Structural insights on the pamoic acid and the 8 kDa domain of DNA polymerase beta complex: towards the design of higher-affinity inhibitors.
BACKGROUND
DNA polymerase beta (pol beta), the error-prone DNA polymerase of single-stranded DNA break repair as well as base excision repair pathways, is overexpressed in several tumors and takes part in chemotherapeutic agent resistance, like that of cisplatin, through translesion synthesis. For this reason pol beta has become a therapeutic target. Several inhibitors have been identified, but none of them presents a sufficient affinity and specificity to become a drug. The fragment-based inhibitor design allows an important improvement in affinity of small molecules. The initial and critical step for setting up the fragment-based strategy consists in the identification and structural characterization of the first fragment bound to the target.


RESULTS
We have performed docking studies of pamoic acid, a 9 micromolar pol beta inhibitor, and found that it binds in a single pocket at the surface of the 8 kDa domain of pol beta. However, docking studies provided five possible conformations for pamoic acid in this site. NMR experiments were performed on the complex to select a single conformation among the five retained. Chemical Shift Mapping data confirmed pamoic acid binding site found by docking while NOESY and saturation transfer experiments provided distances between pairs of protons from the pamoic acid and those of the 8 kDa domain that allowed the identification of the correct conformation.


CONCLUSIONS
Combining NMR experiments on the complex with docking results allowed us to build a three-dimensional structural model. This model serves as the starting point for further structural studies aimed at improving the affinity of pamoic acid for binding to DNA polymerase beta.
Hazan
Corinne
C
University of Toulouse, UPS; IPBS (Institute of Pharmacology and Structural Biology), 205 route de Narbonne, 31077 Toulouse, France. corinne.hazan@ipbs.fr
Boudsocq
François
F
Gervais
Virginie
V
Saurel
Olivier
O
Ciais
Marion
M
Cazaux
Christophe
C
Czaplicki
Jerzy
J
Milon
Alain
A
D001665:Binding Sites; D019951:DNA Polymerase beta / Q000037:antagonists & inhibitors* / Q000737:chemistry* / Q000378:metabolism; D004277:DNA, Single-Stranded / Q000378:metabolism; D015195:Drug Design; D004791:Enzyme Inhibitors / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology*; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D009284:Naphthols / Q000737:chemistry* / Q000378:metabolism* / Q000494:pharmacology; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011522:Protons
D004277:DNA, Single-Stranded; D004791:Enzyme Inhibitors; D009284:Naphthols; D010446:Peptide Fragments; D011522:Protons; C004368:pamoic acid; D019951:DNA Polymerase beta