PMID: 26473980

Authors:

Kosutic M, Neuner S, Ren A, Flur S, Wunderlich C, Mairhofer E, Vusurovic N, Seikowski J, Breuker K, Hobartner C, Patel DJ, Kreutz C, Micura R

Title:

A Mini-Twister Variant and Impact of Residues/Cations on the Phosphodiester Cleavage of this Ribozyme Class.

Journal:

Angew Chem Int Ed Engl. 2015 Dec 7;54(50):15128-33. doi: 10.1002/anie.201506601. , Epub 2015 Oct 16.

Abstract:

Nucleolytic ribozymes catalyze site-specific cleavage of their phosphodiester backbones. A minimal version of the twister ribozyme is reported that lacks the phylogenetically conserved stem P1 while retaining wild-type activity. Atomic mutagenesis revealed that nitrogen atoms N1 and N3 of the adenine-6 at the cleavage site are indispensable for cleavage. By NMR spectroscopy, a pKa value of 5.1 was determined for a (13) C2-labeled adenine at this position in the twister ribozyme, which is significantly shifted compared to the pKa of the same adenine in the substrate alone. This finding pinpoints at a potential role for adenine-6 in the catalytic mechanism besides the previously identified invariant guanine-48 and a Mg(2+) ion, both of which are directly coordinated to the non-bridging oxygen atoms of the scissile phosphate; for the latter, additional evidence stems from the observation that Mn(2+) or Cd(2+) accelerated cleavage of phosphorothioate substrates. The relevance of this metal ion binding site is further emphasized by a new 2.6 A X-ray structure of a 2'-OCH3 -U5 modified twister ribozyme.