Mechanism of somatic hypermutation at the WA motif by human DNA polymerase eta
【摘要】：Somatic hypermutation(SHM) is programmed base substitutions in the variable regions of immunoglobulin genes for high-affinity antibody generation. Two motifs, RGYW and WA(R=purine, Y=pyrimidine, W=A or T), have been found to be SHM hotspots. Overwhelming evidence suggests that DNA polymerase 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 Gln38 and Arg61, 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. TA is more mutable than AA. Finally, Pol η can extend the T:G mispair efficiently to complete the mutagenesis.