Modification of eukaryotic initiation factor 5A from Plasmodium vivax by a truncated deoxyhypusine synthase from Plasmodium falciparum: An enzyme with dual enzymatic properties

The increasing resistance of the malaria parasites enforces alternative directions in finding new drug targets. Present findings from the malaria parasite Plasmodium vivax, causing tertiary malaria, suggest eukaryotic initiation factor 5A (eIF-5A) to be a promising target for the treatment of malaria. Previously we presented the 162 amino acid sequence of eukaryotic initiation factor 5A (eIF-5A) from Plasmodium vivax. In the present study, we have expressed and purified the 20 kDa protein performed by one-step Nickel chelate chromatography. In Western blot experiments eIF-5A from P. vivax crossreacts with a polyclonal anti-eIF-5A antiserum from the plant Nicotiana plumbaginifolia (Solanaceae). Transcription of eIF-5A can be observed in both different developmental stages of the parasite being prominent in trophozoites. We recently published the nucleic acid sequence from a genomic clone of P. falciparum strain NF54 encoding a putative deoxyhypusine synthase (DHS), an enzyme that catalyzes the post-translational modification of eIF-5A. After removal of 22 amino acids DHS was expressed as a Histidin fusion protein and purified by Nickel affinity chromatography. Truncated DHS from P. falciparum modifies eIF-5A from P. vivax. DHS from P. falciparum NF54 is a bi-functional protein with dual enzymatic specificities, that is, DHS activity and homospermidine synthase activity (HSS) (0.047 pkatal/mg protein) like in other eukaryotes. Inhibition of DHS from P. falciparum resulted in a Ki of 0.1 μM for the inhibitor GC7 being 2000-fold less than the nonguanylated derivative 1,7-diaminoheptane. Dhs transcription occurs in both develomental stages suggesting its necessity in cell proliferation.

In the first step of hypusine biosynthesis deoxyhypusine synthase (DHS) catalyzes the transfer of the 4-aminobutyl moiety of spermidine to the ε-amino group of one specific lysine residue in eIF-5A to form deoxyhypusine. In the second step this intermediate is subsequently hydroxylated by deoxyhypusine hydroxylase (DHH or DOHH) to complete hypusine biosynthesis and thus eIF-5A maturation. CNI-1493 (former semapimod) and N-guanyl-1,7-diaminoheptane (GC7) are specific DHS inhibitors.Figure optionsDownload as PowerPoint slide