Abstract
The closely related yeasts Ogataea polymorpha and O. parapolymorpha differ drastically from each other by sensitivity to the toxic phosphate analog vanadate. Search for genes underlying this difference revealed two genes, one designated as ABV1 (Alcian Blue staining, Vanadate resistance), which encodes a homologue of Saccharomyces cerevisiae Mnn4 responsible for attachment of mannosylphosphate to glycoside chains of secretory proteins, and the other designated as its S. cerevisiae homologue PHO87, encoding the plasma membrane low affinity phosphate sensor/transporter. The effect of Pho87 on vanadate resistance was bidirectional, since it decreased the resistance on phosphate-depleted medium, but was required for pronounced protection against vanadate by external phosphate. This highlights the dual function of this protein as a low affinity phosphate transporter and an external phosphate sensor. Involvement of Pho87 in phosphate sensing was confirmed by its effects on regulation of the promoter of the PHO84 gene, encoding a high affinity phosphate transporter. The effect of Abv1 was also complex, since it influenced Pho87 level and enhanced repression of the PHO84 promoter via a Pho87-independent pathway. Role of the identified genes in the difference in vanadate resistance between O. polymorpha and O. parapolymorpha is discussed.
Highlights
Inorganic phosphate (Pi) is a crucial nutrient for living cells
At low external Pi concentration, the presence of the plasma membrane low affinity Pi transporters can be detrimental to the cell, and this effect can be alleviated by targeting these proteins for vacuolar degradation via the endocytic pathway[7]
The core of this circuit involves a complex consisting of cyclin-dependent protein kinase (CDK) Pho[85], one of its cyclins Pho[80], and the CDK
Summary
Inorganic phosphate (Pi) is a crucial nutrient for living cells. As the plasma membrane is impermeable to this cation, its uptake depends on special transporters. With Pho[2] and causes its redistribution from the nucleus to the cytosol[12,13,14,15] Apart from this circuit, regulation of PHO84, which depends on the low affinity Pi transporters and does not depend on internal Pi concentration, has been elucidated[16]. Vanadate (orthovanadate, VO43−) is a toxic Pi analog, which has multiple targets within the cell It efficiently inhibits many different enzymes, whose substrates carry a phosphate moiety[18]. Compared to S. cerevisiae, Ogataea (Hansenula) polymorpha is much more resistant to this compound[23], while its closest relative O. parapolymorpha[24] is not[25] We used these two yeast species to gain insight into the mechanisms involved in vanadate resistance and its relation to Pi transport and protein glycosylation
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