Nucleic Acids Research Advance Access published online on October 21, 2008
Nucleic Acids Research, doi:10.1093/nar/gkn632
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Structural Biology |
Structural explanation for the role of Mn2+ in the activity of 
6 RNA-dependent RNA polymerase
1Institute of Biotechnology and Department of Biological and Environmental Sciences, Viikki Biocenter, P.O. Box 56 (Viikinkaari 5) 00014 University of Helsinki, Finland and 2Division of Structural Biology, The Henry Wellcome Building for Genomic Medicine, Oxford University, Roosevelt Drive, Oxford OX3 7BN, UK
*To whom Correspondence should be addressed. Tel: +44 1865 287561; Fax: +44 1865 287547; Email: jonathan{at}strubi.ox.ac.uk
Received November 13, 2007. Revised September 9, 2008. Accepted September 13, 2008.
The biological role of manganese (Mn2+) 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 
6 is one of the best understood examples of this important class of polymerases. We have probed the role of Mn2+ by biochemical, biophysical and structural analyses of the wild-type enzyme and of a mutant form with an altered Mn2+-binding site (E491 to Q). The E491Q mutant has much reduced affinity for Mn2+, reduced RNA binding and a compromised elongation rate. Loss of Mn2+ 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: Mn2+ 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 Mn2+ is also important for the enzyme dynamics, explaining the requirement for manganese throughout RNA polymerization.
Present address: Paula S. Salgado, Division of Molecular Biosciences, Faculty of Life Sciences, Imperial College London, South Kensington Campus, Exhibition Road, London SW7 2AZ, UK.
The authors wish it to be known that, in their opinion, the first two authors should be regarded as joint First Authors.
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