Uracil DNA Glycosylase Disruption Blocks Ig Gene Conversion and Induces Transition Mutations

Saribasak, Huseyin; Saribasak, Nesibe Nur; Ipek, Fatih M.; Ellwart, Joachim W.; Arima, Hiroshi; Buerstedde, Jean-Marie

doi:10.4049/jimmunol.176.1.365

Cited by 78 publications

(85 citation statements)

References 16 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Although the mechanism of SHM and its target selection is incompletely understood, activation-induced cytidine deaminase (AID) (4,5), which converts cytosine into uracil, for example, in the RGYW motif, initiates SHM by converting a C:G base pair to a U:G mismatch. Removal of the U by uracil-DNA glycosylase (UNG) generates an abasic site in the DNA, which may lead to a variety of base substitutions (6)(7)(8). For the WA motif, it is suggested that after AID-dependent deamination of a cytosine, recognition of the U:G mismatch by mismatch repair protein MutSα (MSH2-MSH6 heterodimer, in which MSH stands for MutS Homolog) leads to the recruitment of DNA polymerase η (Pol η), and with an incision made by UNG the ensuing short-patch repair synthesis results in mutations of A:T pairs to G:C (Fig.…”

Section: π-Cation Stacking | A-to-g Transition | Immunoglobulinmentioning

confidence: 99%

Mechanism of somatic hypermutation at the WA motif by human DNA polymerase η

Zhao

Gregory

Biertumpfel

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

View full text Add to dashboard Cite

Somatic hypermutation is programmed base substitutions in the variable regions of Ig genes for high-affinity antibody generation. Two motifs, RGYW and WA (R, purine; Y, pyrimidine; W, A or T), have been found to be somatic hypermutation hotspots. Overwhelming evidence suggests that DNA polymerase η (Pol η) is responsible for converting the WA motif to WG by misincorporating dGTP opposite the templating T. To elucidate the molecular mechanism, crystal structures and kinetics of human Pol η substituting dGTP for dATP in four sequence contexts, TA, AA, GA, and CA, have been determined and compared. The T:dGTP wobble base pair is stabilized by Gln-38 and Arg-61, two uniquely conserved residues among Pol η. Weak base paring of the W (T:A or A:T) at the primer end and their distinct interactions with Pol η lead to misincorporation of G in the WA motif. Between two WA motifs, our kinetic and structural data indicate that A-to-G mutation occurs more readily in the TA context than AA. Finally, Pol η can extend the T:G mispair efficiently to complete the mutagenesis.

show abstract

Section: π-Cation Stacking | A-to-g Transition | Immunoglobulinmentioning

confidence: 99%

Mechanism of somatic hypermutation at the WA motif by human DNA polymerase η

Zhao

Gregory

Biertumpfel

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

View full text Add to dashboard Cite

show abstract

“…cells, a chicken B-cell line that undergoes SHM in the presence of AID but has limited gene conversion (42). These cells originally express surface IgM and can lose the marker after SHM in the heavy and light chains.…”

Section: Loop Graft Variants Effectively Restrict Hiv-bhagwat and Co-mentioning

confidence: 99%

Local Sequence Targeting in the AID/APOBEC Family Differentially Impacts Retroviral Restriction and Antibody Diversification

Kohli

Maul

Guminski

et al. 2010

Journal of Biological Chemistry

Self Cite

View full text Add to dashboard Cite

Nucleic acid cytidine deaminases of the activation-induced deaminase (AID)/APOBEC family are critical players in active and innate immune responses, playing roles as target-directed, purposeful mutators. AID specifically deaminates the host immunoglobulin (Ig) locus to evolve antibody specificity, whereas its close relative, APOBEC3G (A3G), lethally mutates the genomes of retroviral pathogens such as HIV. Understanding the basis for the target-specific action of these enzymes is essential, as mistargeting poses significant risks, potentially promoting oncogenesis (AID) or fostering drug resistance (A3G). AID prefers to deaminate cytosine in WRC (W ‫؍‬ A/T, R ‫؍‬ A/G) motifs, whereas A3G favors deamination of CCC motifs. This specificity is largely dictated by a single, divergent protein loop in the enzyme family that recognizes the DNA sequence. Through grafting of this substrate-recognition loop, we have created enzyme variants of A3G and AID with altered local targeting to directly evaluate the role of sequence specificity on immune function. We find that grafted loops placed in the A3G scaffold all produced efficient restriction of HIV but that foreign loops in the AID scaffold compromised hypermutation and class switch recombination. Local targeting, therefore, appears alterable for innate defense against retroviruses by A3G but important for adaptive antibody maturation catalyzed by AID. Notably, AID targeting within the Ig locus is proportionally correlated to its in vitro ability to target WRC sequences rather than non-WRC sequences. Although other mechanisms may also contribute, our results suggest that local sequence targeting by AID/APOBEC3 enzymes represents an elegant example of co-evolution of enzyme specificity with its target DNA sequence.

show abstract

“…Mutagenesis observed in DT40 cells appears essentially "passive", occurring by saturation of the uracil-DNA glycosylase (UNG) repair pathway. Accordingly, deletion of Ung in DT40 cells results in a sevenfold increase in mutagenesis 120 , implying that a large fraction of the uracils generated by AID are repaired error-free, by base-excision repair or by sister chromatin exchange. All mutations observed are targeted to G or C bases, being almost exclusively transition mutations or G to C and C to G transversion mutations: they thus appear to be generated during replication by copy of unrepaired uracils or by bypass of abasic sites, performed by Rev1 in a translesion process that appears strictly dependent on PCNA monoubiquitination 121,122 .…”

Section: Box 1 | Shm In the Dt40 Cell Line: "Passive" Versus "Active"mentioning

confidence: 99%

DNA polymerases in adaptive immunity

Weill

Reynaud

2008

Nat Rev Immunol

View full text Add to dashboard Cite

PrefaceTo cope with an unpredictable variety of potential pathogenic insults, the immune system must generate an enormous diversity of recognition structures, and it does so by making stepwise modifications of key genetic loci in each lymphoid cell. This proceeds through the action of lymphoid-specific proteins acting together with the general DNA-repair machinery of the cell. Strikingly, these general mechanisms are usually diverted from their normal functions, being used in rather atypical ways in order to privilege diversity over accuracy. In this Review, we focus on the contribution of a set of DNA polymerases discovered in the last decade to these unique DNA transactions.

show abstract

Uracil DNA Glycosylase Disruption Blocks Ig Gene Conversion and Induces Transition Mutations

Cited by 78 publications

References 16 publications

Mechanism of somatic hypermutation at the WA motif by human DNA polymerase η

Mechanism of somatic hypermutation at the WA motif by human DNA polymerase η

Local Sequence Targeting in the AID/APOBEC Family Differentially Impacts Retroviral Restriction and Antibody Diversification

DNA polymerases in adaptive immunity

Contact Info

Product

Resources

About