Characterisation of Archaeglobus fulgidus AlkA hypoxanthine DNA glycosylase activity

The AlkA protein from the archaebacterium Archaeglobus fulgidus was characterised with respect to release of hypoxanthine from DNA. The hypoxanthine glycosylase activity had optimal activity at 60°C at pH 5.0. The enzyme released hypoxanthine from substrates with a preference for dI:dG≫dI:dT>dI:dC>dI:dA. The presence of a mismatch on either side of the dIMP in the substrate reduced excision efficiency of the hypoxanthine residue at neutral pH, while a mismatch on both sides of the dIMP resulted in total loss of excision. Release of hypoxanthine from DNA required a minimum of two bases on the 5′ side and four bases on the 3′ side of the dIMP residue.