme mixture (NCEM) dose commonly used to digest a 100-g pancreas. Low-dose RCEM was efficient in digesting entire pancreases to obtain higher yield (5535 ± 830 and 2582 ± 925 islet equivalent/g, P < .05) and less undigested tissue (16.7 ± 5% and 37.8 ± 3%, P < .05) compared with low-dose NCEM (12WU/g). Additionally, low-dose RCEM islets retained better morphology (confirmed with scanning electron microscopy) and higher in vitro basal insulin release (2391 ± 1342 and 1778 ± 978 μU/mL; P < .05) compared with standard-dose NCEM. Nude mouse bioassay demonstrated better islet function for low-dose RCEM (area under the curve [AUC] 24 968) compared with low-dose (AUC-38 225) or standard-dose NCEM (AUC-38 685), P < .05. This is the first report indicating that islet function can be improved by using low-dose rC1rC2 (RCEM).