Excision of uracil from DNA by the hyperthermophilic Afung protein is dependent on the opposite base and stimulated by heat-induced transition to a more open structure.
Hydrolytic deamination of DNA-cytosines into uracils is a major source of spontaneously induced mutations, and at elevated temperatures the rate of cytosine deamination is increased. Uracil lesions are repaired by the base excision repair pathway, which is initiated by a specific uracil DNA glycosylase enzyme (UDG). The hyperthermophilic archaeon Archaeoglobus fulgidus contains a recently characterized novel type of UDG (Afung), and in this paper we describe the over-expression of the afung gene and characterization of the encoded protein. Fluorescence and activity measurements following incubation at different temperatures may suggest the following model describing structure-activity relationships: At temperatures from 20 to 50 degrees C Afung exists as a compact protein exhibiting low enzyme activity, whereas at temperatures above 50 degrees C, the Afung conformation opens up, which is associated with the acquisition of high enzyme activity. The enzyme exhibits opposite base-dependent excision of uracil in the following order: U>U:T>U:C>>U:G>>U:A. Afung is product-inhibited by uracil and shows a pronounced inhibition by p-hydroxymercuribenzoate, indicating a cysteine residue essential for enzyme function. The Afung protein was estimated to be present in A. fulgidus at a concentration of approximately 1000 molecules per cell. Kinetic parameters determined for Afung suggest a significantly lower level of enzymatic uracil release in A. fulgidus as compared to the mesophilic Escherichia coli.
Knaevelsrud
I
I
School of Science and Technology, Stavanger University College, Ullandhaug, P.O. Box 2557, N-4091 Stavanger, Norway.
Ruoff
P
P
Anensen
H
H
Klungland
A
A
Bjelland
S
S
Birkeland
N K
NK
D000595:Amino Acid Sequence; D001105:Archaea / Q000201:enzymology; D019843:Archaeal Proteins / Q000235:genetics / Q000302:isolation & purification / Q000502:physiology*; D019611:Archaeoglobus fulgidus / Q000201:enzymology* / Q000235:genetics; D001419:Bacteria / Q000201:enzymology; D020029:Base Pairing; D002474:Cell-Free System; D003001:Cloning, Molecular; D004247:DNA / Q000378:metabolism*; D004249:DNA Damage; D045647:DNA Glycosylases; D004260:DNA Repair / Q000502:physiology*; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007700:Kinetics; D008969:Molecular Sequence Data; D009154:Mutation; D009699:N-Glycosyl Hydrolases / Q000235:genetics / Q000302:isolation & purification / Q000502:physiology*; D009690:Nucleic Acid Conformation; D010802:Phylogeny; D011487:Protein Conformation; D011489:Protein Denaturation; D011993:Recombinant Fusion Proteins / Q000302:isolation & purification / Q000502:physiology; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D014498:Uracil / Q000378:metabolism*; D051981:Uracil-DNA Glycosidase
D019843:Archaeal Proteins; D011993:Recombinant Fusion Proteins; D014498:Uracil; D004247:DNA; D045647:DNA Glycosylases; D009699:N-Glycosyl Hydrolases; D051981:Uracil-DNA Glycosidase