2m2v
From Proteopedia
African Swine Fever Virus Pol X in the ternary complex with MgdGTP and DNA
Structural highlights
Function[DPOLX_ASFB7] Error-prone polymerase lacking a proofreading 3'-5' exonuclease which plays a role in viral DNA repair. Specifically binds intermediates in the single-nucleotide base-excision repair process. Also catalyzes DNA polymerization with low nucleotide-insertion fidelity. Together with the viral DNA ligase, fills the single nucleotide gaps generated by the AP endonuclease.[1] [2] Publication Abstract from PubMedA dogma for DNA polymerase catalysis is that the enzyme binds DNA first, followed by MgdNTP. This mechanism contributes to the selection of correct dNTP by Watson-Crick base pairing, but it cannot explain how low-fidelity DNA polymerases overcome Watson-Crick base pairing to catalyze non-Watson-Crick dNTP incorporation. DNA polymerase X from the deadly African swine fever virus (Pol X) is a half-sized repair polymerase that catalyzes efficient dG:dGTP incorporation in addition to correct repair. Here we report the use of solution structures of Pol X in the free, binary (Pol X:MgdGTP), and ternary (Pol X:DNA:MgdGTP with dG:dGTP non-Watson-Crick pairing) forms, along with functional analyses, to show that Pol X uses multiple unprecedented strategies to achieve the mutagenic dG:dGTP incorporation. Unlike high fidelity polymerases, Pol X can prebind purine MgdNTP tightly and undergo a specific conformational change in the absence of DNA. The prebound MgdGTP assumes an unusual syn conformation stabilized by partial ring stacking with His115. Upon binding of a gapped DNA, also with a unique mechanism involving primarily helix alphaE, the prebound syn-dGTP forms a Hoogsteen base pair with the template anti-dG. Interestingly, while Pol X prebinds MgdCTP weakly, the correct dG:dCTP ternary complex is readily formed in the presence of DNA. H115A mutation disrupted MgdGTP binding and dG:dGTP ternary complex formation but not dG:dCTP ternary complex formation. The results demonstrate the first solution structural view of DNA polymerase catalysis, a unique DNA binding mode, and a novel mechanism for non-Watson-Crick incorporation by a low-fidelity DNA polymerase. How a Low-Fidelity DNA Polymerase Chooses Non-Watson-Crick from Watson-Crick Incorporation.,Wu WJ, Su MI, Wu JL, Kumar S, Lim LH, Wang CW, Nelissen FH, Chen MC, Doreleijers JF, Wijmenga SS, Tsai MD J Am Chem Soc. 2014 Mar 21. PMID:24617852[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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