Lincoln Scott - An active-site guanine participates in glmS ribozyme catalysis in its protonated state.

Document created by Lincoln Scott on Aug 22, 2014
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  J Am Chem   Soc. 2011 Nov 16;133(45):18388-96. doi:   10.1021/ja207426j. Epub 2011 Oct 20.


  Active-site guanines that occupy similar positions have been   proposed to serve as general base catalysts in hammerhead,   hairpin, and glmS ribozymes, but no specific roles for these   guanines have been demonstrated conclusively. Structural studies   place G33(N1) of the glmS ribozyme of Bacillus anthracis within   hydrogen-bonding distance of the 2'-OH nucleophile. Apparent   pK(a) values determined from the pH dependence of cleavage   kinetics for wild-type and mutant glmS ribozymes do not support a   role for G33, or any other active-site guanine, in general base   catalysis. Furthermore, discrepancies between apparent pK(a)   values obtained from functional assays and microscopic pK(a)   values obtained from pH-fluorescence profiles with ribozymes   containing a fluorescent guanosine analogue, 8-azaguanosine, at   position 33 suggest that the pH-dependent step in catalysis does   not involve G33 deprotonation. These results point to an   alternative model in which G33(N1) in its neutral, protonated   form donates a hydrogen bond to stabilize the transition state.

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