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Updated: Aug 3, 2026

Isolation of Translating Ribosomes Containing Peptidyl-tRNAs for Functional and Structural Analyses
Published on: February 25, 2011
Microenvironment of cysteine 242 in type-1 ribosome-inactivating protein from iris
Q Hao1, E J Van Damme, A Barre
1Laboratory of Phytopathology and Plant Protection, Katholieke Universiteit Leuven, Willem de Croylaan 42, Leuven, 3001, Belgium.
Abstract:
IRIP is a type-1 ribosome-inactivating protein isolated from the bulbs of Iris hollandica. It is one of the few type-1 RIPs that contain Cys residue(s) in their primary sequence. IRIP contains a single Cys residue at position 242. Although IRIP is thought to be a monomeric protein, SDS-PAGE indicates that part of the IRIP molecules can exist as disulphide bridge-linked dimers. Probing of the reactivity of the unique Cys residue by 5, 5'-dithiobis(2-nitrobenzoic acid) indicates that Cys(242) in IRIP is free but is only partially accessible to modifiers. Molecular modelling of IRIP is in agreement with this conclusion. Binding of the ligands adenine and poly(A) results in little or no effect on the conformation of Cys(242) in IRIP. Chemical modification of IRIP by a specific thiol modifier does not abolish the RNA N-glycosidase activity of IRIP, suggesting that Cys(242) is not critical for the enzymatic activity of IRIP. These results suggest that IRIP has the potential to be developed as a novel immunotoxin.
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