Protonation-Dependent Base Flipping at Neutral pH in the Catalytic Triad of a Self-Splicing Bacterial GroupII Intron

• Published in: Angewandte Chemie International Edition 2015-08, Vol.54 (33), p.9687-9690
• Main Authors: Pechlaner, Maria, Donghi, Daniela, Zelenay, Veronika, Sigel, Roland KO
• Format: Article
• Language: English
• Subjects: Adenines; Assembly; Bacteria; Catalysis; Catalysts; Crystal structure; NMR spectroscopy; Splicing
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201504014

NMR spectroscopy has revealed pH-dependent structural changes in the highly conserved catalytic domain5 of a bacterial groupII intron. Two adenines with pK sub(a) values close to neutral pH were identified in the catalytic triad and the bulge. Protonation of the adenine opposite to the catalytic triad is stabilized within a G(syn)-AH super(+)(anti) base pair. The pH-dependent anti-to-syn flipping of this G in the catalytic triad modulates the known interaction with the linker region between domains2 and 3 (J23) and simultaneously the binding of the catalytic Mg super(2+) ion to its backbone. Hence, this here identified shifted pK sub(a) value controls the conformational change between the two steps of splicing. Strongly shifted: Two adenines in the highly conserved and catalytically essential domain5 of groupII introns become protonated near physiological pHvalues. The associated dynamic equilibria play an important role in groupII intron assembly and catalysis.