[Show abstract][Hide abstract] ABSTRACT: Double-stranded RNA viruses encode a single protein species containing RNA-dependent RNA polymerase (RdRP) motifs. This protein is responsible for RNA transcription and replication. The architecture of viral RdRPs resembles that of a cupped right hand with fingers, palm and thumb domains. Those using de novo initiation have a flexible structural elaboration that constitutes the priming platform. Here we investigate the properties of the C-terminal priming domain of bacteriophage ϕ6 to get insights into the role of an extended loop connecting this domain to the main body of the polymerase. Proteolyzed ϕ6 RdRP that possesses a nick in the hinge region of this loop was better suited for de novo initiation. The clipped C-terminus remained associated with the main body of the polymerase via the anchor helix. The structurally flexible hinge region appeared to be involved in the control of priming platform movement. Moreover, we detected abortive initiation products for a bacteriophage RdRP.
[Show abstract][Hide abstract] ABSTRACT: RNA-dependent RNA polymerases (RdRps) are key to the replication of RNA viruses. A common divalent cation binding site, distinct
from the positions of catalytic ions, has been identified in many viral RdRps. We have applied biochemical, biophysical, and
structural approaches to show how the RdRp from bacteriophage ϕ6 uses the bound noncatalytic Mn2+ to facilitate the displacement of the C-terminal domain during the transition from initiation to elongation. We find that
this displacement releases the noncatalytic Mn2+, which must be replaced for elongation to occur. By inserting a dysfunctional Mg2+ at this site, we captured two nucleoside triphosphates within the active site in the absence of Watson-Crick base pairing
with template and mapped movements of divalent cations during preinitiation. These structures refine the pathway from preinitiation
through initiation to elongation for the RNA-dependent RNA polymerization reaction, explain the role of the noncatalytic divalent
cation in ϕ6 RdRp, and pinpoint the previously unresolved Mn2+-dependent step in replication.
Full-text · Article · Dec 2011 · Journal of Virology
[Show abstract][Hide abstract] ABSTRACT: 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 6 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.
Full-text · Article · Nov 2008 · Nucleic Acids Research