3sq8
From Proteopedia
Crystal Structure Analysis of the Yeast Tyrosyl-DNA Phosphodiesterase 1 H432R Mutant (SCAN1 Mutant)
Structural highlights
Function[TYDP1_YEAST] DNA repair enzyme that can remove a variety of covalent adducts from DNA through hydrolysis of a 3'-phosphodiester bond, giving rise to DNA with a free 3' phosphate. Catalyzes the hydrolysis of dead-end complexes between DNA and the topoisomerase I active site tyrosine residue. Hydrolyzes 3'-phosphoglycolates on protruding 3' ends on DNA double-strand breaks due to DNA damage by radiation and free radicals. Cleaves also 5' phosphotyrosyl adducts resulting from dead-end complexes between DNA and the active site tyrosine of topoisomerase II. Contributes to DNA repair after radiation damage. Acts on blunt-ended double-strand DNA breaks and on single-stranded DNA. May have low 3'exonuclease activity and may be able to remove a single nucleoside from the 3'end of DNA and RNA molecules with 3'hydroxyl groups. Has no exonuclease activity towards DNA or RNA with a 3'phosphate (By similarity).[1] [2] Publication Abstract from PubMedTyrosyl-DNA phosphodiesterase I (Tdp1) is a member of the phospholipase D superfamily that hydrolyzes 3'-phospho-DNA adducts via two conserved catalytic histidines-one acting as the lead nucleophile and the second acting as a general acid/base. Substitution of the second histidine specifically to arginine contributes to the neurodegenerative disease spinocerebellar ataxia with axonal neuropathy (SCAN1). We investigated the catalytic role of this histidine in the yeast protein (His432) using a combination of X-ray crystallography, biochemistry, yeast genetics, and theoretical chemistry. The structures of wild-type Tdp1 and His432Arg both show a phosphorylated form of the nucleophilic histidine that is not observed in the structure of His432Asn. The phosphohistidine is stabilized in the His432Arg structure by the guanidinium group that also restricts the access of nucleophilic water molecule to the Tdp1-DNA intermediate. Biochemical analyses confirm that His432Arg forms an observable and unique Tdp1-DNA adduct during catalysis. Substitution of His432 by Lys does not affect catalytic activity or yeast phenotype, but substitutions with Asn, Gln, Leu, Ala, Ser, and Thr all result in severely compromised enzymes and DNA topoisomerase I-camptothecin dependent lethality. Surprisingly, His432Asn did not show a stable covalent Tdp1-DNA intermediate that suggests another catalytic defect. Theoretical calculations revealed that the defect resides in the nucleophilic histidine and that the pK(a) of this histidine is crucially dependent on the second histidine and on the incoming phosphate of the substrate. This represents a unique example of substrate-activated catalysis that applies to the entire phospholipase D superfamily. Analysis of the Active-Site Mechanism of Tyrosyl-DNA Phosphodiesterase I: A Member of the Phospholipase D Superfamily.,Gajewski S, Comeaux EQ, Jafari N, Bharatham N, Bashford D, White SW, van Waardenburg RC J Mol Biol. 2011 Dec 6. PMID:22155078[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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