Mapping of the interaction interface of DNA polymerase β with XRCC1

Residues of DNA polymerase beta (beta-Pol) that interact with the DNA repair protein XRCC1 have been determined by NMR chemical shift mapping (CSM) and mutagenesis. N-15/C-13/H-2/H-1,C-13-methyl(Leu,Ile,Val)-labeled beta-Pol palm-thumb domain was used for assignments of the H-1, N-15, and C-13 resonances used for CSM of the palm-thumb on forming the 40 kDa complex with the XRCC1 N-terminal domain (NTD). Large chemical shift changes were observed in the thumb on complexation. N-15 relaxation data indicate reduction in high-frequency motion for a thumb loop and three palm turn/loops, which showed concomitant chemical shift changes on complexation. A DeltaV303-V306 deletion and an L301R/V303R/V306R triple mutation abolished complex formation due to loss in hydrophobicity. In an updated model, the thumb-loop of beta-Pol contacts an edge/face region of the beta sheet of the XRCC1 NTD, while the beta-Pol palm weakly contacts the alpha2 helix.