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Vaccine-derived mutation in motif D of poliovirus RNA-dependent RNA polymerase lowers nucleotide incorporation fidelity.

ABSTRACT: All viral RNA-dependent RNA polymerases (RdRps) have a conserved structural element termed motif D. Studies of the RdRp from poliovirus (PV) have shown that a conformational change of motif D leads to efficient and faithful nucleotide addition by bringing Lys-359 into the active site where it serves as a general acid. The RdRp of the Sabin I vaccine strain has Thr-362 changed to Ile. Such a drastic change so close to Lys-359 might alter RdRp function and contribute in some way to the attenuated phenotype of Sabin type I. Here we present our characterization of the T362I RdRp. We find that the T362I RdRp exhibits a mutator phenotype in biochemical experiments in vitro. Using NMR, we show that this change in nucleotide incorporation fidelity correlates with a change in the structural dynamics of motif D. A recombinant PV expressing the T362I RdRp exhibits normal growth properties in cell culture but expresses a mutator phenotype in cells. For example, the T362I-containing PV is more sensitive to the mutagenic activity of ribavirin than wild-type PV. Interestingly, the T362I change was sufficient to cause a statistically significant reduction in viral virulence. Collectively, these studies suggest that residues of motif D can be targeted when changes in nucleotide incorporation fidelity are desired. Given the observation that fidelity mutants can serve as vaccine candidates, it may be possible to use engineering of motif D for this purpose.

SUBMITTER: Liu X

PROVIDER: S-EPMC3820909 | biostudies-literature | 2013 Nov

REPOSITORIES: biostudies-literature

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Vaccine-derived mutation in motif D of poliovirus RNA-dependent RNA polymerase lowers nucleotide incorporation fidelity.

Liu Xinran X Yang Xiaorong X Lee Cheri A CA Moustafa Ibrahim M IM Smidansky Eric D ED Lum David D Arnold Jamie J JJ Cameron Craig E CE Boehr David D DD

The Journal of biological chemistry 20130930 45

All viral RNA-dependent RNA polymerases (RdRps) have a conserved structural element termed motif D. Studies of the RdRp from poliovirus (PV) have shown that a conformational change of motif D leads to efficient and faithful nucleotide addition by bringing Lys-359 into the active site where it serves as a general acid. The RdRp of the Sabin I vaccine strain has Thr-362 changed to Ile. Such a drastic change so close to Lys-359 might alter RdRp function and contribute in some way to the attenuated ...[more]

PMID: 24085299

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Project description:BackgroundPutative high mutation rates of RNA viruses are believed to mediate undesirable phenomena, such as emergence of drug resistance. However, very little is known about biochemical fidelity rates for viral RNA-dependent RNA polymerases. Using a recently developed in vitro polymerase assay for poliovirus polymerase 3Dpol [Arnold and Cameron (2000) JBC 275:5329], we measured fidelity for each possible mismatch. Polymerase fidelity, in contrast to sequence error rate, is biochemically defined as kpol/Kd of {(correct plus incorrect) divided by incorrect} incorporations, such that a larger value connotes higher fidelity.ResultsTo derive kpol/Kd for correct base incorporation, we performed conventional pre-steady state single turnover measurements, yielding values that range from 0.62 to 9.4 microM-1 sec-1. Pre-steady state measurements for incorrect base incorporation were less straightforward: several anomalous phenomena interfered with data collection. To obtain pre-steady state kinetic data for incorrect base incorporation, three strategies were employed. (1) For some incorrect bases, a conventional approach was feasible, although care was taken to ensure that only single turnovers were being assessed. (2) Heparin or unlabeled RNA traps were used to simulate single turnover conditions. (3) Finally, for some incorrect bases, incorporation was so poor that single datapoints were used to provide kinetic estimates. Overall, we found that fidelity for poliovirus polymerase 3Dpol ranges from 1.2 x 10(4) to 1.0 x 10(6) for transition mutations and 3.2 x 10(5) to 4.3 x 10(7) for transversion mutations.ConclusionThese values are unexpectedly high showing that high RNA virus sequence variation is not due to intrinsically low polymerase fidelity. Based on unusual enzyme behavior that we observed, we speculate that RNA mismatches either directly or indirectly cause enzyme RNA dissociation. If so, high sequence variation of RNA viruses may be due to template-switch RNA recombination and/or unknown fitness/selection phenomena. These findings may lead to a mechanistic understanding of RNA virus error catastrophe and improved anti-viral strategies.

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Vaccine-derived mutation in motif D of poliovirus RNA-dependent RNA polymerase lowers nucleotide incorporation fidelity.

Publications

Vaccine-derived mutation in motif D of poliovirus RNA-dependent RNA polymerase lowers nucleotide incorporation fidelity.

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