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Active site labeling of G8 in the hairpin ribozyme: Implications for structure and mechanism

TitleActive site labeling of G8 in the hairpin ribozyme: Implications for structure and mechanism
Publication TypeJournal Article
Year of Publication2006
AuthorsThomas, JM, Perrin, DM
JournalJournal of the American Chemical Society
Volume128
Pagination16540-16545
Date PublishedDec
ISBN Number0002-7863
Abstract

There is mounting evidence that suggests that general acid/base catalysis is operative in the hairpin ribozyme, with analogy to the protein enzyme RNaseA. Nevertheless, the extent of general base catalysis as well as the identity of the specific chemical groups responsible remains the subject of some controversy. An affinity label has previously been used to alkylate histidine 12 (His12), the active general base in RNaseA. To date, no such experiment has been applied to a ribozyme. We have synthesized the analogous affinity label for the hairpin ribozyme with an electrophilic 2’-bromoacetamide group in lieu of the 2’-hydroxyl (2’OH) at the substrate cleavage site and show that guanosine 8 (G8) of the hairpin ribozyme is specifically alkylated, most likely at the N1 position. This evidence strongly implicates N1 of G8 in active site chemistry. By direct analogy to RNase A, these findings could be consistent with the hypothesis that deprotonated G8 residue functions as a general base in the hairpin ribozyme. Other mechanistic possibilities for N1 of G8 such as indirect general base catalysis mediated by a water molecule or transition state stabilization could also be consistent with our findings.

URL<Go to ISI>://000242941600058