NMR Structures of a Nonapeptide from DNA Binding Domain of Human Polymerase-α Determined by Iterative Complete-Relaxation-Matrix Approach

Abstract

Nuclear magnetic resonance structures of a nonapeptide, ERFKCPCPT, selected from the DNA binding domain of human polymerase-a, were determined by complete relaxation matrix analysis of transverse NOE data. The structures exhibit a type III turn with residues KCPC, and the remaining residues exhibit non-ordered structures. The turn was confirmed by α, N (i,i+3) connectivity, a low temperature coefficient of NH chemical shift (−3.1 × 1O⁻³) of the fourth residue, ³J_NHα coupling constants, and characteristic CD peaks at 228 and 200 nm. Furthermore, ø and ψ dihedral angles for the i + 1, and i + 2 residues of the tum are found to be−80 and−41 and−60 and−40 degrees. The first proline residue is trans- while the second exists in both eis- and trans- configurations, with trans- being more than 80% populated. The trans-configuration was established from C5α-P6α correlation and ø and ψ angles of the proline. The five-membered proline ring is in DOWN puckered (C-β-exo/C-γ-endo) conformation. The structure of the peptide reveals that the two cysteine thiols are−5 A° apart and appropriately positioned to covalently bind cis-diamminedichloroplatinum(II), a widely used anti-cancer drug.