Vitamin B6 biosynthesis by the malaria parasite Plasmodium falciparum: biochemical and structural insights |
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Authors: | Gengenbacher Martin Fitzpatrick Teresa B Raschle Thomas Flicker Karlheinz Sinning Irmgard Müller Sylke Macheroux Peter Tews Ivo Kappes Barbara |
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Institution: | Abteilung für Parasitologie, Universit?tsklinikum Heidelberg, Im Neuenheimer Feld 324, D-69120 Heidelberg, Germany. |
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Abstract: | Vitamin B6 is one of nature's most versatile cofactors. Most organisms synthesize vitamin B6 via a recently discovered pathway employing the proteins Pdx1 and Pdx2. Here we present an in-depth characterization of the respective orthologs from the malaria parasite, Plasmodium falciparum. Expression profiling of Pdx1 and -2 shows that blood-stage parasites indeed possess a functional vitamin B6 de novo biosynthesis. Recombinant Pdx1 and Pdx2 form a complex that functions as a glutamine amidotransferase with Pdx2 as the glutaminase and Pdx1 as pyridoxal-5 '-phosphate synthase domain. Complex formation is required for catalytic activity of either domain. Pdx1 forms a chimeric bi-enzyme with the bacterial YaaE, a Pdx2 ortholog, both in vivo and in vitro, although this chimera does not attain full catalytic activity, emphasizing that species-specific structural features govern the interaction between the protein partners of the PLP synthase complexes in different organisms. To gain insight into the activation mechanism of the parasite bi-enzyme complex, the three-dimensional structure of Pdx2 was determined at 1.62 A. The obstruction of the oxyanion hole indicates that Pdx2 is in a resting state and that activation occurs upon Pdx1-Pdx2 complex formation. |
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