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PDBsum entry 1n3c
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Hydrolase, lyase/DNA
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PDB id
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1n3c
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Contents |
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* Residue conservation analysis
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References listed in PDB file
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Key reference
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Title
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Structural and biochemical exploration of a critical amino acid in human 8-Oxoguanine glycosylase.
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Authors
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D.P.Norman,
S.J.Chung,
G.L.Verdine.
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Ref.
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Biochemistry, 2003,
42,
1564-1572.
[DOI no: ]
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PubMed id
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Abstract
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Members of the HhH-GPD superfamily of DNA glycosylases are responsible for the
recognition and removal of damaged nucleobases from DNA. The hallmark of these
proteins is a motif comprising a helix-hairpin-helix followed by a Gly/Pro-rich
loop and terminating in an invariant, catalytically essential aspartic acid
residue. In this study, we have probed the role of this Asp in human
8-oxoguanine DNA glycosylase (hOgg1) by mutating it to Asn (D268N), Glu (D268E),
and Gln (D268Q). We show that this aspartate plays a dual role, acting both as
an N-terminal alpha-helix cap and as a critical residue for catalysis of both
base excision and DNA strand cleavage by hOgg1. Mutation of this residue to
asparagine, another helix-capping residue, preserves stability of the protein
while drastically reducing enzymatic activity. A crystal structure of this
mutant is the first to reveal the active site nucleophile Lys249 in the presence
of lesion-containing DNA; this structure offers a tantalizing suggestion that
base excision may occur by cleavage of the glycosidic bond and then attachment
of Lys249. Mutation of the aspartic acid to glutamine and glutamic acid
destabilizes the protein fold to a significant extent but, surprisingly,
preserves catalytic activity. Crystal structures of these mutants complexed with
an unreactive abasic site in DNA reveal these residues to adopt a sterically
disfavored helix-capping conformation.
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