Modifying the beta,gamma leaving-group bridging oxygen alters nucleotide incorporation efficiency, fidelity, and the catalytic mechanism of DNA polymerase beta.
DNA polymerase catalysis and fidelity studies typically compare incorporation of "right" versus "wrong" nucleotide bases where the leaving group is pyrophosphate. Here we use dGTP analogues replacing the beta,gamma-bridging O with CH2, CHF, CF2, or CCl2 to explore leaving-group effects on the nucleotidyl transfer mechanism and fidelity of DNA polymerase (pol) beta. T.G mismatches occur with fidelities similar to dGTP with the exception of the CH2 analogue, which is incorporated with 5-fold higher fidelity. All analogues are observed to bind opposite template C with Kds between 1 and 4 microM, and structural evidence suggests that the analogues bind in essentially the native conformation, making them suitable substrates for probing linear free energy relationships (LFERs) in transient-kinetics experiments. Importantly, Brnsted correlations of log(kpol) versus leaving-group pKa for both right and wrong base incorporation reveal similar sensitivities (betalg approximately -0.8) followed by departures from linearity, suggesting that a chemical step rather than enzyme conformational change is rate-limiting for either process. The location of the breaks relative to pKas of CF2, O, and the sterically bulky CCl2-bridging compounds suggests a modification-induced change in the mechanism by stabilization of leaving-group elimination. The results are addressed theoretically in terms of the energetics of successive primer 3'-O addition (bond forming) and pyrophosphate analogue elimination (bond breaking) reaction energy barriers.
Sucato
Christopher A
CA
Department of Chemistry, University of Southern California, Los Angeles, California 90089, USA.
Upton
Thomas G
TG
Kashemirov
Boris A
BA
Batra
Vinod K
VK
Martínek
Václav
V
Xiang
Yun
Y
Beard
William A
WA
Pedersen
Lars C
LC
Wilson
Samuel H
SH
McKenna
Charles E
CE
Florián
Jan
J
Warshel
Arieh
A
Goodman
Myron F
MF
D001483:Base Sequence; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D004247:DNA / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics; D019951:DNA Polymerase beta / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D003848:Deoxyguanine Nucleotides / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D009711:Nucleotides / Q000737:chemistry / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013379:Substrate Specificity; D013816:Thermodynamics
D003848:Deoxyguanine Nucleotides; D009711:Nucleotides; D011994:Recombinant Proteins; C029603:deoxyguanosine triphosphate; D004247:DNA; D019951:DNA Polymerase beta; D010100:Oxygen