Biomaterial Database

Degradation of ricin A chain by endosomal and lysosomal enzymes--the protective role of ricin B chain. 1994

A Bilge, and J Howell-Clark, and S Ramakrishnan, and O W Press

Department of Biological Structure, University of Washington, Seattle 98195, USA.

We investigated the role of intracellular processing of ricin A chain (RTA) by proteolytic enzymes on the expression of its ribosome inhibitory activity. Endosomal and lysosomal proteases extracted from Jurkat cells and purified cathepsins B, D and G were incubated with RTA, resulting in generation of a 28-kDa fragment by proteolytic cleavage. This process was reminiscent of the nicking of Pseudomonas exotoxin and Diphtheria toxin by intracellular proteases to produce functionally active toxin fragments. However, the ribosome inhibitory activity of the purified 28-kDa fragment of RTA was 11,000-fold less than that of native RTA, suggesting that such cleavage is not an essential step in the cytotoxic activity of the toxin. Addition of ricin B chain (RTB) in degradation assays resulted in the protection of RTA from proteolytic activities of lysosomes and cathepsins. However, RTB did not protect another RNA acting protein, RNAase; nor did excess amounts of unlabeled RTA or IgG protect labelled RTA from degradation, suggesting that the protective effect of RTB was specific to its interaction with RTA. Such a protective role for RTB may partially account for the higher toxicity of immunotoxins (ITs) containing whole ricin compared to ITs containing only RTA.

UI	MeSH Term	Description	Entries
D008247	Lysosomes	A class of morphologically heterogeneous cytoplasmic particles in animal and plant tissues characterized by their content of hydrolytic enzymes and the structure-linked latency of these enzymes. The intracellular functions of lysosomes depend on their lytic potential. The single unit membrane of the lysosome acts as a barrier between the enzymes enclosed in the lysosome and the external substrate. The activity of the enzymes contained in lysosomes is limited or nil unless the vesicle in which they are enclosed is ruptured or undergoes MEMBRANE FUSION. (From Rieger et al., Glossary of Genetics: Classical and Molecular, 5th ed).	Autolysosome,Autolysosomes,Lysosome
D010449	Peptide Mapping	Analysis of PEPTIDES that are generated from the digestion or fragmentation of a protein or mixture of PROTEINS, by ELECTROPHORESIS; CHROMATOGRAPHY; or MASS SPECTROMETRY. The resulting peptide fingerprints are analyzed for a variety of purposes including the identification of the proteins in a sample, GENETIC POLYMORPHISMS, patterns of gene expression, and patterns diagnostic for diseases.	Fingerprints, Peptide,Peptide Fingerprinting,Protein Fingerprinting,Fingerprints, Protein,Fingerprint, Peptide,Fingerprint, Protein,Fingerprinting, Peptide,Fingerprinting, Protein,Mapping, Peptide,Peptide Fingerprint,Peptide Fingerprints,Protein Fingerprint,Protein Fingerprints
D011500	Protein Synthesis Inhibitors	Compounds which inhibit the synthesis of proteins. They are usually ANTI-BACTERIAL AGENTS or toxins. Mechanism of the action of inhibition includes the interruption of peptide-chain elongation, the blocking the A site of ribosomes, the misreading of the genetic code or the prevention of the attachment of oligosaccharide side chains to glycoproteins.	Protein Synthesis Antagonist,Protein Synthesis Antagonists,Protein Synthesis Inhibitor,Antagonist, Protein Synthesis,Antagonists, Protein Synthesis,Inhibitor, Protein Synthesis,Inhibitors, Protein Synthesis,Synthesis Antagonist, Protein,Synthesis Inhibitor, Protein
D011992	Endosomes	Cytoplasmic vesicles formed when COATED VESICLES shed their CLATHRIN coat. Endosomes internalize macromolecules bound by receptors on the cell surface.	Receptosomes,Endosome,Receptosome
D002403	Cathepsins	A group of lysosomal proteinases or endopeptidases found in aqueous extracts of a variety of animal tissues. They function optimally within an acidic pH range. The cathepsins occur as a variety of enzyme subtypes including SERINE PROTEASES; ASPARTIC PROTEINASES; and CYSTEINE PROTEASES.	Cathepsin
D002460	Cell Line	Established cell cultures that have the potential to propagate indefinitely.	Cell Lines,Line, Cell,Lines, Cell
D006801	Humans	Members of the species Homo sapiens.	Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D012276	Ricin	A protein phytotoxin from the seeds of Ricinus communis, the castor oil plant. It agglutinates cells, is proteolytic, and causes lethal inflammation and hemorrhage if taken internally.	Castor Bean Lectin,Lectin, Castor Bean,Lectin, Ricinus,Ricin Toxin,RCA 60,RCA60,Ricin A Chain,Ricin B Chain,Ricin D,Ricin I,Ricinus Toxin,A Chain, Ricin,B Chain, Ricin,Ricinus Lectin,Toxin, Ricin,Toxin, Ricinus
D013329	Structure-Activity Relationship	The relationship between the chemical structure of a compound and its biological or pharmacological activity. Compounds are often classed together because they have structural characteristics in common including shape, size, stereochemical arrangement, and distribution of functional groups.	Relationship, Structure-Activity,Relationships, Structure-Activity,Structure Activity Relationship,Structure-Activity Relationships
D046911	Macromolecular Substances	Compounds and molecular complexes that consist of very large numbers of atoms and are generally over 500 kDa in size. In biological systems macromolecular substances usually can be visualized using ELECTRON MICROSCOPY and are distinguished from ORGANELLES by the lack of a membrane structure.	Macromolecular Complexes,Macromolecular Compounds,Macromolecular Compounds and Complexes,Complexes, Macromolecular,Compounds, Macromolecular,Substances, Macromolecular