Structural explanation for the role of Mn^2+ in the activity of Φ6 RNA-dependent RNA polymerase

The biological role of manganese (MN^2+) has been a long-standing puzzle, since at low concentrations it activates several polymerases whilst at higher concentrations it inhibits. Viral RNA polymerases possess a common architecture, reminiscent of a closed right hand. The RNA-dependent RNA polymerase (RdRp) of bacteriophage Φ6 is one of the best understood examples of this important class of polymerases. We have probed the role of MN^2+ by biochemical, biophysical and structural analyses of the wild-type enzyme and of a mutant form with an altered Mn^2+ -binding site (E491 to Q). The E491Q mutant has much reduced affinity for Mn^2+, reduced RNA binding and a compromised elongation rate. Loss of Mn^2+ binding structurally stabilizes the enzyme. These data and a re-examination of the structures of other viral RNA polymerases clarify the role of manganese in the activation of polymerization: Mn^2+ coordination of a catalytic aspartate is necessary to allow the active site to properly engage with the triphosphates of the incoming NTPs. The structural flexibility caused by Mn^2+ is also important for the enzyme dynamics, explaining the requirement for manganese throughout RNA polymerization.Citation: Poranen, M. M. et al. (2008). 'Structural explanation for the role of Mn^2+ in the activity of Φ6 RNA-dependent RNA polymerase', Nucleic Acids Research, 36(20), 6633-6644. [Available at http://nar.oxfordjournals.org/]. This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited