Structural basis of DNA ligase proofreading by aprataxin with insights into AOA1 neurodegenerative disease

Tuesday, October 25, 2011 — Poster Session II
Noon – 2:00 p.m.	Natcher Conference Center	NIEHS	STRUCTBIO-9

* FARE Award Winner

Authors

• P Tumbale
• D Appel
• R Kraehenbuehl
• PD Robertson
• J Williams
• J Krahn
• I Ahel
• RS William

Abstract

DNA ligases finalize DNA replication and repair through imperfect DNA nick-sealing reactions that when aborted, generate cytotoxic 5'-adenylation DNA damage which is repaired through enigmatic mechanisms by the Ataxia Oculomotor Apraxia 1 (AOA1) mutated gene product aprataxin (APTX). We report the X-ray crystal structure an APTX/DNA/AMP ternary complex, revealing composite active site and DNA interaction clefts formed via fusion of a HIT (histidine triad) nucleotide hydrolase with an unprecedented DNA minor groove binding C2HE Zn-finger (Znf). APTX employs a helical wedge to interrogate the base stack for DNA end/nick sensing. To access DNA 5'-adenylate for catalysis, HIT-Znf structure-specific DNA binding, the wedge, and an "FPK"-pivot together distort terminal DNA base-pairing, and rotate 5'-adenylate perpendicular to the duplex axis, into the active site pocket. Structures and mutagenesis support a HIT-Znf direct damage reversal repair mechanism, and illuminate protein folding, active site distortion, and FPK-pivot mutations underlying APTX dysfunction in neurodegenerative disease.

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