Structural and catalytic insights into HoLaMa, a derivative of Klenow DNA polymerase lacking the proofreading domain
by Michael Kovermann, Alessandra Stefan, Anna Castaldo, Sara Caramia, Alejandro Hochkoeppler
We report here on the stability and catalytic properties of the HoLaMa DNA polymerase, a Klenow sub-fragment lacking the 3’-5’ exonuclease domain. HoLaMa was overexpressed in Escherichia coli, and the enzyme was purified by means of standard chromatographic techniques. High-resolution NMR experiments revealed that HoLaMa is properly folded at pH 8.0 and 20°C. In addition, urea induced a cooperative folding to unfolding transition of HoLaMa, possessing an overall thermodynamic stability and a transition midpoint featuring ΔG and CM equal to (15.7 ± 1.9) kJ/mol and (3.5 ± 0.6) M, respectively. When the catalytic performances of HoLaMa were compared to those featured by the Klenow enzyme, we did observe a 10-fold lower catalytic efficiency by the HoLaMa enzyme. Surprisingly, HoLaMa and Klenow DNA polymerases possess markedly different sensitivities in competitive inhibition assays performed to test the effect of single dNTPs.