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

ABSTRACT: 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 ? (Pol ?) 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 ? 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 ?. Weak base paring of the W (T:A or A:T) at the primer end and their distinct interactions with Pol ? 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 ? can extend the T:G mispair efficiently to complete the mutagenesis.

SUBMITTER: Zhao Y 

PROVIDER: S-EPMC3657764 | biostudies-literature | 2013 May

REPOSITORIES: biostudies-literature