Ataxia with oculomotor apraxia type 1 (AOA1) is an early onset autosomal recessive
spinocerebellar ataxia with a defect in the
protein Aprataxin, implicated in the response of cells to DNA damage. We describe here the expression of a recombinant form of Aprataxin and show that it has dual
DNA binding and
nucleotide hydrolase activities. This
protein binds to
double-stranded DNA with high affinity but is also capable of binding
double-stranded RNA and single-strand
DNA, with increased affinity for hairpin structures. No increased binding was observed with a variety of
DNA structures mimicking intermediates in DNA repair. The
DNA binding observed here was not dependent on
zinc, and the addition of exogenous
zinc abolished
DNA binding. We also demonstrate that Aprataxin hydrolyzes with similar efficiency the model
histidine triad
nucleotide-
binding protein substrate, AMPNH2, and the
Fragile histidine triad protein substrate,
Ap4A. These activities were significantly reduced in the presence of duplex
DNA and to a lesser extent in the presence of single-strand
DNA, and removal of the N-terminal Forkhead associated domain did not alter activity. Finally, comparison of sequence relationships between the
histidine triad superfamily members shows that Aprataxin forms a distinct branch in this superfamily. In addition to its capacity for
nucleotide binding and hydrolysis, the observation that it also binds
DNA and
RNA adds a new dimension to this superfamily of
proteins and provides further support for a role for Aprataxin in the cellular response to DNA damage.