Order, dynamics and metal-binding in the lead-dependent ribozyme.

The in vitro selected lead-dependent ribozyme is among the smallest and simplest of the known catalytic RNA motifs and has a unique metal ion specificity for divalent lead. The conformation and dynamics of this ribozyme are analyzed here by NMR and chemical probing experiments. Complete assignments of the 1H, 13C, and 15N resonances have been made, and the NMR chemical shift changes in the presence of Pb2+, Mg2+ or high concentrations of Na+ show that there is no significant structural change upon addition of either activating (Pb2+) or inhibitory (Mg2+) divalent ions. The 13C NMR relaxation data indicate substantial dynamic fluctuations on various time-scales for active-site residues in this ribozyme. The combination of chemical probing and NMR experiments reveals a picture of the active site for the lead-dependent ribozyme that has both ordered and dynamic features.