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Six new putative cysteine protease inhibitors based upon sequences of the N-terminal binding fragments of rat cystatin A, bovine cystatin C and human cystatins D and S were synthesized. Inhibitory activities of these compounds against papain and bovine cathepsin B were tested. Additionally, agar well diffusion test of their antibacterial activity against Streptococcus pyogenes was performed.
Content available remote Fluorogenic peptide substrates for carboxydipeptidase activity of cathepsin B.
Cathepsin B is a lysosomal cysteine protease exhibiting mainly dipeptidyl carboxypeptidase activity, which decreases dramatically above pH 5.5, when the enzyme starts acting as an endopeptidase. Since the common cathepsin B assays are performed at pH 6 and do not distinguish between these activities, we synthesized a series of peptide substrates specifically designed for the carboxydipeptidase activity of cathepsin B. The amino-acid sequences of the P5-P1 part of these substrates were based on the binding fragments of cystatin C and cystatin SA, the natural reversible inhibitors of papain-like cysteine protease. The sequences of the P'1-P'2 dipeptide fragments of the substrates were chosen on the basis of the specificity of the S'1-S'2 sites of the cathepsin B catalytic cleft. The rates of hydrolysis by cathepsin B and papain, the archetypal cysteine protease, were monitored by a continuous fluorescence assay based on internal resonance energy transfer from an Edans to a Dabcyl group. The fluorescence energy donor and acceptor were attached to the C- and the N-terminal amino-acid residues, respectively. The kinetics of hydrolysis followed the Michaelis-Menten model. Out of all the examined peptides Dabcyl-R-L-V-G-F- E(Edans) turned out to be a very good substrate for both papain and cathepsin B at both pH 6 and pH 5. The replacement of Glu by Asp turned this peptide into an exclusive substrate for cathepsin B not hydrolyzed by papain. The substitution of Phe by Nal in the original substrate caused an increase of the specificity constant for cathepsin B at pH 5, and a significant decrease at pH 6. The results of kinetic studies also suggest that Arg in position P4 is not important for the exopeptidase activity of cathepsin B, and that introducing Glu in place of Val in position P2 causes an increase of the substrate preference towards this activity.
Content available remote Structural studies of cysteine proteases and their inhibitors.
Cysteine proteases (CPs) are responsible for many biochemical processes occurring in living organisms and they have been implicated in the development and progression of several diseases that involve abnormal protein turnover. The activity of CPs is regulated among others by their specific inhibitors: cystatins. The main aim of this review is to discuss the structure-activity relationships of cysteine proteases and cystatins, as well as of some synthetic inhibitors of cysteine proteases structurally based on the binding fragments of cystatins.
Large intestine malignancy is the second most common malignancy and second leading cause of cancer mortality in Poland. This is related to late detection of these lesions, e.g. due to lack of effective screening tests. Lesions found by a surgeon are clinically advanced, making the treatment often ineffective and sometimes even completely impossible. Discovery of a substance that would be able to stop key processes for the development of malignancy could change such situation. Activity of certain enzymes was found to increase in malignant cells and invasion of malignancy could be triggered by inadequate amount of endogenous inhibitors of these enzymes in the surrounding healthy tissues. Inhibitors identical with that produced in human cells were found in egg whites.The aim of the study was to determine ability of cystatin isolated from egg whites to inhibit activity of cathepsin B and L.Material and methods. Immunohistochemistry and histology of tissue specimen collected from malignant lesions resected from 60 patients diagnosed with large intestine adenocarcinoma, who underwent surgical treatment in 2nd Department of General and Oncological Surgery, Medical University of Wrocław between 2007 and 2009.Results. Differences were fund between health tissues, margins and center of the malignant lesions with regard to amount and distribution of stained cathepsin B - cystatin complexes. The above mentioned inhibitors were able to inhibit 90% of primary activity of cathepsin B and L in malignant tissues.Conclusions. Cystatins obtained from egg whites could be used as substances supporting anti-cancer therapy in the future.
Content available remote Modes of inhibition of cysteine proteases.
Cysteine proteases are involved in many physiological processes and their hyperactivity may lead to severe diseases. Nature has developed various strategies to protect cells and whole organisms against undesired proteolysis. One of them is the control of proteolytic activity by inhibition. This paper presents the mechanisms underlying the action of proteinaceous inhibitors of cysteine proteinases and covers propeptides binding backwards relative to the substrate or distorting the protease catalytic centre similarly to serpins, the p35 protein binding covalently to the enzyme, and cystatins that are exosite binding inhibitors. The paper also discusses tyropins and chagasins that, although unrelated to cystatins, inhibit cysteine proteinases by a similar mechanism, as well as inhibitors of the apoptosis protein family that bind in a direction opposite to that of the substrate, similarly to profragments. Special attention is given to staphostatins, a novel family of inhibitors acting in an unusual manner.
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