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J. Biol. Chem. 280 (22): 20927-20931

© 2005 by The American Society for Biochemistry and Molecular Biology, Inc.

Disease-associated Mutations Inactivate AMP-Lysine Hydrolase Activity of Aprataxin*



Heather F. Seidle, Pawel Bieganowski, , and Charles Brenner{ddagger}

Departments of Genetics and Biochemistry and Norris Cotton Cancer Center, Dartmouth Medical School, Lebanon, New Hampshire 03756

Abstract: Ataxia-oculomotor apraxia syndrome 1 is an early onset cerebellar ataxia that results from loss of function mutations in the APTX gene, encoding Aprataxin, which contains three conserved domains. The forkhead-associated domain of Aprataxin mediates protein-protein interactions with molecules that respond to DNA damage, but the cellular phenotype of the disease does not appear to be consistent with a major loss in DNA damage responses. Disease-associated mutations in Aprataxin target a histidine triad domain that is similar to Hint, a universally conserved AMP-lysine hydrolase, or truncate the protein NH2-terminal to a zinc finger. With novel fluorigenic substrates, we demonstrate that Aprataxin possesses an active-site-dependent AMP-lysine and GMP-lysine hydrolase activity that depends additionally on the zinc finger for protein stability and on the forkhead associated domain for enzymatic activity. Alleles carrying any of eight recessive mutations associated with ataxia and oculomotor apraxia encode proteins with huge losses in protein stability and enzymatic activity, consistent with a null phenotype. The mild presentation allele, APTX-K197Q, associated with ataxia but not oculomotor apraxia, encodes a protein with a mild defect in stability and activity, while enzyme encoded by the atypical presentation allele, APTX-R199H, retained substantial function, consistent with altered and not loss of activity. The data suggest that the essential function of Aprataxin is reversal of nucleotidylylated protein modifications, that all three domains contribute to formation of a stable enzyme, and that the in vitro behavior of cloned APTX alleles can score disease-associated mutations.

Received for publication March 16, 2005.

* This work was supported by research Grant CA75954 from the NCI, National Institutes of Health. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.


The on-line version of this article (available at contains supplemental Table 1 and Fig. 1.

{diamondsuit} This article was selected as a Paper of the Week.

{ddagger} To whom correspondence should be addressed: Norris Cotton Cancer Center, Dartmouth Medical School, Rubin 733-HB7937, Lebanon, NH 03756. Tel.: 603-653-9922; Fax: 603-653-9923; E-mail: charles.brenner{at}

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