Mapping of the Interaction Interface of DNA Polymerase β with XRCC1

Abstract

Residues of DNA polymerase β (β-Pol) that interact with the DNA repair protein XRCC1 have been determined by NMR chemical shift mapping (CSM) and mutagenesis. 15N/ 13C/ 2H/ 1H, 13C-methyl Leu,Ile,Val-labeled β-Pol palm-thumb domain was used for assignments of the 1H, 15N, and 13C 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. 15N 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 ΔV303–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 β-Pol contacts an edge/face region of the β sheet of the XRCC1 NTD, while the β-Pol palm weakly contacts the α2 helix.