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adenosine-5'-diphospho-5'-(ribonucleotide)-[DNA] + H2O = AMP + 5'-phospho-(ribonucleotide)-[DNA]
adenosine-5'-diphospho-5'-[DNA] + H2O = AMP + phospho-5'-[DNA]
adenosine-5'-diphospho-5'-(ribonucleotide)-[DNA] + H2O = AMP + 5'-phospho-(ribonucleotide)-[DNA]
a two-step mechanism for hydrolysis of 5'-AMP from RNA-DNA and DNA, APTX catalytic mechanism, overview. In the first step, the active site nucleophile (His260 of the HIT loop in APTX) attacks the 5'-adenylate phosphoanhydride forming a transient enzyme-AMP intermediate and releasing a DNA vphosphate product. Several hydrogen bonds with active-site residues and peptide backbone amides stabilize the negative charge on the transitin-state of step 1. The nucleophile (His260) is activated by a hydrogen bond to the carbonyl of His258, while His251 is proposed to protonate the 5'-phosphate leaving group. The second step involves hydrolysis of the His260-AMP-RNA/DNA intermediate, using chemistry that is essentially the reverse of the first step with water replacing the 5'-phosphate, and with His251 proposed to act as a general base to deprotonate a water nucleophile
adenosine-5'-diphospho-5'-(ribonucleotide)-[DNA] + H2O = AMP + 5'-phospho-(ribonucleotide)-[DNA]
the catalytic reaction proceeds in three steps: substrate protonation, DNA deadenylation and histidine-AMP intermediate hydrolysis. The calculated activation energies for the second and third reactions are 19.0 and 10.5 kcal/mol, which can be attributed to a penta-coordinated AMP-phosphoryl formation and closing of a water molecule, respectively. A histidine-AMP intermediate is hydrolyzed easily in the third step when a water molecule closes within 3 A to the phosphorus nucleus
adenosine-5'-diphospho-5'-(ribonucleotide)-[DNA] + H2O = AMP + 5'-phospho-(ribonucleotide)-[DNA]
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adenosine-5'-diphospho-5'-[DNA] + H2O = AMP + phospho-5'-[DNA]
a two-step mechanism for hydrolysis of 5'-AMP from RNA-DNA and DNA, APTX catalytic mechanism, overview. In the first step, the active site nucleophile (His260 of the HIT loop in APTX) attacks the 5'-adenylate phosphoanhydride forming a transient enzyme-AMP intermediate and releasing a DNA 5'-phosphate product. Several hydrogen bonds with active-site residues and peptide backbone amides stabilize the negative charge on the transition-state of step 1. The nucleophile (His260) is activated by a hydrogen bond to the carbonyl of His258, while His251 is proposed to protonate the 5'-phosphate leaving group. The second step involves hydrolysis of the His260-AMP-RNA/DNA intermediate, using chemistry that is essentially the reverse of the first step with water replacing the 5'-phosphate, and with His251 proposed to act as a general base to deprotonate a water nucleophile
adenosine-5'-diphospho-5'-[DNA] + H2O = AMP + phospho-5'-[DNA]
the catalytic reaction proceeds in three steps: substrate protonation, DNA deadenylation and histidine-AMP intermediate hydrolysis. The calculated activation energies for the second and third reactions are 19.0 and 10.5 kcal/mol, which can be attributed to a penta-coordinated AMP-phosphoryl formation and closing of a water molecule, respectively. A histidine-AMP intermediate is hydrolyzed easily in the third step when a water molecule closes within 3 A to the phosphorus nucleus
adenosine-5'-diphospho-5'-[DNA] + H2O = AMP + phospho-5'-[DNA]
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evolution
aprataxin (APTX) belongs to a family of histidine triad (HIT) enzymes. Mutation of His138 to alanine does not completely abolish the catalytic activity; the residual activity is 25% of the wild-type enzyme activity. The DNA deadenylation reaction catalyzed by the H138A mutant can proceed by the protonated substrate
malfunction
APTX human mutations cause the neurodegenerative disorder ataxia with oculomotor ataxia 1 (AOA1). AOA1 mutagenic effects on APTX solubility, stability, and catalytic activity, and molecular basis for APTX inactivation in AOA1, APTX mutations variably impact protein folding and activity, overview
malfunction
ataxia oculomotor apraxia-1 (AOA1) is a recessive human neurodegenerative disorder linked to more than 20 distinct mutations in the gene encoding APTX. Although reminiscent of ataxia-telangiectasia, primary AOA1 fibroblasts exhibit only mild hypersensitivity to ionizing radiation
malfunction
lack of aprataxin impairs mitochondrial functions, independent of its role in mitochondrial DNA repair, via downregulation of the APE1/NRF1/NRF2 pathway. Ataxia oculomotor apraxia type 1 (AOA1) is an autosomal recessive disease caused by mutations in APTX, which encodes the DNA strand-break repair protein aprataxin (APTX). CoQ10 deficiency is identified in fibroblasts and muscle of AOA1 patients carrying the common W279X mutation, and aprataxin has been localized to mitochondria in neuroblastoma cells, where it enhances preservation of mitochondrial function. The bioenergetics defect in AOA1-mutant fibroblasts and APTX-depleted Hela cells is caused by decreased expression of SDHA and genes encoding CoQ biosynthetic enzymes, in association with reductions of APE1, NRF1 and NRF2. APE1 depletion impairs NRF1 expression in Hela cells and resembles APTX knockdown clones, mitochondrial genes are downregulated in APE1-deficient cells owing to the regulatory role of APE1 on DNA-binding and transcriptional activity of NRF1
malfunction
mutation of aprataxin (APTX) is causing the heritable neurological disorder ataxia with oculomotor apraxia 1 (AOA1)
malfunction
mutations of the APTX gene cause neurological diseases such as ataxia oculomotor aparaxia type 1 (AOA1)
malfunction
while hnt3DELTA single mutants are not sensitive to DNA damaging agents, loss of HNT3 causes synergistic sensitivity to H2O2 in backgrounds that accumulate strand breaks with blocked termini, including apn1DELTA/apn2DELTA/tpp1DELTA and ntg1DELTA/ntg2DELTA/ogg1DELTA. Loss of HNT3 in rad27DELTA cells, which are deficient in long-patch base excision repair (LP-BER), results in synergistic sensitivity to H2O2 and methylmethane sulfonate, indicating that Hnt3 and LP-BER provide parallel pathways for processing 5'-AMPs. Loss of HNT3 also increases the sister chromatid exchange frequency. HNT3 deletion partially rescues H2O2 sensitivity in recombination deficient rad51DELTA and rad52DELTA cells, suggesting that Hnt3 promotes formation of a repair intermediate that is resolved by recombination. Expression of Myc-NLS-tagged human aprataxin from a plasmid complements HNT3 deletion
physiological function
5'-AMP DNA hydrolysis of aprataxin, energy profile of the APTX catalytic reaction and the protonate states, by quantum mechanical/molecular mechanical (QM/MM) calculations and modeling, overview. Aprataxin hydrolyses abnormal 5'-AMP DNA termini formed in abortive DNA ligations, it is an important DNA repair enzyme
physiological function
aprataxin (APTX) is a DNA-adenylate hydrolase that removes 5'-AMP blocking groups from abortive ligation repair intermediates. Primary role of aprataxin is processing of adenylated 5' ends. XRCC1, a multi-domain protein without catalytic activity, interacts with a number of known repair proteins including APTX, modulating and coordinating the various steps of DNA repair. CK2- phosphorylation of XRCC1 is thought to be crucial for its interaction with the FHA domain of APTX. A phosphorylated XRCC1 is required for APTX recruitment.No interaction of APTX with a phosphorylation mutant of XRCC1
physiological function
critical role of APTX in transcription regulation of mitochondrial function and the pathogenesis of AOA1 via a novel pathomechanistic pathway, which may be relevant to other neurodegenerative diseases
physiological function
eukaryotic DNA ligases seal DNA breaks in the final step of DNA replication and repair transactions via a three-step reaction mechanism that can abort if DNA ligases encounter modified DNA termini, such as the products and repair intermediates of DNA oxidation, alkylation, or the aberrant incorporation of ribonucleotides into genomic DNA. Such abortive DNA ligation reactions create 5'-adenylated nucleic acid termini in the context of DNA and RNA-DNA substrates in DNA base excision repair (BER), double strand break repair (DSBR) and ribonucleotide excision repair (RER). Aprataxin (APTX), a protein altered in the heritable neurological disorder ataxia with oculomotor apraxia 1 (AOA1), acts as a DNA ligase proofreader to directly reverse AMP-modified nucleic acid termini in DNA- and RNA-DNA damage response, molecular mechanism, overview. Elongation of the wedge helix enables dynamic interactions with both the AMP lesion and the exposed base stack on the 5'-end of the damaged DNA strand. The second major DNA binding interface involves undamaged DNA strand binding by the Znf domain
physiological function
Hnt3 promotes formation of a repair intermediate that is resolved by recombination. Hnt3 and LP-BER provide parallel pathways for processing 5'-AMPs, and Hnt3 promotes formation of a repair intermediate that is resolved by recombination. Lack of evidence for Hnt3 involvement in nonhomologous end joining
physiological function
the APTX RNA-DNA deadenylase protects genome integrity and corrects abortive DNA ligation arising during ribonucleotide excision repair and base excision DNA repair, APTX nicked DNA sensing and pleiotropic inactivation in neurodegenerative disease, mechanism
additional information
active site structure of APTX, and molecular reaction mechanism, modeling, overview. General acid-base catalysis of APTX with and important role of His138 as a general acid. The second step, the histidine-AMP intermediate hydrolysis, can proceed with the aid of the product DNA phosphate without a general base residue
additional information
two highly conserved amino acid sequence motifs typify the HIT-Znf region of APTX. The first is the histidine triad motif HXHXHXX (X = hydrophobic residue) of the HIT domain, and the second is a C-terminal Zn-binding (Znf) domain with a sequence motif C(x2)C(x11-12)H(x3)H/E (x = any amino acid). This core HIT-Znf architecture is conserved in APTX orthologs with bona-fide polynucleotide adenylate hydrolase activity including plant, yeast and vertebrate homologues, suggesting that the Znf domain imparts critical substrate specificity to the aprataxins. The APTX Zn2+-binding betabetaalpha core is structurally related to the ubiquitous family of DNA binding C2H2 transcription factors including the prototypical Zif268. APTX Zn2+ ligands can be of either the C2H2 (Cys2-His2 in vertebrate APTX) or C2HE (Cys2-His-Glu in fungal Aptx), which both fold into very similar DNA damage recognition elements
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A198V/P206L
site-directed mutagenesis, a mutation causing the neurodegenerative disorder ataxia with oculomotor ataxia 1 (AOA1)
D267G/W279X
site-directed mutagenesis, a mutation causing the neurodegenerative disorder ataxia with oculomotor ataxia 1 (AOA1)
G231E/689insT
site-directed mutagenesis, a mutation causing the neurodegenerative disorder ataxia with oculomotor ataxia 1 (AOA1)
H138A
site-directed mutagenesis, mutation of His138 to alanine does not completely abolish the catalytic activity, the residual activity is 25% of the wild-type enzyme activity. The DNA deadenylation reaction catalyzed by the H138A mutant can proceed by the protonated substrate
K197Q/W279X
site-directed mutagenesis, a mutation causing the neurodegenerative disorder ataxia with oculomotor ataxia 1 (AOA1)
P206L
naturally occuring mutation predicted to affect protein stability by destabilizing or truncating the folded core of APTX, catalytically inactive mutant
R199H
site-directed mutagenesis, a mutation causing the neurodegenerative disorder ataxia with oculomotor ataxia 1 (AOA1)
R306X/W279X
site-directed mutagenesis, a mutation causing the neurodegenerative disorder ataxia with oculomotor ataxia 1 (AOA1)
S242N
site-directed mutagenesis, a mutation causing the neurodegenerative disorder ataxia with oculomotor ataxia 1 (AOA1)
V263G/P206L
site-directed mutagenesis, a mutation causing the neurodegenerative disorder ataxia with oculomotor ataxia 1 (AOA1)
W279R/IVS5
site-directed mutagenesis, a mutation causing the neurodegenerative disorder ataxia with oculomotor ataxia 1 (AOA1)
W279X/I159fs
site-directed mutagenesis, a mutation causing the neurodegenerative disorder ataxia with oculomotor ataxia 1 (AOA1)
W279X/Q181X
site-directed mutagenesis, a mutation causing the neurodegenerative disorder ataxia with oculomotor ataxia 1 (AOA1)
W279X/R306X
site-directed mutagenesis, a mutation causing the neurodegenerative disorder ataxia with oculomotor ataxia 1 (AOA1)
A198V
naturally occuring mutation predicted to affect protein stability by destabilizing or truncating the folded core of APTX, catalytically inactive mutant
A198V
site-directed mutagenesis, a mutation causing the neurodegenerative disorder ataxia with oculomotor ataxia 1 (AOA1)
D185E
naturally occuring mutation predicted to affect protein stability by destabilizing or truncating the folded core of APTX
D185E
site-directed mutagenesis, a mutation causing the neurodegenerative disorder ataxia with oculomotor ataxia 1 (AOA1)
D267G
naturally occuring mutation predicted to affect protein stability by destabilizing or truncating the folded core of APTX, catalytically inactive mutant
D267G
site-directed mutagenesis, a mutation causing the neurodegenerative disorder ataxia with oculomotor ataxia 1 (AOA1)
G231E
naturally occuring mutation predicted to affect protein stability by destabilizing or truncating the folded core of APTX, catalytically inactive mutant
G231E
site-directed mutagenesis, a mutation causing the neurodegenerative disorder ataxia with oculomotor ataxia 1 (AOA1)
H201Q
naturally occuring active site mutation, the mutant displays impaired AMP-lysine hydrolase activity
H201Q
site-directed mutagenesis, a mutation causing the neurodegenerative disorder ataxia with oculomotor ataxia 1 (AOA1)
H201R
naturally occuring active site mutation, the mutant displays impaired AMP-lysine hydrolase activity
H201R
site-directed mutagenesis, a mutation causing the neurodegenerative disorder ataxia with oculomotor ataxia 1 (AOA1)
K197Q
naturally occuring mutation, the mutant displays impaired AMP-lysine hydrolase activity, confers a late onset neurological disease AOA1
K197Q
site-directed mutagenesis, a mutation causing the neurodegenerative disorder ataxia with oculomotor ataxia 1 (AOA1)
L223P
naturally occuring mutation predicted to affect protein stability by destabilizing or truncating the folded core of APTX, catalytically inactive mutant
L223P
site-directed mutagenesis, a mutation causing the neurodegenerative disorder ataxia with oculomotor ataxia 1 (AOA1)
L248M
naturally occuring dominant mutation in APTX
L248M
site-directed mutagenesis, a mutation causing the neurodegenerative disorder ataxia with oculomotor ataxia 1 (AOA1)
R247X
naturally occuring mutation predicted to affect protein stability by destabilizing or truncating the folded core of APTX, catalytically inactive mutant
R247X
site-directed mutagenesis, not involved in AOA1 disease
R306X
naturally occuring mutation predicted to affect protein stability by destabilizing or truncating the folded core of APTX, catalytically inactive mutant
R306X
site-directed mutagenesis, a mutation causing the neurodegenerative disorder ataxia with oculomotor ataxia 1 (AOA1)
V263G
naturally occuring mutation predicted to affect protein stability by destabilizing or truncating the folded core of APTX, catalytically inactive mutant
V263G
site-directed mutagenesis, a mutation causing the neurodegenerative disorder ataxia with oculomotor ataxia 1 (AOA1)
W279R
naturally occuring mutation, the mutant displays impaired AMP-lysine hydrolase activity, confers a late onset neurological disease AOA1
W279R
site-directed mutagenesis, a mutation causing the neurodegenerative disorder ataxia with oculomotor ataxia 1 (AOA1)
W279X
naturally occuring mutation causing Ataxia oculomotor apraxia type 1 (AOA1) autosomal recessive disease
W279X
naturally occuring mutation predicted to affect protein stability by destabilizing or truncating the folded core of APTX, catalytically inactive mutant, confers a late onset neurological disease AOA1
W279X
site-directed mutagenesis, a mutation causing the neurodegenerative disorder ataxia with oculomotor ataxia 1 (AOA1)
additional information
the biochemical and molecular abnormalities in APTX-depleted cells are recapitulated by knockdown of APE1 in Hela cells and are rescued by overexpression of NRF1/2. Importantly, pharmacological upregulation of NRF1 alone by 5-aminoimidazone-4-carboxamide ribonucleotide does not rescue the phenotype, which, in contrast, is reversed by the upregulation of NRF2 by rosiglitazone. The lack of aprataxin causes reduction of the pathway APE1/NRF1/NRF2 and their target genes. APTX-mutant fibroblasts show reduced succinate dehydrogenase. APTX-mutant fibroblasts show reduced levels and biosynthesis of CoQ10. Levels of APE1 are reduced in APTX-mutant and APTX-depleted cells. Phenotype, overview
additional information
construction of hnt3DELTA single mutants and HNT3 knockout mutants, including apn1DELTA/apn2DELTA/tpp1DELTA and ntg1DELTA/ntg2DELTA/ogg1DELTA. Loss of HNT3 in rad27DELTA cells, which are deficient in long-patch base excision repair (LP-BER), results in synergistic sensitivity to H2O2 and methylmethane sulfonate. HNT3 deletion partially rescues H2O2 sensitivity in recombination deficient rad51DELTA and rad52DELTA cells. Hnt3 point mutations and complementation with human aprataxin. Phenotypes, overview
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Hanaoka, K.; Tanaka, W.; Kayanuma, M.; Shoji, M.
A QM/MM study of the 5'-AMP DNA hydrolysis of aprataxin
Chem. Phys. Lett.
631-632
16-20
2015
Homo sapiens (Q7Z2E3)
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brenda
Horton, J.K.; Stefanick, D.F.; Caglayan, M.; Zhao, M.L.; Janoshazi, A.K.; Prasad, R.; Gassman, N.R.; Wilson, S.H.
XRCC1 phosphorylation affects aprataxin recruitment and DNA deadenylation activity
DNA Repair
64
26-33
2018
Saccharomyces cerevisiae (Q08702), Homo sapiens (Q7Z2E3)
brenda
Tumbale, P.; Schellenberg, M.; Mueller, G.; Fairweather, E.; Watson, M.; Little, J.; Krahn, J.; Waddell, I.; London, R.; Williams, R.
Mechanism of APTX nicked DNA sensing and pleiotropic inactivation in neurodegenerative disease
EMBO J.
37
e98875
2018
Homo sapiens (Q7Z2E3)
brenda
Garcia-Diaz, B.; Barca, E.; Balreira, A.; Lopez, L.C.; Tadesse, S.; Krishna, S.; Naini, A.; Mariotti, C.; Castellotti, B.; Quinzii, C.M.
Lack of aprataxin impairs mitochondrial functions via downregulation of the APE1/NRF1/NRF2 pathway
Hum. Mol. Genet.
24
4516-4529
2015
Homo sapiens (Q7Z2E3)
brenda
Schellenberg, M.J.; Tumbale, P.P.; Williams, R.S.
Molecular underpinnings of Aprataxin RNA/DNA deadenylase function and dysfunction in neurological disease
Prog. Biophys. Mol. Biol.
117
157-165
2015
Homo sapiens (Q7Z2E3)
brenda