PMID: 24694247
Koag MC, Lee S
Metal-Dependent Conformational Activation Explains Highly Promutagenic Replication across O6-Methylguanine by Human DNA Polymerase beta
J Am Chem Soc. 2014 Apr 2.
Human DNA polymerase beta (polbeta) inserts, albeit slowly, T opposite the carcinogenic lesion O6-methylguanine (O6MeG) approximately 30-fold more frequently than C. To gain insight into this promutagenic process, we solved four ternary structures of polbeta with an incoming dCTP or dTTP analogue base-paired with O6MeG in the presence of active-site Mg2+ or Mn2+. The Mg2+-bound structures show that both the O6MeG.dCTP/dTTP-Mg2+ complexes adopt an open protein conformation, staggered base pair, and one active-site metal ion. The Mn2+-bound structures reveal that, whereas the O6Me.dCTP-Mn2+ complex assumes the similar altered conformation, the O6MeG.dTTP-Mn2+ complex adopts a catalytically competent state with a closed protein conformation and pseudo-Watson-Crick base pair. On the basis of these observations, we conclude that polbeta slows nucleotide incorporation opposite O6MeG by inducing an altered conformation suboptimal for catalysis and promotes mutagenic replication by allowing Watson-Crick-mode for O6MeG.T but not for O6MeG.C in the enzyme active site. The O6MeG.dTTP-Mn2+ ternary structure, which represents the first structure of mismatched polbeta ternary complex with a closed protein conformation and coplanar base pair, the first structure of pseudo-Watson-Crick O6MeG.T formed in the active site of a DNA polymerase, and a rare, if not the first, example of metal-dependent conformational activation of a DNA polymerase, indicate that catalytic metal-ion coordination is utilized as a kinetic checkpoint by polbeta and is crucial for the conformational activation of polbeta. Overall, our structural studies not only explain the promutagenic polbeta catalysis across O6MeG but also provide new insights into the replication fidelity of polbeta.