9ics
DNA POLYMERASE BETA (E.C.2.7.7.7)/DNA COMPLEX + 2',3'-DIDEOXYCYTIDINE-5'-TRIPHOSPHATE, SOAKED IN THE PRESENCE OF DDCTP AND MNCL2
|
OverviewOverview
When crystals of human DNA polymerase beta (pol beta) complexed with DNA, [Pelletier, H., Sawaya, M. R., Wolfle, W., Wilson, S. H., & Kraut, J., (1996) Biochemistry 35, 12742-12761] are soaked in the presence of dATP, and Mn2+, X-ray structural analysis shows that nucleotidyl transfer to the, primer 3'-OH takes place directly in the crystals, even though the DNA is, blunt-ended at the active site. Under similar crystal-soaking conditions, there is no evidence for a reaction when Mn2+ is replaced by Mg2+, which, is thought to be the divalent metal ion utilized by most polymerases in, vivo. These results suggest that one way Mn2+ may manifest its mutagenic, effect on polymerases is by promoting greater reactivity than Mg2+ at the, catalytic site, thereby allowing the nucleotidyl transfer reaction to take, place with little or no regard to instructions from a template., Non-template-directed nucleotidyl transfer is also observed when pol, beta-DNA cocrystals are soaked in the presence of dATP and Zn2+, but the, reaction products differ in that the sugar moiety of the incorporated, nucleotide appears distorted or otherwise cleaved, in agreement with, reports that Zn2+ may act as a polymerase inhibitor rather than as a, mutagen [Sirover, M. A., & Loeb, L. A. (1976) Science 194, 1434-1436]., Although no reaction is observed when crystals are soaked in the presence, of dATP and other metal ions such as Ca2+, Co2+, Cr3+, or Ni2+, X-ray, structural analyses show that these metal ions coordinate the triphosphate, moiety of the nucleotide in a manner that differs from that observed with, Mg2+. In addition, all metal ions tested, with the exception of Mg2+, promote a change in the side-chain position of aspartic acid 192, which is, one of three highly conserved active-site carboxylate residues. Soaking, experiments with nucleotides other than dATP (namely, dCTP, dGTP, dTTP, ATP, ddATP, ddCTP, AZT-TP, and dATP alpha S) reveal a non-base-specific, binding site on pol beta for the triphosphate and sugar moieties of a, nucleotide, suggesting a possible mechanism for nucleotide selectivity, whereby triphosphate-sugar binding precedes a check for correct base, pairing with the template.
About this StructureAbout this Structure
9ICS is a Single protein structure of sequence from Homo sapiens with MN, NA and DCT as ligands. Full crystallographic information is available from OCA.
ReferenceReference
A structural basis for metal ion mutagenicity and nucleotide selectivity in human DNA polymerase beta., Pelletier H, Sawaya MR, Wolfle W, Wilson SH, Kraut J, Biochemistry. 1996 Oct 1;35(39):12762-77. PMID:8841119
Page seeded by OCA on Mon Nov 12 23:57:07 2007