title: Vitamin B6 biosynthesis by the malaria parasite Plasmodium falciparum: biochemical and structural insights.
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.
authors.affiliation: Abteilung für Parasitologie, Universitätsklinikum Heidelberg, Im Neuenheimer Feld 324, D-69120 Heidelberg, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Gengenbacher
authors.forename: Teresa B
authors.initials: TB
authors.lastname: Fitzpatrick
authors.forename: Thomas
authors.initials: T
authors.lastname: Raschle
authors.forename: Karlheinz
authors.initials: K
authors.lastname: Flicker
authors.forename: Irmgard
authors.initials: I
authors.lastname: Sinning
authors.forename: Sylke
authors.initials: S
authors.lastname: Müller
authors.forename: Peter
authors.initials: P
authors.lastname: Macheroux
authors.forename: Ivo
authors.initials: I
authors.lastname: Tews
authors.forename: Barbara
authors.initials: B
authors.lastname: Kappes
mesh_terms: D000818:Animals; D000953:Antigens, Protozoan / Q000737:chemistry; D001412:Bacillus subtilis / Q000378:metabolism; D015153:Blotting, Western; D002384:Catalysis; D020134:Catalytic Domain; D003001:Cloning, Molecular; D018360:Crystallography, X-Ray; D019992:Databases as Topic; D004591:Electrophoresis, Polyacrylamide Gel; D005816:Genetic Complementation Test; D005972:Glutaminase / Q000737:chemistry / Q000378:metabolism; D015151:Immunoblotting; D007477:Ions; D008288:Malaria / Q000469:parasitology*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009841:Oligonucleotides / Q000737:chemistry; D010963:Plasmodium falciparum / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D015800:Protozoan Proteins / Q000737:chemistry; D011994:Recombinant Proteins / Q000737:chemistry; D013997:Time Factors; D025101:Vitamin B 6 / Q000096:biosynthesis* / Q000737:chemistry
chemical_list: D000953:Antigens, Protozoan; D007477:Ions; D009841:Oligonucleotides; D015800:Protozoan Proteins; D011994:Recombinant Proteins; D025101:Vitamin B 6; D005972:Glutaminase