5kt5 | pdb_00005kt5
Teranry complex of human DNA polymerase iota R96G inserting dCMPNPP opposite template G in the presence of Mn2+
Structural highlights
Function[POLI_HUMAN] Error-prone DNA polymerase specifically involved in DNA repair. Plays an important role in translesion synthesis, where the normal high-fidelity DNA polymerases cannot proceed and DNA synthesis stalls. Favors Hoogsteen base-pairing in the active site. Inserts the correct base with high-fidelity opposite an adenosine template. Exhibits low fidelity and efficiency opposite a thymidine template, where it will preferentially insert guanosine. May play a role in hypermutation of immunogobulin genes. Forms a Schiff base with 5'-deoxyribose phosphate at abasic sites, but may not have lyase activity.[1] [2] [3] [4] [5] [6] [7] Publication Abstract from PubMedDNA polymerase (pol) iota is a Y-family polymerase involved in translesion synthesis, exhibiting higher catalytic activity with Mn2+ than Mg2+. The human germline R96G variant impairs both Mn2+- and Mg2+-dependent activities of pol iota, while the Delta1-25 variant selectively enhances its Mg2+-dependent activity. We analyzed pre-steady-state kinetic and structural effects of these two metal ions and genetic variations on pol iota using pol iota core (residues 1-445) proteins. The presence of Mn2+ (0.15 mM) instead of Mg2+ (2 mM) caused a 770-fold increase in efficiency (kpol/Kd,dCTP) of pol iota for dCTP insertion opposite G, mainly due to a 450-fold decrease in Kd,dCTP. The R96G and Delta1-25 variants displayed a 53-fold decrease and a 3-fold increase, respectively, in kpol/Kd,dCTP for dCTP insertion opposite G with Mg2+ when compared to wild-type, substantially attenuated by substitution with Mn2+. Crystal structures of pol iota ternary complexes, including the primer terminus 3'-OH and a non-hydrolyzable dCTP analog opposite G with the active-site Mg2+ or Mn2+, revealed that Mn2+ achieves more optimal octahedral coordination geometry than Mg2+, with lower values in average coordination distance geometry in the catalytic metal A-site. Crystal structures of R96G revealed the loss of three H-bonds of residues Gly-96 and Tyr-93 with an incoming dNTP, due to the lack of an arginine as well as a destabilized Tyr-93 side chain secondary to the loss of a cation-pi interaction between both side chains. These results provide a mechanistic basis for alteration in pol iota catalytic function with coordinating metals and genetic variation. Kinetic and Structural Impact of Metal Ions and Genetic Variations on Human DNA Polymerase iota.,Choi JY, Patra A, Yeom M, Lee YS, Zhang Q, Egli M, Guengerich FP J Biol Chem. 2016 Aug 23. pii: jbc.M116.748285. PMID:27555320[8] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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