RESUMO
Adenylate kinases (AK; ATP+AMP<-->2 ADP; E.C. 2.7.4.3.) are enzymes essentially involved in energy metabolism and macromolecular biosynthesis. As we reported previously, the malarial parasite Plasmodium falciparum possesses one genuine AK and one GTP-AMP phosphotransferase. Analysis of the P. falciparum genome suggested the presence of one additional adenylate kinase, which we designated AK2. Recombinantly produced AK2 was found to be a monomeric protein of 33 kDa showing a specific activity of 10 U/mg with ATP and AMP as a substrate pair and to interact with the AK-specific inhibitor P(1),P(5)-(diadenosine-5')-pentaphosphate (IC(50)=200 nM). At its N-terminus AK2 carries a predicted myristoylation sequence. This sequence is only present in AK2 of P. falciparum causing the severe tropical malaria and not in other malarial parasites. We heterologously coexpressed AK2 and P. falciparum N-myristoyltransferase (NMT) in the presence of myristate in Escherichia coli. As demonstrated by protein purification and mass spectrometry, AK2 is indeed myristoylated under catalysis of the parasites' transferase. The modification significantly enhances the stability of the kinase. Furthermore, AK2 and NMT were shown to interact strongly with each other forming a heterodimeric protein in vitro. To our knowledge this is the first direct evidence that P. falciparum NMT myristoylates an intact malarial protein.