Search for: All records

Background: MutY initiated base excision repair (BER) protects against mutations that otherwise result from oxidative damage to guanine. The 8-oxo-7,8-dihydro-guanine lesion (OG) pairs equally well with C or A, a source of ambiguity that explains high rates of GC → TA mutations for biallelic defects in the gene encoding MUTYH in humans. MutY/MUTYH intercepts the A:OG lesion and removes the chemically correct but informationally defective adenine nucleobase. A catalytic Glu – Glu43 in Geobacillus stearothermophilus MutY (Gs MutY); Glu37 in Escherichia coli MutY (Ec MutY); Glu134 in human MUTYH – is a defining chemical motif for A:OG adenine DNA glycosylases that is not found in other helix-hairpin-helix family members. While the importance of Glu for MutY’s catalytic mechanism is well understood, its origin is unknown. Discovery: Here we tested the structural and kinetic consequences of Glu replacement and found an alternate, slower mechanism, that yields a different stereoisomer for the AP site product. The impact on catalytic rate was consistent removal of acid/base catalysis and retention of transition state stabilization. High-resolution structures for E43Q and E43S substitution variants of Gs MutY show substrate disengagement and the enzyme-generated AP product in its alpha-anomer configuration. These results suggest that acquisition of Glu was a key innovation for emergence of the MutY/MUTYH lineage from an ancestral DNA glycosylase.