gms | German Medical Science

Hypusination in eukaryotic initiation factor 5A (EIF5A) is a unique posttranslational modification which so far has only been discovered in this protein. Hypusine was first isolated by Shiba et al. (1971) from brain cells and identified as a 4-amino-2-hydroxybutyl)lysine-derivative. This posttranslational modification is formed within two consecutive enzymatic steps i.e. deoxyhypusine synthase (DHS) and deoxyhypusine hydroxylase. Deoxyhypusine synthase transfers the aminobutyl moiety from the triamine spermidine to a specific lysine residue in EIF-5A while deoxyhypusine hydroxylase catalyzes hydroxylation in the side chain.

Over recent years we have identified both enzymes in the human malaria parasites P. falciparum and P. vivax. Both enzymes were evaluated as druggable targets [1]. Currently, investigations on the biological function of this unique posttranslational modification are performed. In recent experiments we showed that downregulation by silencing eiF-5A, dhs and dohh genes with shorthairpin RNAs leads to an impaired hypusine biosynthesis and to growth retardation of the parasite. Infection of NMRI mice with schizonts from the lethal P. berghei ANKA wildtype strain transgenic for plasmodial eIF-5A-specific shRNA or DHS-specific shRNA resulted in low parasitemia 2–9 days post infection before animals succumbed to hyperparasitemia similar to infections with the related but non-lethal phenotype P. berghei strain NK65. RT-PCR and Western blot experiments performed with blood from the transfected erythrocytic stages showed that both genes are important for the proliferation of the parasite. Moreover, these experiments clearly demonstrate that the hypusine pathway in Plasmodium is linked to human iNos induction .

Preliminary results of an in vivo knockdown show that eif-5A and dhs genes are essential for the proliferation of the parasite thus revisiting an old acquaintance for their importance in cell proliferation. This findings were even more supported in phenotyping experiments. To exclude any resistance association with the gene locus of eif-5A and dhs genes “knock in” experiments will be performed.