title: dNTP binding site in rat DNA polymerase beta revealed by controlled proteolysis and azido photoprobe cross-linking.
abstract: Mild proteolysis of rat DNA polymerase beta (beta-pol) generates an N-terminal 8 kDa domain and a C-terminal 31 kDa domain; the 31 kDa domain is degraded to 6 and 27 kDa fragments by further proteolysis [Kumar, A., Widen, S.G., Williams, K.R., Kedar, P., Karpel, R.L., & Wilson S.H. (1990) J. Biol. Chem. 265, 2124-2131]. In the present study, we found that more vigorous trypsin digestion of the 27 kDa fragment of beta-pol produces 10 and 12 kDa subdomains. Thus, rat beta-pol has four distinct proteolytic fragments of 8, 6, 10, and 12 kDa, extending from the N-terminus to the C-terminus, respectively. To map the location of the dNTP binding site(s), intact beta-pol was photoaffinity labeled with 8-azido-ATP or 5-azido-dUTP in presence or absence of competitor dNTP (dATP). The labeled enzyme was subjected to controlled proteolysis, and the resulting labeled peptides were separated and sequenced. Competition with dATP showed that three regions of beta-pol in solution combine to form the dNTP binding pocket as follows: residues 4-40 of the 8 kDa domain; residues 142-206 of the 10 kDa subdomain; and residues 263-280 of the 12 kDa subdomain (alpha-helices M and N). These results are discussed in light of the recent crystal structure of dATP bound to rat beta-pol.
authors.affiliation: Sealy Center for Molecular Science, University of Texas Medical Branch, Galveston, Texas 77555-1068, USA.
authors.forename: D K
authors.initials: DK
authors.lastname: Srivastava
authors.forename: R K
authors.initials: RK
authors.lastname: Evans
authors.forename: A
authors.initials: A
authors.lastname: Kumar
authors.forename: W A
authors.initials: WA
authors.lastname: Beard
authors.forename: S H
authors.initials: SH
authors.lastname: Wilson
mesh_terms: D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D000345:Affinity Labels / Q000378:metabolism / Q000494:pharmacology; D000595:Amino Acid Sequence; D000818:Animals; D001386:Azides / Q000378:metabolism / Q000494:pharmacology; D001665:Binding Sites; D003432:Cross-Linking Reagents / Q000378:metabolism / Q000494:pharmacology; D004256:DNA Polymerase I / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D003854:Deoxyribonucleotides / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D005091:Exons / Q000235:genetics; D008958:Models, Molecular; D015335:Molecular Probes / Q000378:metabolism; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D010782:Photolysis; D011487:Protein Conformation; D051381:Rats; D014544:Uridine Triphosphate / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology
chemical_list: D000345:Affinity Labels; D001386:Azides; D003432:Cross-Linking Reagents; D003854:Deoxyribonucleotides; D015335:Molecular Probes; D010446:Peptide Fragments; C072279:5-azidouridine-5'-triphosphate; C017040:8-azidoadenosine 5'-triphosphate; D000255:Adenosine Triphosphate; D004256:DNA Polymerase I; D014544:Uridine Triphosphate