Biomedical subjects

M E Evers

Publications and source records attributed to M E Evers.

10 recordsLinked to original sources

PubMed1996

Identification and characterization of cytosolic Hansenula polymorpha proteins belonging to the Hsp70 protein family.

We have isolated two members of the Hsp70 protein family from the yeast Hansenula polymorpha using affinity chromatography. Both proteins were located in the cytoplasm. One of these, designated Hsp72, was inducible in nature (e.g. by heat shock). The second protein (designated Hsc74) was constitutively present. Peptides derived from both Hsp72 and Hsc74 showed sequence homology to the cytosolic Saccharomyces cerevisiae Hsp70s, Ssa1p and Ssa2p. The gene encoding Hsp72 (designated HSA1) was cloned, sequenced and used to construct HSA1 disruption and HSA1 overexpression strains. Comparison of the stress tolerances of these strains with those of wild-type H. polymorpha revealed that HSA1 overexpression negatively affected the tolerance of the cells to killing effects of temperature or ethanol, but enhanced the tolerance to copper and cadmium. The tolerance for other chemicals (arsenite, arsenate, H2O2) or to high osmolarity was unaffected by either deletion or overexpression of HSA1.

Cadmium↗

PubMed1996

Flavin adenine dinucleotide binding is the crucial step in alcohol oxidase assembly in the yeast Hansenula polymorpha.

We have studied the role of flavin adenine dinucleotide (FAD) in the in vivo assembly of peroxisomal alcohol oxidase (AO) in the yeast Hansenula polymorpha. In previous studies, using a riboflavin (Rf) autotrophic mutant, an unequivocal judgement could not be made, since Rf-limitation led to a partial block of AO import in this mutant. This resulted in the accumulation of AO precursors in the cytosol where they remained separated from the putative peroxisomal AO assembly factors. In order to circumvent the peroxisomal membrane barrier, we have now studied AO assembly in a peroxisome-deficient/Rf-autotrophic double mutant (delta per1.rif1) of H. polymorpha. By sucrose density centrifugation and native gel electrophoresis, three conformations of AO were detected in crude extracts of delta per1.rif1 cells grown under Rf-limitation, namely active octameric AO and two inactive, monomeric forms. One of the latter forms lacked FAD; this form was barely detectable in extracts wild-type and delta per1 cells, but had accumulated in the cytosol of rif1 cells. The second form of monomeric AO contained FAD; this form was also present in delta per1 cells but absent/very low in wild-type and rif1 cells. In vivo only these FAD-containing monomers associate into the active, octameric protein. We conclude that in H. polymorpha FAD binding to the AO monomer is mediated by a yet unknown peroxisomal factor and represents the crucial and essential step to enable AO oligomerization; the actual octamerization and the eventual crystallization in peroxisomes most probably occurs spontaneously.

Alcohol Oxidoreductases↗

PubMed1995

Restoration of peroxisome formation in two conditional peroxisome-deficient mutants of Hansenula polymorpha during growth of cells on specific organic nitrogen sources.

Expression of the peroxisome-deficient (Per-) phenotype by per mutants Hansenula of polymorpha is shown to be dependent on specific environmental conditions. Analysis of our collection of constitutive and conditional per mutants showed that, irrespective of the carbon source used, the mutants invariably lacked functional peroxisomes when ammonium sulphate was used as a nitrogen source. However, in two temperature-sensitive (ts) mutants, per13-6ts and per14-11ts, peroxisomes were present at the restrictive temperature when cells were grown on organic nitrogen sources which are known to induce peroxisomes in wild-type cells, namely D-alanine (for both mutants) or methylamine (for per14-11ts). These organelles displayed normal wild-type properties with respect to morphology, mode of development and protein composition. However, under these conditions not all the peroxisomal matrix proteins synthesized were correctly located inside peroxisomes. Detailed biochemical and (immuno)cytochemical analyses indicated that during growth of cells on methanol in the presence of either D-alanine or methylamine, a minor portion of these proteins (predominantly alcohol oxidase, dihydroxyacetone synthase and catalase) still resided in the cytosol. This residual cytosolic activity may explain the observation that the functional restoration of the two ts mutants is not complete under these conditions, as is reflected by the retarded growth of the cells in batch cultures on methanol.

Cell Fractionation↗

PubMed1995

In vitro dissociation and re-assembly of peroxisomal alcohol oxidases of Hansenula polymorpha and Pichia pastoris.

We have studied the in vitro inactivation/dissociation and subsequent reactivation/re-assembly of peroxisomal alcohol oxidases (AO) from the yeasts Hansenula polymorpha and Pichia pastoris. Both proteins are homo-oligomers consisting of eight identical subunits, each containing one FAD as the prosthetic group. They were both rapidly inactivated upon incubation in 80% glycerol, due to their dissociation into the constituting subunits, which however still contained FAD. Dilution of dissociated AO in neutral buffer lead to reactivation of the protein due to AO re-assembly, as was demonstrated by non-denaturing PAGE. After use of mixtures of purified AO from H. polymorpha and P. pastoris active hybrid AO oligomers were formed. When prior to dissociation FAD was chemically removed from AO, reactivation or re-assembly did not occur independent of externally added FAD.

Alcohol Oxidoreductases↗

PubMed1995

Aplasia cutis congenita and associated disorders: an update.

We present an update of disorders in which aplasia cutis congenita is a feature. Localization of the lesion, important other features, and possible etiology are tabulated. Disorders are classified as chromosomal, monogenic, teratological/exogenous, and unknown. Points of particular interest in history taking and examination of patients with aplasia cutis congenita are presented.

Ectodermal Dysplasia↗

PubMed1994

Oculo-ectodermal syndrome: a new case.

We report on a girl with aplasia cutis congenita, epibulbar dermoids, and macrocephaly. To our opinion she has the same ocular-ectodermal syndrome as described by Toriello et al. [Am J Med Genet 45: 764-766, 1993].

Dermoid Cyst↗

PubMed1994

Assembly of alcohol oxidase in peroxisomes of the yeast Hansenula polymorpha requires the cofactor flavin adenine dinucleotide.

The peroxisomal flavoprotein alcohol oxidase (AO) is an octamer (600 kDa) consisting of eight identical subunits, each of which contains one flavin adenine dinucleotide molecule as a cofactor. Studies on a riboflavin (Rf) auxotrophic mutant of the yeast Hansenula polymorpha revealed that limitation of the cofactor led to drastic effects on AO import and assembly as well as peroxisome proliferation. Compared to wild-type control cells Rf-limitation led to 1) reduced levels of AO protein, 2) reduced levels of correctly assembled and activated AO inside peroxisomes, 3) a partial inhibition of peroxisomal protein import, leading to the accumulation of precursors of matrix proteins in the cytosol, and 4) a significant increase in peroxisome number. We argue that the inhibition of import may result from the saturation of a peroxisomal molecular chaperone under conditions that normal assembly of a major matrix protein inside the target organelle is prevented.

Alcohol Oxidoreductases↗

PubMed1993

Affinity purification of molecular chaperones of the yeast Hansenula polymorpha using immobilized denatured alcohol oxidase.

We used peroxisomal alcohol oxidase (AO) for the affinity purification of molecular chaperones from yeasts. Methodical studies showed that up to 0.8 mg of purified bacterial GroEL was able to bind per ml of immobilized denatured AO column material. Using crude extracts of Hansenula polymorpha or Saccharomyces cerevisiae, several proteins were specifically eluted with Mg-ATP which were recognized by antibodies against hsp60 or hsp70. One H. polymorpha 70 kDa protein was strongly induced during growth at elevated temperatures, whereas a second 70 kDa protein as well as a 60 kDa protein showed strong protein sequence homology to mitochondrial SSC1 and hsp60, respectively, from S. cerevisiae.

Alcohol Oxidoreductases↗

PubMed1992

Formation and quantification of protein complexes between peroxisomal alcohol oxidase and GroEL.

We have studied the use of yeast peroxisomal alcohol oxidase (AO) as a model protein for in vitro binding by GroEL. Dilution of denatured AO in neutral buffer leads to aggregation of the protein, which is prevented by the addition of GroEL. Formation of complexes between GroEL and denatured AO was demonstrated by a gel-shift assay using non-denaturing polyacrylamide gel electrophoresis, and quantified by laser-densitometry of the gels. In the presence of MgAMP-PNP or MgADP the affinity of GroEL for AO was enhanced. Under these conditions up to 70% of the purified GroEL formed a complex with this protein. Release was stimulated at room temperature by MgATP, and was further enhanced by addition of GroES.

Alcohol Oxidoreductases↗

PubMed1991

Physiological studies on the utilization of oleic acid by Saccharomyces cerevisiae in relation to microbody development.

We studied the influence of specific growth conditions on the induction of beta-oxidation enzymes and rate of microbody proliferation in S. cerevisiae by oleic acid. Of all conditions tested, highest enzyme levels and microbody numbers were achieved in glucose-limited continuous cultures, supplemented with oleic acids second carbon source. Comparable enzyme levels were observed in identical cultures of peroxisome-deficient (pas) mutants of S. cerevisiae. These experiments showed chemostat cultures on glucose/oleic acid mixtures to be a method of choice for future studies on microbody biogenesis/assembly in constructed, conditional pas mutants.

Cell Division↗