Cloning and characterization of the Hansenula polymorpha homologue of the Saccharomyces cerevisiae PMR1 gene

Identification and characterization of calcium and manganese transporting ATPase (PMR1) gene of Pichia pastoris

A gene homologous to Saccharomyces cerevisiae PMR1 has been cloned in the methylotrophic yeast Pichia pastoris. The entire P. pastoris PMR1 gene (PpPMR1) codes a protein of 924 amino acids. Sequence analysis of the PpPMR1 cDNA and the genomic DNA revealed that there is no intron in the coding region. The putative gene product contains all of the conserved regions observed in P-type ATPases and exhibits 66.2%, 60.3% and 50.6% identity to Pichia angusta (Hansenula polymorpha), Saccharomyces cerevisiae PMR1 and human ATP2C1 gene products, respectively. A pmr1 null mutant strain of P. pastoris exhibited growth defects in media with the addition of EGTA, but with supplementation of Ca2+ to a calcium-deficient media reversed the growth defects of the mutant strain. Manganese reversed the growth defects of the mutant strain; however, the cell growth was not as profound as the Ca2+ -supplemented media. The results demonstrated that the P. pastoris gene encodes the functional homologue of the S. cerevisiae PMR1 gene product, a P-type Ca2+/Mn2+ -ATPase. The DNA sequence of the P. pastoris PMR1 gene has been submitted to GenBank under Accession No. DQ239958.

A PMR1-like calcium ATPase ofAspergillus fumigatus: cloning, identification and functional expression inS. cerevisiae

The understanding of the controlling factors of calcium homeostasis in Aspergillus fumigatus is very poor, although this ion is involved in several important events of these particular cells. We have cloned, identified and expressed for functional complementation a PMR1-like Ca(2+)-ATPase gene from A. fumigatus. The Afpmr1 gene encodes a protein of 1061 deduced amino acids, containing all the conserved subdomains found in other P-type ATPases: the phosphatase region, phosphorylation site, FITC labelling site, ATP binding domain; E(386), N871, D875 amino acid residues for calcium ion interaction and Q880, a residue that alters ion selectivity in PMR1. The expressed AfPMR1 in S. cerevisiae K616 strain functionally complemented the deficient growth in EGTA (5-20 mM)- and MnCl2 (4 mM)-containing medium. These results demonstrate the first evidence of a Ca(2+)-ATPase in A. fumigatus and strongly suggest a role for this enzyme in calcium and manganese homeostasis.

C-terminal truncation of alpha-COP affects functioning of secretory organelles and calcium homeostasis in Hansenula polymorpha

In eukaryotic cells, COPI vesicles retrieve resident proteins to the endoplasmic reticulum and mediate intra-Golgi transport. Here, we studied the Hansenula polymorpha homologue of the Saccharomyces cerevisiae RET1 gene, encoding alpha-COP, a subunit of the COPI protein complex. H. polymorpha ret1 mutants, which expressed truncated alpha-COP lacking more than 300 C-terminal amino acids, manifested an enhanced ability to secrete human urokinase-type plasminogen activator (uPA) and an inability to grow with a shortage of Ca2+ ions, whereas a lack of alpha-COP expression was lethal. The alpha-COP defect also caused alteration of intracellular transport of the glycosylphosphatidylinositol-anchored protein Gas1p, secretion of abnormal uPA forms, and reductions in the levels of Pmr1p, a Golgi Ca2+-ATPase. Overexpression of Pmr1p suppressed some ret1 mutant phenotypes, namely, Ca2+ dependence and enhanced uPA secretion. The role of COPI-dependent vesicular transport in cellular Ca2+ homeostasis is discussed.

Functional expression of heterologous proteins in yeast: insights into Ca2+signaling and Ca2+-transporting ATPases

The baker's yeast Saccharomyces cerevisiae is a well-developed, versatile, and widely used model organism. It offers a compact and fully sequenced genome, tractable genetics, simple and inexpensive culturing conditions, and, importantly, a conservation of basic cellular machinery and signal transducing pathways with higher eukaryotes. In this review, we describe recent technical advances in the heterologous expression of proteins in yeast and illustrate their application to the study of the Ca2+homeostasis machinery, with particular emphasis on Ca2+-transporting ATPases. Putative Ca2+-ATPases in the newly sequenced genomes of organisms such as parasites, plants, and vertebrates have been investigated by functional complementation of an engineered yeast strain lacking endogenous Ca2+pumps. High-throughput screens of mutant phenotypes to identify side chains critical for ion transport and selectivity have facilitated structure-function analysis, and genomewide approaches may be used to dissect cellular pathways involved in Ca2+transport and trafficking. The utility of the yeast system is demonstrated by rapid advances in the study of the emerging family of Golgi/secretory pathway Ca2+,Mn2+-ATPases (SPCA). Functional expression of human SPCA1 in yeast has provided insight into the physiology, novel biochemical characteristics, and subcellular localization of this pump. Haploinsufficiency of SPCA1 leads to Hailey-Hailey disease (HDD), a debilitating blistering disorder of the skin. Missense mutations, identified in patients with HHD, may be conveniently assessed in yeast for loss-of-function phenotypes associated with the disease.

Secretory expression and purification of Aspergillus niger glucose oxidase in Saccharomyces cerevisiae mutant deficient in PMR1 gene

The gene encoding glucose oxidase (GOD) from Aspergillus niger was expressed as a secretory product in the yeast Saccharomyces cerevisiae. Six consecutive histidine residues were fused to the C-terminus of GOD to facilitate purification. The recombinant GOD-His(6) secreted by S. cerevisiae migrated as a broad diffuse band on SDS-PAGE, with an apparent molecular weight higher than that in natural A. niger GOD. To investigate the effects of hyperglycosylation on the secretion efficiency and enzyme properties, GOD-His(6) was expressed and secreted in a S. cerevisiae mutant in which the PMR1 gene encoding Ca(++)-ATPase was disrupted. The pmr1 null mutant strain secreted an amount of GOD-His(6) per unit cell mass higher than that in the wild-type strain. In contrast to the hyperglycosylated GOD-His(6) secreted in the wild-type strain, the pmr1 mutant strain secreted GOD-His(6) in a homogeneous form with a protein band pattern similar to that in natural A. niger GOD, based on SDS-PAGE. The hyperglycosylated and pmr1Delta mutant-derived GOD-His(6) enzymes were purified to homogeneity by immobilized metal ion-affinity chromatography and their specific activities and stabilities were compared. The specific activity of the pmr1Delta mutant-derived GOD-His(6) on a protein basis was very similar to that of the hyperglycosylated GOD-His(6), although its pH and thermal stabilities were lower than those of the hyperglycosylated GOD-His(6).

Cloning of the Aspergillus niger pmrA gene, a homologue of yeast PMR1, and characterization of a pmrA null mutant

The pmrA gene, a yeast PMR1 homologue, was isolated from Aspergillus niger. Sequence analysis of the pmrA cDNA and the genomic DNA revealed that two introns exist in the coding region, and that an open reading frame in the cDNA encodes a polypeptide of 1056 amino acids containing all the conserved regions present in P-type Ca2+-ATPases. The predicted pmrA protein exhibited a high degree of sequence similarity to the Pmr1 proteins from yeasts and mammalians (50-59% identity). The expression of the pmrA cDNA partially restored the growth defect of Yarrowia lipolytica pmr1 null mutant on EGTA-containing medium. This indicates that the A. niger pmrA gene encodes a functional homologue of the yeast P-type Ca2+-ATPase involved in the secretory pathway. An A. niger pmrA null mutant exhibited growth retardation on EGTA-containing medium and the growth defect was overcome by adding Ca2+ or Mn2+ into the medium. This suggests an involvement of the pmrA protein in Ca2+ and Mn2+ homeostasis in A. niger.

Molecular cloning of the calcium and sodium ATPases in Neurospora crassa

Using PCR, reverse transcription-PCR (RT-PCR) and colony hybridization in a genomic library, we isolated six genes which encode type II P-type ATPases in Neurospora crassa. The six full-length cDNAs were cloned in a yeast expression vector and transformed into Saccharomyces cerevisiae null Ca2+- or Na+-ATPase mutants. Three cDNAs suppressed the defect of the Ca2+ mutant and two of these protected from Mn2+ toxicity. One cDNA suppressed the defect of the Na+ mutant and two cDNAs were not functional in S. cerevisiae. The expression of the transcripts of the six genes in the presence of Ca2+, Na+, high pH or supporting an osmotic shock indicated that, with the exception of one of the Ca2+-ATPases, the main function of the cloned ATPases is the adaptation to stress conditions. The relationship between the cloned fungal Ca2+- and Na+-ATPases and plant type II P-ATPases is discussed.

The KlPMR1 gene of Kluyveromyces lactis encodes for a P-type Ca(2+)-ATPase

A novel P-type Ca(2+)-ATPase gene has been cloned and sequenced in the yeast Kluyveromyces lactis. The gene has been named KlPMR1 and is localized on chromosome I. The putative gene product contains 936 residues and has a calculated molecular weight of 102,437 Da. Analysis of deduced amino acid sequence (KlPmr1p) indicated that the encoded protein retains all the highly conserved domains characterizing the P-type ATPases. KlPmr1p shares 71% amino acid identity with Pmr1p of S. cerevisiae, 62% with HpPmr1p of Hansenula polymorpha, 56% with Y1Pmr1p of Yarrowia lipolytica and 52% with the Ca(2+)-ATPase encoded for by the SPCA1 gene of Rattus norvegicus; these similarities place KlPmr1p in the SPCA group (secretory pathway Ca(2+)-ATPase) of the P-type ATPases. The K. lactis strain harbouring the Klpmr1 disrupted gene is not able to grow in presence of low calcium concentrations and shows hypersensitivity to high concentrations of EGTA in the medium. These defects are relieved by PMR1 of S. cerevisiae on a centromeric plasmid, demonstrating that KlPMR1 encodes for a functional Pmr1p homologue.