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Sterol uptake induced by an impairment of pyridoxal phosphate synthesis in Saccharomyces cerevisiae: cloning and sequencing of the PDX3 gene encoding pyridoxine (pyridoxamine) phosphate oxidase.

ABSTRACT: Exogenous sterols do not permeate wild-type Saccharomyces cerevisiae in aerobic conditions. However, mutant strain FKerg7, affected in lanosterol synthase, is a sterol auxotroph which is able to grow aerobically in the presence of ergosterol. Viability of this strain depends on the presence of an additional mutation, aux30, that leads to sterol permeability. Cells bearing the aux30 mutation fail to grow in standard yeast nitrogen base medium containing pyridoxine but grow normally if pyridoxine is replaced by either pyridoxal or pyridoxamine. These mutants are characterized by a lack in pyridoxine (pyridoxamine) phosphate oxidase [P(N/M)P oxidase] (EC 1.4.3.5) activity. The pleiotropic phenotype induced by the aux30 mutation includes a strong perturbation in amino acid biosynthesis. Strains bearing the aux30 mutation also display atypic fatty acid, sterol, and cytochrome patterns. Transformation of an aux30 strain with a replicative vector carrying the wild-type PDX3 gene encoding P(N/M)P oxidase restored wild-type fatty acid, sterol, and cytochrome patterns and suppressed exogenous sterol accumulation. It is proposed that sterol permeation of aux30 strains in mainly the consequence of their leaky Hem- character. The amino acid sequence of S. cerevisiae P(N/M)P oxidase inferred from the nucleotide sequence of PDX3 shows a high percentage of homology with the corresponding enzymes from Escherichia coli and Myxococcus xanthus. Several putative Gcn4p binding sequences are present in the PDX3 promoter region, leading to the assumption that transcription of this gene is under the general control of nitrogen metabolism.

SUBMITTER: Loubbardi A

PROVIDER: S-EPMC176811 | biostudies-other | 1995 Apr

REPOSITORIES: biostudies-other

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Sterol uptake induced by an impairment of pyridoxal phosphate synthesis in Saccharomyces cerevisiae: cloning and sequencing of the PDX3 gene encoding pyridoxine (pyridoxamine) phosphate oxidase.

Loubbardi A A Marcireau C C Karst F F Guilloton M M

Journal of bacteriology 19950401 7

Exogenous sterols do not permeate wild-type Saccharomyces cerevisiae in aerobic conditions. However, mutant strain FKerg7, affected in lanosterol synthase, is a sterol auxotroph which is able to grow aerobically in the presence of ergosterol. Viability of this strain depends on the presence of an additional mutation, aux30, that leads to sterol permeability. Cells bearing the aux30 mutation fail to grow in standard yeast nitrogen base medium containing pyridoxine but grow normally if pyridoxine ...[more]

PMID: 7896706

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Project description:Escherichia coli YggS (COG0325) is a member of the highly conserved pyridoxal 5'-phosphate (PLP)-binding protein (PLPBP) family. Recent studies suggested a role for this protein family in the homeostasis of vitamin B6 and amino acids. The deletion or mutation of a member of this protein family causes pleiotropic effects in many organisms and is causative of vitamin B6-dependent epilepsy in humans. To date, little has been known about the mechanism by which lack of YggS results in these diverse phenotypes. In this study, we determined that the pyridoxine (PN) sensitivity observed in yggS-deficient E. coli was caused by the pyridoxine 5'-phosphate (PNP)-dependent overproduction of Val, which is toxic to E. coli The data suggest that the yggS mutation impacts Val accumulation by perturbing the biosynthetic of Thr from homoserine (Hse). Exogenous Hse inhibited the growth of the yggS mutant, caused further accumulation of PNP, and increased the levels of some intermediates in the Thr-Ile-Val metabolic pathways. Blocking the Thr biosynthetic pathway or decreasing the intracellular PNP levels abolished the perturbations of amino acid metabolism caused by the exogenous PN and Hse. Our data showed that a high concentration of intracellular PNP is the root cause of at least some of the pleiotropic phenotypes described for a yggS mutant of E. coliIMPORTANCE Recent studies showed that deletion or mutation of members of the YggS protein family causes pleiotropic effects in many organisms. Little is known about the causes, mechanisms, and consequences of these diverse phenotypes. It was previously shown that yggS mutations in E. coli result in the accumulation of PNP and some metabolites in the Ile/Val biosynthetic pathway. This work revealed that some exogenous stresses increase the aberrant accumulation of PNP in the yggS mutant. In addition, the current report provides evidence indicating that some, but not all, of the phenotypes of the yggS mutant in E. coli are due to the elevated PNP level. These results will contribute to continuing efforts to determine the molecular functions of the members of the YggS protein family.

Dataset Information

Sterol uptake induced by an impairment of pyridoxal phosphate synthesis in Saccharomyces cerevisiae: cloning and sequencing of the PDX3 gene encoding pyridoxine (pyridoxamine) phosphate oxidase.

Publications

Sterol uptake induced by an impairment of pyridoxal phosphate synthesis in Saccharomyces cerevisiae: cloning and sequencing of the PDX3 gene encoding pyridoxine (pyridoxamine) phosphate oxidase.

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