title: Probing the Flexibility of the Catalytic Nucleophile in the Lyase Catalytic Pocket of Human DNA Polymerase β with Unnatural Lysine Analogues.
abstract: DNA polymerase β (Pol β) is a key enzyme in mammalian base excision repair (BER), contributing stepwise 5'-deoxyribose phosphate (dRP) lyase and "gap-filling" DNA polymerase activities. The lyase reaction is believed to occur via a β-elimination reaction following the formation of a Schiff base between the dRP group at the pre-incised apurinic/apyrimidinic site and the ε-amino group of Lys72. To probe the steric constraints on the formation and subsequent resolution of the putative Schiff base intermediate within the lyase catalytic pocket, Lys72 was replaced with each of several nonproteinogenic lysine analogues. The modified Pol β enzymes were produced by coupled in vitro transcription and translation from a modified DNA template containing a TAG codon at the position corresponding to Lys72. In the presence of a misacylated tRNACUAtranscript, suppression of the UAG codon in the transcribed mRNA led to elaboration of full length Pol β having a lysine analogue at position 72. Replacement of the primary nucleophilic amine with a secondary amine in the form of N-methyllysine (4) affected mainly the stability of the Schiff base intermediate and resulted in relatively moderate inhibition of lyase activity and BER. Elongation of the side chain of the catalytic residue by one methylene group, achieved by introduction of homolysine (6) at position 72, apparently shifted the amino group to a position less favorable for Schiff base formation. Interestingly, this effect was attenuated when the side chain was elongated by replacing one side-chain methylene group with a bridging S atom (thialysine, 2). In comparison, replacement of lysine 72 with an analogue having a guanidine moiety in lieu of an ε-amino group (homoarginine, 5) or a sterically constrained secondary amine (piperidinylalanine, 3) led to almost complete suppression of dRP excision activity and the ability of Pol β to support BER. These results help to define the tolerance of Pol β to subtle local structural and functional alterations.
authors.affiliation: Biodesign Center for BioEnergetics and School of Molecular Sciences, Arizona State University , Tempe, Arizona 85287, United States.
authors.forename: Sasha M
authors.initials: SM
authors.lastname: Daskalova
authors.affiliation: Biodesign Center for BioEnergetics and School of Molecular Sciences, Arizona State University , Tempe, Arizona 85287, United States.
authors.forename: Chandrabali
authors.initials: C
authors.lastname: Bhattacharya
authors.affiliation: Biodesign Center for BioEnergetics and School of Molecular Sciences, Arizona State University , Tempe, Arizona 85287, United States.
authors.forename: Larisa M
authors.initials: LM
authors.lastname: Dedkova
authors.affiliation: Biodesign Center for BioEnergetics and School of Molecular Sciences, Arizona State University , Tempe, Arizona 85287, United States.
authors.forename: Sidney M
authors.identifier: 0000-0002-5429-2462
authors.initials: SM
authors.lastname: Hecht
mesh_terms: D000595:Amino Acid Sequence; D020134:Catalytic Domain; D003001:Cloning, Molecular; D003062:Codon / Q000235:genetics / Q000378:metabolism; D004247:DNA / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D019951:DNA Polymerase beta / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D004260:DNA Repair; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008239:Lysine / Q000031:analogs & derivatives* / Q000378:metabolism; D008958:Models, Molecular; D019761:Phosphorus-Oxygen Lyases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D014176:Protein Biosynthesis; D000072417:Protein Domains; D017433:Protein Structure, Secondary; D012357:RNA, Transfer, Lys / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012545:Schiff Bases / Q000737:chemistry / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: D003062:Codon; D012357:RNA, Transfer, Lys; D011994:Recombinant Proteins; D012545:Schiff Bases; D004247:DNA; C423906:5'-deoxyribose phosphate lyase; D019951:DNA Polymerase beta; D019761:Phosphorus-Oxygen Lyases; D008239:Lysine