Pyridoxal kinase knockout of Dictyostelium complemented by the human homologue

Pyridoxal kinase gene deletion leads to impaired growth, deranged redox metabolism and cell cycle arrest in Leishmania donovani

Pyridoxal kinase (PdxK) is a vitamin B6 salvage pathway enzyme which produces pyridoxal phosphate. We have investigated the impact of PdxK deletion in Leishmania donovani on parasite survivability, infectivity and cellular metabolism. LdPdxK mutants were generated by gene replacement strategy. All mutants showed significant reduction in growth in comparison to wild type. For PdxK mediated biochemical perturbations, only heterozygous mutants and complementation mutants were used as the growth of null mutants were compromised. Heterozygous mutant showed reduction invitro infectivity and higher cytosolic and mitochondrial ROS levels. Glutathione levels decreased significantly in heterozygous mutant indicating its involvement in cellular oxidative metabolism. Pyridoxal kinase gene deletion resulted in reduced ATP levels in parasites and arrest at G0/G1 phase of cell cycle. All these perturbations were rescued by PdxK gene complementation. This is the first report to confirm that LdPdxK plays an indispensable role in cell survival, pathogenicity, redox metabolism and cell cycle progression of L. donovani parasites. These results provide substantial evidence supporting PdxK as a therapeutic target for the development of specific antileishmanial drug candidates.

Expression analysis of a novel pyridoxal kinase messenger RNA splice variant, PKL, in oil rape suffering abiotic stress and phytohormones

Pyridoxal kinase is key enzyme for the biosynthesis of pyridoxal 5'-phosphate, the biologically active form of vitamin B6, in the salvage pathway. A pyridoxal kinase gene, BnPKL (GenBank accession No. DQ463962), was isolated from oilseed rape (Brassica napus L.) following water stress through rapid amplification of complementary DNA (cDNA) ends. The results showed that the gene had two splice variants: PKL and PKL2. PKL, the long cDNA, encodes a 334 amino acid protein with a complete ATP-binding site, pyridoxal kinase-binding site and dimer interface site of a pyridoxal kinase, while PKL2, the short cDNA, lacked a partial domain. Southern blot showed that there were two copies in Brassica napus. The expression of BnPKL cDNA could rescue the mutant phenotype of Escherichia coli defective in pyridoxal kinase. Real-time reverse transcription-polymerase chain reaction revealed that the relative abundance of two transcripts are modulated by development and environmental stresses. Abscisic acid and NaCl were inclined to decrease PKL expression, but H2O2 and cold temperatures induced the PKL expression. In addition, the PKL expression could be transiently induced by jasmonate acid at an early stage, abscisic acid, salicylic acid and jasmonate acid enhanced the PKL expression in roots. Our results demonstrated that BnPKL was a pyridoxal kinase involved in responses to biotic and abiotic stresses.

Bombyx mori Pyridoxal Kinase cDNA Cloning and Enzymatic Characterization

Pyridoxal kinase (PLK) (EC 2.7.1.35) catalyzes the ATP-dependent phosphorylation of pyridoxal, generating pyridoxal-5.-phosphate (PLP), an important cofactor for many enzymatic reactions. Bombyx mori, similar to mammals, relies on a nutritional source of vitamin B6 to synthesize PLP. This article describes how a cDNA encoding PLK was cloned from Bombyx mori using the PCR method (GenBank accession number: DQ452397). The cDNA has an 894 bp open reading frame and encodes a protein of 298 amino acid residues with a molecular mass of 33.1 kDa. The amino acid sequence shares 48.6% identity with that of human PLK, and it also contains signature conserved motifs of the PLK family. However, the protein is 10 or more amino acids shorter than the PLK from mammals and plants, and several amino acid residues conserved in the PLK from mammals and plants are changed in the protein. The cDNA cloned was expressed successfully in Escherichia coli using the T7 promoter/T7 RNA polymerase expression system, and the crude extracts containing the expressed product were found to have strong PLK enzymatic activity with a value of 30 nmol/min/mg, confirming that the cDNA encodes the functional PLK of Bombyx mori. This is the first identification of a gene encoding PLK in insects.

The pyridoxal kinase gene TaPdxK from wheat complements vitamin B6 synthesis-defective Escherichia coli

Pyridoxal kinase (EC 2.7.1.35) is a key enzyme in the conversion of vitamin B6 to pyridoxal 5'-phosphate (PLP). PLP is the crucial cofactor required by numerous enzymes involved in amino acids metabolism. Recently, studies with Arabidopsis salt overly sensitive 4 mutants demonstrated that pyridoxal kinase is a novel salt tolerance determinant important for the regulation of Na+ and K+ homeostasis in plants. We describe here the TaPdxK gene which encodes a pyridoxal kinase, cloned from Triticum aestivum by RACE PCR method. The putative amino acid sequence of TaPdxK is 78% identical to Arabidopsis AtSOS4. Southern analysis suggests that there are at least two copies of pyridoxal kinase genes in wheat genome. The expression of TaPdxK cDNAs complements an Escherichia coli mutant defective in pyridoxal kinase. TaPdxK transcripts were detected in roots, shoots, spikes and anthers by RT-PCR analysis. TaPdxK expression level was not regulated by salt, ABA, and osmotic stress.