Replication fork-stimulated eIF-4A from Plasmodium cynomolgi unwinds DNA in the 3' to 5' direction and is inhibited by DNA-interacting compounds

Abstract

Plasmodium cynomolgi DEAD-box DNA helicase 45 (PcDDH45) is an ATP-dependent DNA-unwinding enzyme with intrinsic DNA-dependent ATPase activity and is highly homologous to eIF-4A. In this study, we have further characterized and tested the effect of various DNA-interacting compounds on the DNA-unwinding activity of PcDDH45. The results show that PcDDH45 translocates in the 3' to 5' direction along the bound strand, a replication fork-like structure of the substrate stimulates its DNA-unwinding activity, and it failed to unwind blunt-ended duplex DNA. Of various compounds tested, only cisplatin, 4',6'-diamidino-2-phenylindole, daunorubicin, and nogalamycin were inhibitory to the unwinding activity of PcDDH45 with apparent IC₅₀ values of 1.0, 4.0, 7.5, and 1.7 μM, respectively. These results suggest that the interaction of these compounds with duplex DNA generate a complex that probably impedes the translocation of PcDDH45, resulting in inhibition of unwinding activity. This study is one of the first to demonstrate the effect of various DNA-binding compounds on a malaria parasite DNA helicase and should make an important contribution to our better understanding of the nucleic acid transactions in the parasite.