An endogenous inhibitor of cysteine cathepsin B from brain tissues

Abstract

Lysosomes are the key degradative compartments of the cell in which the processes of protein degradation take place. Lysosomal cathepsins, which are enclosed in the lysosomes, help to maintain the homeostasis of the cell’s metabolism by participating in the degradation of heterophagic and autophagic material. When breaking down the integrity of lysosomal membranes the cathepsins are released into the cytosol and initiate the development of numerous pathological states. Breakdown in the control of protease activity leads to undesired and unregulated proteolysis. This is a cause of many diseases, such as Alzheimer’s disease, cancer, viral infections, cataracts etc. For this reason inhibitors of proteases have the potential to provide successful treatment for a wide range of diseases. Cathepsin B is one of the most abundant and ubiquitously expressed cysteine peptidases of the papain family. It is implicated in a number of pathological states including: inflammatory diseases of the airways, bone and joint disorders, acute pancreatitis, tumour metastasis, Alzheimer’s disease and ischemic neuronal death. The study of specific inhibitors for cathepsin B is considered important for chemotherapy and treatments of other diseases. This article represents part of a complex study of the lysosomal proteolytic-antiproteolytic system and its breakdown in the process of illness. In this article we present a scheme for extraction, purification and characterization of endogenous inhibitors of lysosomal cysteine cathepsin B. The cathepsin inhibitor was purified to homogeneity from the human neocortex. The purification was carried out in several successive stages: ammonium sulfate precipitation, followed by gel-filtration on Sephadex G-150, and ion exchange chromatography using DEAE-Sephadex A-75, followed by gel filtration on Sephadex G-100. Throughout the purification procedure, cathepsin inhibitory activity was controlled against the substrate p-nitroanilide N,α-benzoyl-D,L-arginine. Using graphic methods for analysis of enzymatic kinetics we proposed a mechanism of interaction of the endogenous inhibitor with cysteine cathepsin B. This scheme could prove useful for the understanding of biochemical mechanisms occurring in normal and, especially, in pathological human brain processes.