The R215W mutation in NBS1 impairs gamma-H2AX binding and affects DNA repair: molecular bases for the severe phenotype of 657del5/R215W Nijmegen breakage syndrome patients.

Nijmegen breakage syndrome (NBS) is a genetic disorder characterized by chromosomal instability and hypersensitivity to ionising radiation. Compound heterozygous 657del5/R215W NBS patients display a clinical phenotype more severe than the majority of NBS patients homozygous for the 657del5 mutation. The NBS1 protein, mutated in NBS patients, contains a FHA/BRCT domain necessary for the DNA-double strand break (DSB) damage response. Recently, a second BRCT domain has been identified, however, its role is still unknown. Here, we demonstrate that the R215W mutation in NBS1 impairs histone gamma-H2AX binding after induction of DNA damage, leading to a delay in DNA-DSB rejoining. Molecular modelling reveals that the 215 residue of NBS1 is located between the two BRCT domains, affecting their relative orientation that appears critical for gamma-H2AX binding. Present data represent the first evidence for the role of NBS1 tandem BRCT domains in gamma-H2AX recognition, and could explain the severe phenotype observed in 657del5/R215W NBS patients.