title: Active site of (A)BC excinuclease. I. Evidence for 5' incision by UvrC through a catalytic site involving Asp399, Asp438, Asp466, and His538 residues.
abstract: (A)BC excinuclease of Escherichia coli removes damaged nucleotides from DNA by hydrolyzing the 8th phosphodiester bond 5' and the 15th phosphodiester bond 3' to the modified base. The activity results from the ordered action of UvrA, UvrB, and UvrC proteins. The role of UvrA is to help assemble the UvrB.DNA complex, and it is not involved in the actual incision reactions which are carried out by UvrB and UvrC. To investigate the role of UvrC in the nuclease activity a subset of His, Asp, and Glu residues in the C-terminal half of the protein were mutagenized in vitro. The effect of these mutations on UV resistance in vivo and incision activity in vitro were investigated. Mutations, H538F, D399A, D438A, and D466A conferred extreme UV sensitivity. Enzyme reconstituted with these mutant proteins carried out normal 3' incision but was completely defective in 5' incision activity. Our data suggest that UvrC makes the 5' incision by employing a mechanism whereby the three carboxylates acting in concert with H538 and a Mg2+ ion facilitate nucleophilic attack by an active site water molecule.
authors.affiliation: Department of Biochemistry and Biophysics, University of North Carolina School of Medicine, Chapel Hill 27599.
authors.forename: J J
authors.initials: JJ
authors.lastname: Lin
authors.forename: A
authors.initials: A
authors.lastname: Sancar
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000595:Amino Acid Sequence; D001224:Aspartic Acid; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D004265:DNA Helicases; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004307:Dose-Response Relationship, Radiation; D004706:Endodeoxyribonucleases / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology* / Q000528:radiation effects; D029968:Escherichia coli Proteins; D005798:Genes, Bacterial; D006639:Histidine; D016297:Mutagenesis, Site-Directed; D014466:Ultraviolet Rays; D016335:Zinc Fingers / Q000502:physiology
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; C058093:UvrB protein, E coli; D001224:Aspartic Acid; D006639:Histidine; D004706:Endodeoxyribonucleases; C066567:UvrC protein, E coli; C036385:endodeoxyribonuclease uvrABC; C068631:UvrA protein, E coli; D000251:Adenosine Triphosphatases; D004265:DNA Helicases