Investigation of the stability of D5SIC-DNAM-incorporated DNA duplex in Taq polymerase binary system: a systematic classical MD approach.

DNA polymerases are fundamental enzymes that play a crucial role in processing DNA with high fidelity and accuracy ensuring the faithful transmission of genetic information. The recognition of unnatural base pairs (UBPs) by polymerases, enabling their replication, represents a significant and groundbreaking discovery with profound implications for genetic expansion. Romesberg et al. examined the impact of DNA containing 2,6-dimethyl-2 H -isoquiniline-1-thione: D5SIC (DS) and 2-methoxy-3-methylnaphthalene: DNAM (DN) UBPs bound to T. aquaticus DNA polymerase ( Taq ) through crystal structure analysis. Here, we have used polarizable and nonpolarizable classical molecular dynamics (MD) simulations to investigate the structural aspects and stability of Taq in complex with a DNA duplex including a DS-DN pair in the terminal 3' and 5' positions. Our results suggest that the flexibility of UBP-incorporated DNA in the terminal position is arrested by the polymerase, thus preventing fraying and mispairing. Our investigation also reveals that the UBP remains in an intercalated conformation inside the active site, exhibiting two distinct orientations in agreement with experimental findings. Our analysis pinpoints particular residues responsible for favorable interactions with the UBP, with some relying on van der Waals interactions while other on Coulombic forces.